Materials doi: 10.3390/ma19163383

Authors: Peiwen Xiao Kai Lv Xiang Peng Jie Li Qun Zhang Yuanping Lin Yanqi Li Weidong Liu Yinzhu Ye

This study addresses the limitations of traditional chemical flooding in low-permeability reservoirs by developing a nanofluid–surfactant binary flooding system (Has5/iNanoW1.0 binary flooding system) and investigating its microscopic mechanisms and enhanced oil recovery performance. The size of the nanofluid–surfactant binary flooding system reduces from 250 nm to 72 nm compared with pure surfactant; therefore it can enhance the ability to inject smaller pores. Core adsorption tests reveal that the addition of nanofluid can decrease surfactant adsorption by over 30%. The nanoscale synergistic effect of nanofluid (iNanoW1.0) and surfactant (Has5) and lower adsorption of surfactant allows more surfactant (Has5) to enter smaller pores for oil washing, significantly increasing oil recovery performance. Low-field nuclear magnetic resonance displacement experiments show that the binary system can significantly expand microscopic sweep efficiency (up to 14.9%) compared to pure surfactant or nanofluid flooding. Core flooding tests confirm that the binary system exhibits lower injection pressure (0.377 MPa), achieving 13.12% incremental oil recovery during post-water flooding, which is significantly better than the pure surfactant system (5.11%). The results demonstrate strong laboratory-scale potential and permit further pilot-scale evaluation.

Materials doi: 10.3390/ma19163382

Authors: Lili Ran Shilin Liu Ba Li Yanan Li Rui Hong Bing Wang Qingyou Liu Shujun Jia

Gleeble-3800 thermal simulation testing machine was adopted to investigate the evolution laws of microstructure and properties in the coarse-grained heat-affected zone (CGHAZ) of pipeline steels with different Cr mass fractions (0.2, 0.5, 0.8 wt.%) under welding heat inputs ranging from 8 kJ/cm to 20 kJ/cm. Combined with optical microscopy, scanning electron microscopy and electron backscatter diffraction, the coupled influencing mechanism of heat input and Cr content on the properties of CGHAZ was systematically analyzed. The results show that as the Cr content increases, the range of valid welding heat input for maintaining satisfactory CGHAZ impact toughness gradually narrows with increasing Cr mass fraction of the steel. Specifically, the 0.2Cr experimental steel maintains high toughness under a thermal input ranging from 8 to 20 kJ/cm, the 0.5Cr experimental steel exhibits relatively high toughness in the range 8 to 13 kJ/cm, while the 0.8Cr experimental steel shows high toughness only at 15 kJ/cm. The coupled effect of weld heat input and Cr content on CGHAZ properties originates from a combination of microstructural composition types, phase fractions, substructures, and grain sizes. Increasing the heat input and Cr content leads to a reduction in the bainite ferrite with superior toughness and an increase in the large-sized granular bainite with inferior toughness. Meanwhile, the effective grain size of the overall microstructure first decreases and then rises. Grain coarsening and an increased fraction of Martensitic/Austenitic (M/A) constituent are the key factors responsible for the deterioration of CGHAZ toughness in deep-sea oil and gas transportation pipeline steel.

Materials doi: 10.3390/ma19163381

Authors: Ayşe Rençber Kızılkaya Kübra Bilge Aybüke Kara

This in vitro study compared the fracture load of multilayer zirconia onlay restorations with different yttria contents after thermomechanical aging. Standardized CAD/CAM-fabricated onlay restorations were produced from three multilayer zirconia materials: one color-gradient material (KATANA Zirconia UTML; 5Y-TZP) and two strength-gradient materials (KATANA Zirconia YML, 3–5Y-TZP; IPS e.max ZirCAD MT Multi, 4–5Y-TZP) (n = 10/group). The restorations were cemented onto three-dimensionally printed resin dies and subjected to 240,000 loading cycles and 5000 thermal cycles. Fracture load was measured using a universal testing machine, and the data were analyzed by one-way analysis of variance, Tukey’s post hoc test, and Weibull analysis (α = 0.05). Fracture load differed significantly among the materials (p = 0.017). The UTML group (395.73 N) exhibited a significantly lower fracture load than the YML group (618.19 N), whereas the ZirCAD MT Multi group (565.24 N) did not differ significantly from either of the other two groups. Weibull analysis revealed no significant differences in modulus among the groups, whereas the characteristic load of the UTML group was significantly lower than that of the other two materials (p = 0.002). Within the conditions of this in vitro study, the strength-gradient materials, which contain lower yttria concentrations in their underlying layers, showed higher fracture loads after thermomechanical aging than the color-gradient material. These findings are limited to the tested laboratory conditions and require clinical confirmation.

Materials doi: 10.3390/ma19163380

Authors: Lei Zhao Guanghui Yang

This study proposes a targeted sound-absorption design strategy to address the challenge of broadband and low-frequency transformer noise. Based on field measurements, transformer noise is identified as being characterized by a dominant 100 Hz fundamental component, pronounced low-order harmonics in the range of 200–500 Hz, and an overall broadband distribution within 100–1000 Hz. To meet these noise-control requirements, a composite acoustic metamaterial based on a traditional Helmholtz resonator and a side-slit Helmholtz resonator (HRSS-HR) is proposed. An electro-acoustic analogy model is established to predict its acoustic performance and is validated through finite element simulation and impedance tube experiments, thereby revealing the underlying sound-absorption mechanisms. The proposed composite unit cell exhibits four characteristic absorption peaks over a broad frequency range, among which the peaks within 100–1000 Hz are directly relevant to transformer noise control. We systematically investigate the evolution of sound absorption from a single unit to coupled parallel structures and then to a 4 × 4 array, leveraging the tunability of the HRSS-HR structure. Parallel coupling broadens the effective absorption bandwidth but weakens the original impedance matching condition, whereas increasing the slit width and decreasing the neck height can effectively recover the low- and middle-frequency absorption performance. Finally, a 4 × 4 HRSS-HR composite metamaterial array is developed. Both simulation and experiment confirm that the optimized array maintains relatively high absorption levels near 100 Hz and the major harmonic bands of 200–500 Hz, while preserving good broadband absorption capability over 100–1000 Hz. This work validates the strong application potential of the proposed HRSS-HR design in transformer broadband noise control and offers a practical solution for low-frequency harmonic noise mitigation in transformers and similar power equipment.

Materials doi: 10.3390/ma19163379

Authors: Filipa G. Cunha Telmo G. Santos José Xavier

Functionally Graded Materials (FGMs) vary in composition and properties for tailored structural performance. Additive Manufacturing (AM), particularly Wire Arc Additive Manufacturing (WAAM), offers a scalable route to metallic FGMs, but manufacture and mechanical qualification remain disconnected. Scopus and Web of Science Core Collection were searched for eligible publications up to and including 31 July 2026. The review includes 176 studies, and every conclusion is graded by a review-specific certainty scheme and bounded to this corpus. The review connects FGM manufacture with full-field inverse identification of spatially varying properties. Evidence indicates interface-defect risk depends on metallurgical compatibility and the composition path. Intermetallic-forming or thermally mismatched pairs remain vulnerable despite process optimisation. Stainless-steel–Ni-superalloy combinations are more frequently reported as sound but only within the composition intervals validated in the cited builds: this apparent advantage reflects unequal study numbers and cracking in specific composition windows. A four-stage sequence—screening phase stability and thermal-expansion mismatch before optimising deposition parameters, then validating the complete composition path—is proposed as an evidence-informed framework rather than a validated decision map. Conventional tests generally provide averaged or location-specific properties rather than a continuous constitutive gradient. Digital image correlation coupled with inverse identification methods can enable the determination of spatially varying properties from a heterogeneous test. However, no experimental study identified a spatial constitutive law across a deliberate WAAM compositional gradient.

Materials doi: 10.3390/ma19163377

Authors: Marta Kaczmarek Marcin Przybylak Agnieszka Dutkiewicz Hieronim Maciejewski

In this study, two epoxy-functional polysiloxanes were synthesized and applied for cotton hydrophobization using two modification routes: direct reactive deposition and thiol-crosslinking on the fiber surface. PS1 contained epoxy groups, whereas PS2 contained both epoxy groups and alkyl chains. The modified fabrics were characterized by add-on measurements, FT-IR spectroscopy, SEM-EDS, SEM imaging, washing tests, and static water contact angle measurements. Both modification strategies enabled the formation of polysiloxane-based layers on cotton, as confirmed by the presence of silicon in all modified samples and sulfur in thiol-crosslinked samples. SEM images showed continuous and relatively uniform coatings without visible fiber damage. All modified fabrics became hydrophobic and retained their properties after washing. Thiol-crosslinking was more effective than direct reactive deposition, giving WCA values up to 144°. PS1 provided stable hydrophobicity regardless of thiol type or concentration, while PS2 benefited from higher modifier concentration and the use of tetrafunctional thiol. The results show that epoxy-functional polysiloxanes, especially when crosslinked with multifunctional thiols, are effective modifiers for producing washable hydrophobic cotton fabrics.

Materials doi: 10.3390/ma19163378

Authors: João R. Da Fonseca Borja Caja-Muñoz María E. Dávila Juan P. Martínez-Pastor Juan F. Sánchez-Royo Maria C. Asensio

We compare the ionic transport properties of six LiFeO2 polymorphs side by side to assess their potential as intercalation cathodes for lithium-ion batteries (LIBs). Employing two established methods, Bond Valence Site Energy (BVSE) calculations and Crystal Analysis by Voronoi Decomposition (CAVD), with identical settings for all six structures, we analyze how structural variations affect Li-ion diffusion pathways, dimensionalities, and migration barriers. Within this comparison, the ordered rock salt phase shows the most favorable transport characteristics, combining the lowest energy barriers of the six polymorphs with three-dimensional Li-ion conduction. The tetrahedral polymorph also has a three-dimensional void network, but its lowest-energy migration is one-dimensional, and the network connects in all three dimensions only at considerably higher energy. In contrast, layered and corrugated structures enable quasi-two-dimensional diffusion but are limited by high out-of-plane barriers. The goethite and γ phases are the most constrained. Goethite confines low-energy migration to a single axis, and in γ-LiFeO2, high barriers in every direction leave the geometrically connected network kinetically ineffective. Together, the results provide a consistent structure–transport comparison across the six polymorphs that can guide the choice of LiFeO2 phases for further cathode development.

Materials doi: 10.3390/ma19163376

Authors: Yuting Song Yujie Ao Qiao Deng Linwei Zhang Jilin Liu Zichun Wu Jiancheng Tang Nan Ye

Solid solution with molybdenum is an effective strategy for improving the overall performance of tungsten alloys, thereby enhancing their application potential in aerospace and other fields. In this study, highly dense W-Mo alloy specimens were successfully fabricated using laser powder bed fusion, followed by stress-relief annealing. The results show that the complete solid solution of molybdenum yields a fine columnar grain structure with weak texture. After stress-relief annealing, the residual stress decreases, the grain size increases slightly, and the fraction of the <111>//building direction (BD) texture rises. Ultimately, W-Mo alloy specimens with excellent compressive properties are obtained, with compressive yield strength, ultimate compressive strength, and compressive strain reaching 879.5 MPa, 1257.3 MPa, and 16.6%, respectively. This work provides new insights into the fabrication of refractory alloys by laser powder bed fusion.

Materials doi: 10.3390/ma19163375

Authors: Farhan Akhtar Wajid Ali Muhammad Saqib Syed Adil Sardar Tabinda Shabir Muhammad Awais Samina Karim Woo Young Kim

Hydrogen produced through electrochemical water splitting is considered one of the most promising energy carriers for achieving a sustainable and carbon-neutral future. However, the practical implementation of water electrolysis remains limited by the sluggish kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), as well as the high cost and limited availability of conventional noble-metal catalysts. Single-atom catalysts (SACs), which feature isolated metal atoms anchored on suitable supports, have emerged as an attractive class of electrocatalysts owing to their nearly complete atomic utilization, well-defined active sites, and tunable electronic structures. This review provides a comprehensive overview of recent advances in SACs for electrochemical water splitting. The fundamental mechanisms of HER and OER are first discussed, followed by the influence of the unique electronic structure, coordination environment, and metal–support interactions on catalytic performance. Various bottom-up and top-down synthesis strategies, together with advanced characterization techniques for identifying atomically dispersed active sites and elucidating structure–activity relationships, are systematically summarized. Furthermore, recent progress in noble-metal, non-noble-metal, and dual-atom catalysts is critically reviewed, with emphasis on their roles in regulating electronic structure, reaction intermediate adsorption, catalytic activity, HER/OER kinetics, and long-term stability. Finally, the remaining challenges and future perspectives for the scalable and practical application of SACs in water electrolysis are discussed. Overall, this review highlights the potential of SACs to maximize metal utilization while maintaining high electrocatalytic performance and provides valuable insights for the rational design of next-generation electrocatalysts for sustainable hydrogen production.

Materials doi: 10.3390/ma19163374

Authors: Chenghua Gao Ao Meng Zihao Wang Wei Jiang Zhumin Li Yu Zhao Jiansheng Li

To elucidate the effect of cyclic hot forging and short-time aging (HFSTA) on the wear resistance of a Cu-Cr-Zr alloy, samples in the as-received state (solution-treated at 1000 °C) and after 4 passes and 6 passes of cyclic HFSTA at 450 °C were prepared. The relationships between microstructure and properties were systematically analyzed. The results indicate that the cyclic HFSTA process did not change the main phase structure of the Cu matrix but significantly tailored the grain morphology, local misorientation, grain boundary character, and tribo-chemical behavior of the surface. The 4-passes sample possessed relatively high hardness, electrical conductivity, and favorable microstructural stability and was able to form a continuous and dense oxide protective film during friction, as demonstrated by the increase in hardness from 86 HV (as-received) to 195 HV, the decrease in average coefficient of friction (COF) from 0.65 to 0.50, and the reduction in wear rate from 13.3 × 10−4 mm3/(N·m) to 0.3 × 10−4 mm3/(N·m). The 6-passes sample exhibited slightly higher hardness, but the increased proportion of low-angle grain boundaries (LAGBs) intensified cracking and spallation on the wear track, causing the wear rate to rebound to approximately 8.2 × 10−4 mm3/(N·m). The study demonstrates that the wear resistance of the Cu-Cr-Zr alloy does not improve monotonically with hardness or grain refinement but is jointly controlled by precipitation strengthening, dislocation/substructure strengthening, surface damage tolerance, and the stability of the tribo-film. For the dry sliding service conditions of Cu-Cr-Zr alloys, 4 passes of cyclic HFSTA at 450 °C represent an optimal processing window that balances mechanical properties, electrical conductivity, and wear resistance, providing guidance for the process optimization of components such as contact wires and welding electrodes.

Materials doi: 10.3390/ma19163373

Authors: Deyu Zheng Guoqing Zhang Xiaoyan Sun Jingjing Liu Yejun Xu Haitao Wang

During hot deformation of GH4706 alloy forgings, to achieve effective control over the uniformity of its microstructure, it is first necessary to establish a quantitative relationship between the microstructural characteristics of an entire hot-formed turbine disk forging and process parameters using reliable methods. Based on hot compression test results of GH4706 alloy at temperatures ranging from 950 °C to 1150 °C and strain rates from 0.001 s−1 to 1 s−1, this study developed a microstructure evolution model. Multi-scale high-precision numerical simulations were performed to predict the parameter field distribution and microstructure distribution of the turbine disk. The results reveal that the inhomogeneity of strain distribution is the primary cause of mixed grain formation. Statistical comparisons between simulation predictions at six validation points and industrial experimental data revealed the following relative deviations: 5.21% for average grain size (AVG), 9.65% for the standard deviation of grain size distribution (SD), and 5.31% for DRX fraction. Additionally, the standard deviations of prediction error for these three parameters are 3.26% for AVG, 4.06% for SD, and 3.12% for DRX fraction. These results demonstrate that the multi-scale dynamic recrystallization model developed in this study exhibits satisfactory prediction accuracy and stability. The modeling approach presented in this paper is of great significance for precisely controlling the uniformity of microstructural distribution during the hot deformation of GH4706 alloy.

Materials doi: 10.3390/ma19163372

Authors: Chengqin Chen Wei Zhang Chenggui Chen Hongjuan Wu Rui Wang Xiaoyan Ma Xiaolei Wu

Fischer–Tropsch (FT) wax is widely used as an organic warm-mix asphalt (WMA) additive, lowering binder viscosity during construction while improving high-temperature deformation resistance in service; however, the comparative responses of SBS-modified asphalt to different FT wax grades remain insufficiently understood. Sasobit and three FT waxes with different carbon-chain ranges (FT 80, FT 90, FT 100) were incorporated into SBS-modified asphalt at about 7.0 wt%, and their effects on macroscopic performance, rheology, molecular packing, and diffusion were evaluated using physical-property tests, rotational viscosity, dynamic shear rheometer (DSR) testing, and molecular dynamics (MD) simulation. In the MD analysis, the wax additives were represented by linear alkane molecules with different chain lengths, and the systems were subjected to structural optimization, annealing, and NPT equilibration using the COMPASS III force field before the molecular descriptors were evaluated. The experimental results showed that all four additives produced a trade-off between increased high-temperature stiffness and reduced low-temperature ductility. Sasobit gave the strongest viscosity reduction (>70% above 165 °C), while FT 90 and FT 100 showed more stable, predictable viscosity–temperature behavior favorable for a wider construction window. DSR results showed higher complex modulus and lower phase angle for all modified binders at low frequencies, suggesting an increased elastic contribution and greater resistance to deformation under the tested rheological conditions; FT 80 produced the greatest stiffening but also the largest free volume and loosest molecular packing, whereas FT 100 increased cohesive energy density and reduced free volume, reflecting denser packing and stronger intermolecular cohesion. MD simulations revealed that FT wax enhanced short-time local molecular mobility and segment diffusion in its molten state (explaining the warm-mix viscosity reduction), whereas macroscopic stiffening and ductility loss at ambient temperatures were dictated by wax microcrystallization and physical network constraints that restricted long-range chain relaxation. By comparing three FT wax grades and Sasobit under the same experimental dosage and testing framework, this study provides a controlled assessment of the relationships among wax-grade characteristics, binder-scale rheological responses, and MD-derived molecular descriptors.

Materials doi: 10.3390/ma19163370

Authors: Weiwei Huang Guozheng Quan Hao Shi Yabing Duan Yu Wang Yawei Li Lin Yang Quanqiu Jiang Chunyu Mou Daojun Zhang Feng Ding Haitao Wang

Ultra-supercritical (USC) steam turbines combine severe steam conditions with increasingly frequent start-up, shutdown, and load-following operations. Their main steam valves must preserve pressure boundary integrity, sealing, and rapid actuation while non-uniform heating, creep, cyclic plasticity, oxidation, wear, and contact redistribution alter component geometry. However, the relevant evidence remains fragmented across alloy development, component thermo-mechanics, valve aerodynamics, and lifetime monitoring. This short, mechanism-oriented review integrates these domains through a material structure–function framework in which deformation relative to assembly clearance governs jamming risk. It synthesizes evidence on heat-resistant body and surface materials, 9–12% Cr steel stability, weldability and repair sensitivity, and cold, warm, and hot start-up histories. It also evaluates creep–fatigue interaction, contact, flow-induced vibration, multi-physics modeling, validation, uncertainty, monitoring, and digital twins. The synthesis shows that neither peak equivalent stress nor steady-state temperature alone can establish functional reliability. Credible assessment requires temperature-dependent material data, realistic steam-side heat transfer, cyclic constitutive behavior, initial and residual clearances, manufacturing and assembly tolerances, state-dependent friction, uncertainty analysis, and corroborating plant or inspection evidence. The most consequential research needs are valve-level validation datasets, thermal contact testing, function-oriented life criteria, and uncertainty-aware digital twins that jointly inform materials, geometry, and transient operation.

Materials doi: 10.3390/ma19163371

Authors: Alma Khassenovna Zhakina Oxana Vasilievna Arnt Yevgeniy Petrovich Vassilets Almat Maulenuly Zhakin Zainulla Muldakhmetov

A composite based on humic acid (HA) and reduced graphene oxide (rGO) was synthesized to evaluate the effect of rGO on the structural, functional, thermal, and preliminary phenol adsorption properties of humic acid. The incorporation of rGO increased the carbon content from 47.34 to 55.61 wt.% and decreased the oxygen content from 48.31 to 40.79 wt.%. At the same time, the total content of carboxyl and phenolic hydroxyl groups increased from 5.00 to 5.47 mmol/g, indicating improved accessibility of oxygen-containing functional sites. FTIR spectroscopy confirmed the retention of the main functional groups of the initial components after composite formation. Thermogravimetric analysis showed enhanced thermal stability, with the residual mass at 1000 °C increasing from 59.21 to 70.03%. Electron microscopy revealed the formation of a developed wrinkled surface morphology. Preliminary phenol adsorption experiments showed that the HA-rGO composite exhibited higher adsorption capacity than the initial HA and rGO. This improvement was attributed to the combined contribution of oxygen-containing functional groups and the aromatic carbon structure of rGO, which may promote hydrogen bonding and π–π interactions with phenol molecules.

Materials doi: 10.3390/ma19163368

Authors: Miglena G. Kirilova-Doneva Dessislava L. Pashkouleva

Hernia meshes are repeatedly subjected to physiological loading caused by fluctuations in intra-abdominal pressure during daily activities. This study aimed to investigate the effects of prolonged cyclic loading simulating repetitive severe coughing on the mechanical properties of expired, non-implanted Microval polypropylene mesh. Uniaxial cyclic tensile tests were performed on aged Microval mesh specimens in the two principal material directions. The loading protocol simulated repetitive coughing by applying six loading sessions per day over three consecutive days. Residual strain, elastic modulus, and loading duration were evaluated throughout the experiment. After the loading protocol, the specimens were tested to failure. Cyclic loading affected the mesh. Strain was within 12–20% in the longitudinal (L) direction and up to 25% in the transverse (T) direction after the third testing day. The elastic modulus increased significantly with repetitive loading, indicating pronounced material stiffening, while the ultimate tensile strength remained within the range measured for the unused specimens. In addition, the first loading cycle was approximately 20% longer than the subsequent cycles. Prolonged cyclic loading caused significant permanent deformation and pronounced material stiffening in the aged Microval mesh, whereas its ultimate tensile strength was only slightly affected. These findings enhance understanding of the mechanical behavior of hernia meshes under repetitive physiological loading.

Materials doi: 10.3390/ma19163369

Authors: Wenrui Xu Zichen Zhang Zhicheng Dong Hao Li Gaofeng Xie

High-water-content dredged clay is a water-rich sediment that requires sustainable, resource-oriented treatment, but conventional ordinary Portland cement (OPC) stabilization is hindered by excessive water-to-binder ratios, suppressed hydration, and high carbon emissions. This study investigated corn straw biochar (CSB) as a partial OPC substitute for the low-carbon stabilization of kaolin-based simulated dredged clay. CSB prepared at 200–1000 °C under different holding times was characterized by water absorption, thermogravimetry, and SEM. Clay specimens with an initial water content of 80% (1.5 wL) were prepared using 5–12% total binder, CSB:OPC ratios of 5:5–8:2, and curing ages of 7 and 28 d, and were evaluated by UCS, pH, SEM/ESEM, EDS, and life-cycle-based mechanical–environmental assessment. CSB developed honeycomb-like interconnected pores and a lamellar carbon skeleton, reaching 1476.10% water absorption at 700 °C for 30 min. The optimum CSB–OPC specimen reached approximately 136–137 kPa at 28 d, exceeding the OPC-only control of about 102 kPa. Strength improvement was associated with alkalinity maintenance, Ca–Si-rich hydration products, pore filling, and CSB–clay interfacial adsorption, embedding, and encapsulation. Properly carbonized CSB shows potential as an internal-curing, low-carbon co-binder for simulated dredged clay, but its field applicability requires further validation.

Materials doi: 10.3390/ma19163367

Authors: Nikolaos Alexopoulos Ioanna Giavrouta Leonard Alberty Max Horn Ismail Ünsal Georg Schlick

Cross-contamination during metal powder blending in multi-material laser powder bed fusion (PBF-LB/M) is a common production challenge and a key barrier to the wider industrial adoption of the process. In the present investigation, the effect of different CuCr1Zr foreign-particle cross-contamination rates of up to 5.0 wt.%, simulating different cross-contamination levels in an AlSi10Mg feedstock for PBF-LB/M, is examined. The resulting metallurgical features and tensile mechanical properties of the produced components were compared to those of reference specimens manufactured from uncontaminated powder. A microstructural analysis of CuCr1Zr contaminated samples revealed characteristic Cu-rich regions, demonstrating that the higher the level of cross-contamination is, the larger these regions are. Tensile yield stress is almost linearly increased with the contamination level while the opposite trend is noticed for tensile elongation at fracture. Two different stages of strain-hardening were noticed, with Stage I exhibiting a lower strain-hardening exponent, while higher strain-hardening exponents (>0.27) were noticed for Stage II, with the latter decreasing with increasing cross-contamination level. The tensile mechanical behaviour of PBF-LB/M specimens was evaluated for the first time with appropriate quality indices, which were initially developed for similar cast aluminium alloys. Overall, the quality index accounting for global tensile performance was decreased for all build directions with increasing cross-contamination level. Despite the lower quality index at the non-contamination level, the inclined (45°) printed specimens presented quality indices that were almost unaffected by the cross-contamination level.

Materials doi: 10.3390/ma19163366

Authors: Agnieszka Lipke Agnieszka Gładysz-Płaska Gabriele Klydziute Grzegorz Wójcik Renata Łyszczek Halina Głuchowska Ewa Skwarek Denis Sokol Marek Majdan Aivaras Kareiva

Layered double hydroxides (LDHs) are functional materials with tunable structural, surface, and adsorption properties. In this study, multicationic LDHs were synthesised and evaluated as adsorbents for chromate(VI). Among the investigated materials, the tetracationic Mg2Cu0.5Zn0.5Al1 composition exhibited consistently high mass-normalised Cr(VI) uptake in the screening experiments and was therefore selected for detailed investigation. Therefore, its chloride and carbonate forms were selected as model materials to examine the role of interlayer anions in Cr(VI) uptake and pH-dependent stability. The chloride form exhibited a higher adsorption capacity (70 mg/g) than the carbonate form (34 mg/g), indicating that more weakly bound interlayer anions may increase the accessibility of adsorption sites and promote anion exchange during adsorption. In contrast, the carbonate form showed greater structural stability, as confirmed by reduced cation leaching over a wide pH range. The behaviour of Cr(VI) in equilibrium solution was analysed as a function of its initial concentration, which allowed a simple description of Cr(VI) sorption over a wide range of initial pH values. XRD, FTIR, and XPS analyses supported partial interlayer anion exchange and changes in the coordination environment of surface metal centres after Cr(VI) sorption. Adsorption energies of 13–16.4 kJ/mol further suggested that Cr(VI) uptake cannot be assigned to a single interaction type but involves electrostatic interactions, anion exchange, and surface complexation. These results demonstrate that the interlayer anion is a key factor governing both the Cr(VI) adsorption efficiency and aqueous stability of LDH-based adsorbents.

Materials doi: 10.3390/ma19163365

Authors: Andrzej Jurecki Wojciech Grześkowiak Beata Klimek Marek Wieruszewski

Historic timber combines structural function with heritage value, yet its fire behaviour is inferred from contemporary wood data. This study provides an integrated, condition-based assessment of contemporary oak (Quercus robur L.) and historic oak from a nineteenth-century half-timbered building in Swołowo, Poland. Mass loss calorimetry (MLC) at 35 and 50 kW/m2 was combined with scanning electron microscopy (SEM) and SEM coupled with energy-dispersive X-ray spectroscopy (SEM–EDS). The aim was to determine whether surface preservation state explains differences between ignition sensitivity and cumulative heat release. Historic oak ignited earlier than contemporary oak, especially when the tested surface was degraded; at 50 kW/m2, time to ignition decreased from 25.33 s for contemporary oak to 18 s for non-degraded historic oak and 5.33 s for degraded historic oak. However, total heat release was lower for historic variants and final mass loss remained comparable. SEM showed roughness, fibrillation, delamination, fractured cell-wall edges and secondary porosity in aged and charred zones. SEM–EDS indicated C- and O-dominated preserved areas, whereas degraded and charred surfaces were enriched in inorganic elements. The results show that ignition propensity and total fire contribution should be evaluated separately, and that condition rather than age alone is critical for historic oak assessment.

Materials doi: 10.3390/ma19163364

Authors: Gerardo Gallegos-León Nelly Flores-Ramirez Salomon R. Vasquez-Garcia Leandro García-González José J. Contreras-Navarrete Lada Domratcheva-Lvova Julián Hernández-Torres José L. Rivera

Lignocellulosic waste materials (LWM), such as wood ash (WA) and sugarcane bagasse ash (SCBA), have emerged as promising alkali-activated precursors. In this study, WA- and SCBA-based matrices were modified with metakaolin (MK) and volcanic ash (VA) as complementary reactive precursors, while recycled expanded polystyrene (EPS) was incorporated as a lightweight modifier. Composites were prepared using a 15 M NaOH activator and characterized by compressive strength, Vickers hardness, and ball-on-disc tribological tests under dry sliding conditions to establish the relationship among precursor composition, mechanical behavior, and surface performance. SCBA-based composites exhibited higher compressive strength than WA-based systems, reaching 4.47 MPa in SCBA–VA formulations, whereas the hybrid WA–SCBA–VA formulation achieved the highest compressive strength (7.55 ± 0.25 MPa, n = 5). Although EPS reduced compressive strength, it increased surface hardness, with the highest value recorded for formulation 9BPS (25.4 HV). The WA–SCBA–VA formulation also exhibited the lowest wear rate (0.09 mm3/N·m), indicating superior tribological performance. Overall, VA was more effective than MK in enhancing the combined mechanical and tribological behavior of WA–SCBA-based composites. This study provides a systematic comparative assessment of the tribological performance of lignocellulosic ash-based alkali-activated composites, offering new insights into the relationship between precursor composition and surface performance in lightweight sustainable materials.

Materials doi: 10.3390/ma19163363

Authors: Yujie Wang Lingzhi Li

Featuring considerable tensile ductility and multiple cracking behavior, polyethylene fiber-reinforced engineered cementitious composites (PE-ECCs) are promising cement-based materials for engineering construction. However, establishing accurate design models for evaluating the mechanical properties of PE-ECC is a challenging task owing to the complex material components. This study presents an interpretable data-driven framework for predicting the mechanical properties of PE-ECC using mixture-of-experts (MoE) learning. A database comprising 383 deduplicated material-level records from 90 verified literature sources was compiled for modeling the compressive strength, ultimate tensile strain, ultimate tensile strength and first-cracking tensile strength of PE-ECC. An MoE prediction model was developed by integrating XGBoost, LightGBM, CatBoost, WDBPANN and TabPFN through out-of-fold stacking and learned gating. The model achieved coefficient of determination (R2) values of 0.971, 0.950, 0.970 and 0.954 for the four mechanical properties, respectively. Shapley additive explanations (SHAP), accumulated local effects (ALE) and response maps were used to examine the fitted nonlinear associations between the reported mixture variables and each target property. Based on these relationships, support-filtered virtual screening was conducted within the database-supported design space to identify candidate mixtures for subsequent experimental verification. The framework links target-specific prediction with mixture-response interpretation and confines screening to regions supported by reported PE-ECC mixtures.

Materials doi: 10.3390/ma19163362

Authors: Zhonglan Hou Yibo Zhang Pengyan Guo Mohammad Hossein Yazdi Perk Lin Chong Fuwang Zhou Haining Bu Xiao Zhu Jie Shen Zhen Zhang Yuguo Gao

Side-boss parallel channels can enhance reactant transport and water removal in proton exchange membrane fuel cells, but their local protrusions increase the forming difficulty of ultra-thin metallic bipolar plates. This study numerically investigates the single-step stamping formability of 0.1 mm SS304 bipolar plates using Dynaform. The effects of side-boss number, side-boss height, and punch speed were evaluated through thickness distribution, maximum thinning ratio, and forming-limit-diagram states. The results show that side-boss height is the dominant geometric factor. Increasing the height from 0 to 0.75 mm raises the maximum thinning ratio from 17.69% to 29.87% and shifts the critical deformation regions from the conventional channel bottom toward the side-boss roots, boss tops, transition fillets, and channel corners. The number of side-boss sets produces a non-monotonic thinning response, with maximum thinning ratios ranging from 19.54% to 27.76% for the modified configurations. Punch speeds of 200, 500, and 800 mm/s yield comparable thinning levels of 24.60%, 23.09%, and 23.16%, respectively, whereas the value increases to 26.30% at 1100 mm/s. Under the present forming conditions, these findings establish a quantitative relationship between side-boss geometry, material-flow restriction, and strain localization, and provide practical guidance for geometry selection and stamping-process design of metallic bipolar plates.

Materials doi: 10.3390/ma19163361

Authors: Juanli Wang Ye Tian Jiayao Tian Qingyang Xie

Longhu Pagoda, a national key cultural heritage site located at the southern foot of Hushan Mountain in Liubao, Jinan, Shandong Province, is a masterpiece of Tang-dynasty stone pagoda architecture and a core component of the Shentong Temple heritage complex alongside the Four Gates Pagoda. The pagoda features a distinctive “Tang-dynasty body, Song-dynasty crown” structure: its stone base and main body, carved with intricate high-reliefs of dragons, tigers, heavenly kings, arhats, and apsaras, date back to the late Tang Dynasty (717–845 AD), while the brick eaves and roof were reconstructed during the Northern Song Dynasty. Severely threatened by biodeterioration induced by bryophytes, lichens, and associated microorganisms, the pagoda’s exquisitely carved stone surface has undergone irreversible aesthetic degradation and structural weakening, threatening its thousand-year-old artistic integrity. Biocide treatment is a commonly adopted strategy for stone heritage conservation. This study aims to characterize the specific biodeteriogens colonizing Longhu Pagoda and evaluate the efficacy of various biocides for targeted conservation intervention. In this study, biological samples collected from Longhu Pagoda were first identified: bryophyte samples contained chloroplasts, with some having morphological characteristics similar to Pottiaceae or Grimmiaceae; symbiotic algae isolated from lichen samples were identified as Chlorella sp.; four dominant fungal strains were isolated via morphological observation and molecular sequencing (ITS), namely Aspergillus niger (F1), Trichoderma yunnanense (F2), Talaromyces ruber (F3), and Aspergillus aflatoxiformans (F4). On this basis, the inhibitory effects of different biocides on dominant deteriorating organisms were systematically evaluated via chlorophyll fluorescence analysis, algal growth inhibition tests, and oxford cup assays, combined with field verification on Longhu Pagoda. The optimal biocide with stable inhibition efficacy and favorable stone compatibility was screened out. The results provide technical support for the biological conservation of Longhu Pagoda and similar stone cultural relics suffering from microbial biodeterioration.

Materials doi: 10.3390/ma19163360

Authors: Andrzej Pacana Miłosz Pilch Małgorzata Ulewicz

The circular economy increases the importance of quality and traceability in functional materials produced from industrial, municipal, and agricultural waste. However, the selection of Industry 4.0 (I4.0) technologies in waste valorization remains unsystematic and weakly linked to material and process requirements. This study develops a decision-support model for selecting I4.0 solutions for quality assurance and traceability in the production of waste-derived functional materials. The model was grounded in a two-track scoping review reported according to PRISMA-ScR. Track A mapped the functions of I4.0 technologies in quality control and manufacturing traceability, while Track B identified challenges related to waste-derived biopolymers, composites, sorbents, catalysts, and nanomaterials. Among 322 primary material studies, microstructure, morphology, and porosity dominated (69.9%), whereas traceability was underrepresented and requires further validation. In Track A, 629 studies were unambiguously mapped, with inspection and monitoring as the dominant functions. Material-specific challenges were then linked to required functions and candidate technologies, which were ranked by their fit to the decision situation and literature support. The resulting model covered 48 material situations and 95 function–technology pairs. It supports technology selection based on material category, waste type, process stage, and quality or traceability requirements rather than technology availability alone. The proposed approach may be extended to waste-derived materials for other application sectors, including construction and transport, subject to sector-specific, material-specific, and industrial validation.

Materials doi: 10.3390/ma19153359

Authors: Die Xu Shanshan He Jingzhu Xing Li Hao Zhijun Zhang Miao Su

The complexity and heterogeneity of tumors make monotherapy inadequate for effective tumor elimination, highlighting the urgent need for multifunctional synergistic therapeutic strategies. In this study, a near-infrared (NIR)-responsive multimodal therapeutic nanoplatform (FSINPs) was constructed by simple adsorption of indocyanine green (ICG) and Fe3+ onto silk fibroin nanoparticles. Molecular docking showed that ICG binds stably to silk fibroin mainly via hydrogen bonds. Density functional theory (DFT) calculations predicted that Fe3+ strongly coordinates with the sulfonate groups of ICG and quenches ICG fluorescence via intermolecular charge transfer. Under conditions mimicking the acidic and high-glutathione tumor microenvironment, the ICG-Fe3+ coordination is disrupted, leading to fluorescence recovery of FSINPs. Fe3+ catalyzes the Fenton reaction to generate hydroxyl radicals (·OH), thereby achieving chemodynamic therapy (CDT). Upon 808 nm laser irradiation, ICG acts as a dual photosensitizer capable of both photothermal therapy (PTT) and photodynamic therapy (PDT), generating local hyperthermia with a photothermal conversion efficiency as high as 48.7% and producing singlet oxygen (1O2). The photothermal effect facilitates ·OH production, and CDT enhances photodynamic efficacy. The synergistic action of the three therapeutic modalities results in potent light-activated cytotoxicity toward tumor cells. In vivo experiments demonstrated that FSINPs enable tumor microenvironment-responsive fluorescence imaging for over 48 h and achieve complete tumor eradication in a 4T1 tumor model without obvious systemic toxicity. This study provides a new strategy for constructing activatable imaging and highly synergistic PTT/CDT/PDT-integrated silk fibroin-based nanomedicines and offers computational chemistry references for their rational design and development.

Materials doi: 10.3390/ma19153358

Authors: Mohamed N. Omar Mustafa Batikha Md Azher Uddin

3D Concrete Printing (3DCP) has emerged as a transformative construction technology, offering enhanced design flexibility, reduced material waste, improved construction efficiency, and safer working environments. Despite these advantages, the absence of standardised design provisions for structural 3DCP elements remains a major obstacle to its widespread adoption. This study develops statistical and machine learning models to predict the design strengths of hardened 3D-printed concrete. A comprehensive database of experimental results published between 2012 and 2025 was compiled and analysed, encompassing the compressive, flexural, and shear strengths of hardened 3DCP materials. Regression-based statistical modelling was employed to derive design strength equations and assess their consistency with conventional concrete design approaches. In parallel, several machine learning algorithms were developed using the same dataset to benchmark predictive performance and evaluate the robustness of the proposed statistical models. The statistical models achieved good predictive accuracy for compressive and flexural strengths, with coefficients of determination (R2) of 0.83 and 0.67, respectively. By contrast, the shear strength model exhibited greater variability (R2 = 0.39), reflecting the limited availability and considerable scatter of published experimental data. Benchmarking against the optimised machine learning model demonstrated excellent agreement with the proposed statistical equations, yielding coefficients of determination of 0.93 and 0.94 for compressive and flexural strengths, respectively. The proposed modelling framework provides preliminary design strength predictions for hardened 3D-printed concrete, contributing to the development of robust structural design guidelines and facilitating the wider adoption of 3DCP in construction practice.

Materials doi: 10.3390/ma19153357

Authors: Haitao Wang Jiabao Liu Liu Yang Kai Liu Shujie Niu Yuanyuan Wang

The semi-underground granary is a new type of energy-saving grain storage facility that can use shallow geothermal energy to reduce energy consumption during grain storage. However, unclear temperature fields and the lack of grain pile temperature control methods are not conducive to the design and application of semi-underground granaries. In this study, the temperature fields and temperature control methods for grain piles in a semi-underground granary were numerically investigated by using an experimentally verified COMSOL model and a collaborative simulation method combining steady-state heat transfer and dynamic heat transfer. Multiple grain storage temperature control methods for the semi-underground granary were presented to improve grain storage safety, including an intermediate floor slab, an embedded-pipe wall, floor burial depth, and envelope insulation. The results showed that there was significant spatial heterogeneity in the temperature field distribution of the grain pile in the semi-underground granary. The large thermal inertia of the soil and the stable low-temperature soil environment reduced the influence of outdoor air temperature variations on the grain pile temperature field. Installing an intermediate floor slab could achieve natural low-temperature grain storage in the underground section of the semi-underground granary. An embedded-pipe wall could effectively solve the problem of local temperature increases in grain piles caused by heat transfer through the granary walls. The floor burial depth of the semi-underground granary was a key influencing factor of heat transfer through the granary wall. Granary wall thickness had a significant impact on the thermal performance of the walls and the grain pile temperature field due to changes in wall insulation. These results can provide beneficial suggestions for guiding the design of grain storage temperature control methods in semi-underground granaries.

Materials doi: 10.3390/ma19153356

Authors: Michelle Tinotenda Nyambi Chunhua Lu Wenshuo Li Weiqi Zhang

Concrete is fundamentally susceptible to cracking, which creates pathways for aggressive agents, accelerating reinforcement corrosion and reducing service life. Traditional repair methods are ineffective for micro-cracks and generate volatile compounds. Microbially induced calcium carbonate precipitation (MICP) offers a sustainable bio-based alternative that catalyses in situ calcium carbonate (CaCO3) precipitation within cracks, sealing pathways. This study compares two MICP repair systems consisting of Sporosarcina pasteurii (SP, ureolytic) and Bacillus mucilaginosus (BM, non-ureolytic), utilising a dual-viscosity-modifying-agent (VMA) system comprising Welan Gum and Attagel 50 (WA). The repair treatments were applied externally on cracked concrete specimens across crack widths of 0.10–0.80 mm for 16 days. Crack repair effectiveness was evaluated through splitting tensile strength, capillary water absorption, rapid chloride migration (RCM), and X-ray diffraction (XRD). SP + WA exhibited high performance trends compared with BM + WA, achieving tensile strength retention of 59.57–68.95% vs. 56.68–67.15%, capillary water absorption recovery ranges of 58.36–64.81% vs. 51.71–58.02%, chloride resistance recoveries of 82.1–63.7% vs. 50.5–60.0%, and DRCM recoveries of 57.35–77.68% vs. 46.04–61.00% relative to intact controls. Durability recovery efficiency decreased with increasing crack width. XRD confirmed calcite as the sole CaCO3 polymorph in both systems, with sharper peaks in SP + WA indicating differences in calcite crystal characteristics, while BM + WA produced broader peaks similar to a nanocrystalline CaCO3 structure. These findings demonstrate that the dual-VMA-assisted MICP approach potentially improves mechanical and durability properties in cracked concrete, with ureolytic SP demonstrating better repair performance trends.

Materials doi: 10.3390/ma19153355

Authors: Milos Poliak Piotr Czyzewski Przemyslaw Kubiak Damian Frej Adam Rylski Marek Wozniak Krzysztof Siczek

Magnesium (Mg) alloys are crucial for lightweight automotive design, underscoring the need for effective welding despite their poor weldability and susceptibility to defects such as cracks. The paper was prepared by reviewing available scientific databases of studies and patents using appropriate keywords. It reviews the properties, applications, and welding methods (fusion, friction, diffusion, explosive, and hybrid) of Mg alloys, assessing their advantages, disadvantages, and precautions. The importance of understanding the mechanical behavior and structural integrity of welded joints was highlighted. The impact of process variables on weld microstructure and properties, along with future research areas, is also addressed. AZ-series Mg alloys were found to be favored for weldability. For them, primary welding methods include GTAW, GMAW, LBW, and FSW. Trends emphasize solid-state techniques, advanced dissimilar metal joining, and AI optimization to enhance welding efficiency and quality. Welding of modern Mg-inclusive high-entropy alloys is under intensive development.

Materials doi: 10.3390/ma19153353

Authors: Elżbieta Stanaszek-Tomal

Natural fibre-reinforced polymer biocomposites are increasingly considered for construction applications because of their renewable reinforcement, low density and potentially reduced environmental impact. Their durability, however, is strongly constrained by moisture, which promotes fibre swelling, weakens the fibre–matrix interphase and creates conditions favourable to fungal colonisation. This review examines the effects of moisture and biodeterioration on the structural and thermal performance of natural fibre-reinforced polymer composites used in construction. Across the reviewed studies, moisture and hygrothermal ageing produced tensile-strength reductions ranging from less than 10% to approximately 40%, while losses in stiffness or impact performance exceeded 40–70% in particularly susceptible systems. In contrast, directly comparable quantitative data linking fungal biodeterioration with changes in thermal conductivity remain scarce, representing a major research gap. Current durability standards, particularly ISO 846:2019, provide useful screening data but do not fully reproduce the cyclic hygrothermal conditions experienced by porous, hygroscopic construction biocomposites. More reliable durability assessment requires integrated microbiological, hygrothermal, mechanical and microstructural testing supported by advanced non-destructive diagnostics. Protection strategies should combine moisture control and biological resistance while considering long-term service performance, environmental impacts, recyclability and end-of-life constraints.

Materials doi: 10.3390/ma19153354

Authors: Jakub W. Narojczyk Krzysztof W. Wojciechowski Konstantin V. Tretiakov

Predicting how atomic-scale structural changes influence a system’s elastic properties is challenging in general. In this study, we examined how the reduction in the atomic degrees of freedom within layer inclusions embedded in a hard-sphere crystal affects its auxetic behaviour. This reduction was achieved by randomly pairing the neighbouring hard spheres into diatomic molecules called dumbbells. Specifically, we explored the effects of periodically introducing one-, two-, and three-layer inclusions of dumbbells on the crystal’s elastic properties. Our results show that inclusions of adjacent layers filled with dumbbells notably alter the elastic behaviour compared to systems with similar inclusions composed of spheres. We observed that by rigidly connecting neighbouring spheres to form diatomic molecules within inclusion layers, two opposing effects can be achieved. First, at slightly smaller diameters of the spheres forming dumbbells, we found an enhancement of auxetic properties in comparison with the system containing only hard spheres. Second, for systems with large sphere diameters forming dumbbells, we observed that the crystal’s auxetic properties were almost eliminated.

Materials doi: 10.3390/ma19153352

Authors: Zhengang Yuan Xuefeng Xu Jiaqi Huang Jun Xie Fengwei Zhang Kai Tian

To address the challenges of procedural complexity, the lack of an integrated heating–forming capability, and poor formability in the hot forming of titanium alloy skin components, an electrically assisted forming (EAF) process is proposed. A Johnson–Cook constitutive model was established to characterize the flow behavior of Ti–6Al–4V alloy under electric-assisted conditions, achieving a correlation coefficient of 0.968 and an average relative error of 7.67%. Forming parameters were investigated through a combined approach of numerical simulation and experimentation. At a current density of 7.59 A/mm2, a forming speed of 1 mm/min, and a friction coefficient of 0.1, the maximum springback of the component was 1.04 mm. Compared with isothermal forming, the EAF process reduced the springback by 7.14% and enhanced the ultimate tensile strength by 5.34%. Microstructural characterization revealed that, under pulsed current, the α-phase grains of the material were refined, whereas the β-phase fraction and the average grain size increased, accompanied by a 15.3% reduction in the geometrically necessary dislocation (GND) density. This study validates the process feasibility of electrically assisted forming for thin-walled titanium alloy skin components.

Materials doi: 10.3390/ma19153351

Authors: Konstantin V. Khishchenko

This work is devoted to the description of the thermodynamics of the condensed states of the rare-earth metal europium under intense mechanical and thermal loading in shock waves. A new model of the equation of state for metallic materials is proposed based on the characteristic function of entropy with volume and internal energy (per unit mass) as variables. Within the framework of this model, calculations of the thermodynamic characteristics of europium at high pressures and specific entropies were carried out, the results of which are presented in comparison with the available data from shock-wave experiments. The developed equation of state for this material can be effectively applied to the modeling and simulation of various dynamic processes at high energy densities.

Materials doi: 10.3390/ma19153350

Authors: Jiashun Gao Liehua Liu Zhilong Xu Jiang Zhu Zhijie Hu Hongxin Lin

The influence of tempering temperature on the microstructure evolution and mechanical properties of 1Cr12Ni2WMoVNb martensitic stainless steel was systematically investigated in the range of 200–650 °C. Microhardness, tensile strength, and impact toughness were evaluated, combined with analyses using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and phase characterization techniques. The results show that hardness and tensile strength initially decrease, then increase to a peak at approximately 550 °C due to secondary hardening, and finally decline significantly. In contrast, impact toughness exhibits an inverse trend, revealing a clear strength–toughness trade-off. Microstructural analysis indicates that this behavior is governed by the competition among multiple strengthening mechanisms. At intermediate temperatures, the precipitation of fine and dispersed M23C6 carbides leads to strong dislocation pinning and pronounced precipitation strengthening, resulting in peak strength but reduced plastic deformation capability. At higher temperatures, carbide coarsening and dislocation recovery weaken strengthening while restoring plasticity, thereby improving toughness. These findings clarify the temperature-dependent competition among strengthening mechanisms governing the strength–toughness evolution during tempering.

Materials doi: 10.3390/ma19153349

Authors: Puspitasari Jaehyeong Kim Rajalingam Agneeswari Jae-Hoon Lee Suhee Song Won-Ki Lee Wang Yong Yang Jin Young Kim Youngeup Jin

A series of donor–acceptor π-conjugated polymers based on Difluorophenazine acceptor and benzodithiophene donor units with different substituents, hydrogen (H), chlorine (Cl), fluorine (F), and sulfur (S), was designed and synthesized to investigate how donor-side substituent modification influences optoelectronic properties. The substituent variation systematically modulated the optical band gaps (1.72–1.82 eV) and HOMO energy levels (−5.42 to −5.58 eV). When applied in bulk heterojunction solar cells with the Y6 acceptor, these polymers delivered power conversion efficiencies ranging from 3.85% to 7.79%. The fluorinated polymer P(BDTTF-TffPzT) exhibited the best performance, with Jsc = 19.65 mA cm−2, Voc = 0.825 V, and FF = 0.481. These findings establish that donor-side substituent engineering is an effective molecular design strategy for tuning optoelectronic properties and device performance in phenazine-based polymer systems.

Materials doi: 10.3390/ma19153348

Authors: Zhien Ning Xu Ji Wei Zhang Jijun Yang Linjiang Chai

The effect of internal pressure on the layered microstructural evolution of N36 zirconium alloy cladding tubes was systematically studied under simulated loss-of-coolant accident (LOCA) biaxial creep conditions at 900 °C. The tested specimens were characterized by electron channeling contrast imaging, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, and transmission electron microscopy. The results show that all specimens formed a typical layered cross-sectional structure consisting of an oxide film, an oxygen-rich α-Zr (α(O)) layer, and a prior-β transformed layer. The thickness of the α(O) layer and the oxygen diffusion depth changed markedly with internal pressure. The thickness of the α(O) layer was approximately 21 μm for the 0.8 MPa specimen and 11 μm for the 1.9 MPa specimen, respectively. The lower-pressure specimen exhibited a wider oxygen-affected region, whereas the higher-pressure specimen showed a steeper oxygen gradient. In the prior-β transformed layer, lath-like α structures formed under both conditions, but their spatial arrangement and orientation distribution were different. Under lower internal pressure, the laths were more regularly arranged and showed a more complete colony structure. Under higher internal pressure, the laths were more interwoven, and the orientation distribution became more scattered. Meanwhile, the high-pressure specimen retained a higher local orientation gradient and a higher degree of lattice distortion. These results indicate that the above microstructural differences mainly arise from the effect of internal pressure on the high-temperature exposure history. A higher internal pressure causes earlier instability of the specimen, thereby shortening the effective time for oxygen diffusion and microstructural evolution, rather than directly changing the oxidation or phase transformation process.

Materials doi: 10.3390/ma19153347

Authors: Vinoth Nageshwaran Sudhir Amritphale Soundararajan Ezekiel

Portland cement production accounts for roughly 8% of anthropogenic CO2 emissions, driving interest in low-carbon geopolymer binders. One-part (“just-add-water”) geopolymers, which replace hazardous liquid activators with a dry, pre-blended solid activator, are especially suited to field deployment where handling safety and logistics are decisive. However, their formulation space is combinatorially vast, and trial-and-error development cannot efficiently navigate it. This paper reviews one-part geopolymer science, presents a new comparative and interpretable ML analysis of a published 80-mixture one-part fly-ash/ground granulated blast-furnace slag (GGBS, hereafter slag) geopolymer dataset from twelve studies, and proposes an AI-assisted design framework. The ML demonstration targets 28-day compressive strength only. Under leave-one-source-out (LOSO) cross-validation—the appropriate test for a literature-pooled dataset—gradient-boosted trees achieved R2 = 0.61 (RMSE = 15.5 MPa; 95% bootstrap confidence interval on R2, 0.44–0.75), well above a linear baseline (0.36), suggesting that non-linear structure transfers across studies; a random split gives a higher but less reliable R2 = 0.90 on only 16 test mixtures. Because fly-ash and slag contents are near-perfectly anti-correlated (r=−0.99), we model the precursor axis as a single slag fraction descriptor; SHAP then identifies this precursor balance and the activator’s Na2O dosage as the dominant statistical predictors of strength in this dataset, an ordering consistent with known activation chemistry; causal confirmation of these associations awaits the experimental validation stage of the proposed framework. Demonstrated for strength only, at paste level, the framework offers a transferable route toward multifunctional low-carbon binders for protective and infrastructure applications; the multifunctional extensions are proposed, but not yet demonstrated.

Materials doi: 10.3390/ma19153346

Authors: Junhui Yao Jianyuan Jin Yin Chen Zulyar Ilxat Hui Chen

Reducing cement consumption in mine backfill materials and improving the synergistic utilization of multi-source solid wastes are important for developing low-carbon backfill systems. In this study, fly ash–carbide slag–bentonite-based whole-tailings backfill (FCB) was optimized using a Box–Behnken response surface design. The effects of replacement ratio, FA/CS ratio, and bentonite content on fluidity, setting time, and 28 d uniaxial compressive strength were investigated, and the microstructural mechanism was analyzed by XRD and SEM. The results show that all quadratic models are statistically significant, with the strength model exhibiting the best fitting and predictive performance. The replacement ratio and bentonite content are the main factors affecting FCB performance, while the FA/CS ratio plays a secondary role. Strength decreases with increasing replacement ratio, whereas bentonite content shows a quadratic effect on fluidity and strength. Multi-objective optimization gives an optimal mix of A = 0.58, B = 2.71, and C = 4.99%, with validation errors below 5%. XRD and SEM results indicate that C-(A)-S-H gel and AFt are the main hydration products. Lower replacement ratios and appropriate bentonite contents were associated with a more continuous matrix morphology in the selected SEM regions and higher compressive strength.

Materials doi: 10.3390/ma19153345

Authors: Binbin Li Jun Tan

Mg/Al laminated metal composites (LMCs) combine the low density of Mg alloys with the good corrosion resistance and formability of Al alloys, showing great application potential in the lightweighting field. However, the difficulty in coordinating deformation between Mg and Al alloys, together with the inevitable formation of brittle Al-Mg intermetallic compounds (IMCs) at the interface when the two metals are directly bonded, severely deteriorates the mechanical properties of Mg/Al LMCs and hinders their transition toward practical engineering applications. This perspective systematically reviews the historical development and primary fabrication routes of Mg/Al LMCs, with a particular focus on the thermodynamics and kinetics of interfacial reactions, the shift from passive IMC suppression to active interfacial-phase design, and the emerging opportunities brought by artificial intelligence. Furthermore, the remaining challenges in process–interface–property correlations, multicomponent interlayer design, database construction for AI-driven design, and closed-loop intelligent manufacturing are identified. The aim is to guide future research through critical insights and perspectives, and to offer valuable references for the development of high-performance lightweight LMCs.

Materials doi: 10.3390/ma19153344

Authors: Zeshen Jiang Zhou Zhou Xingyu Gu

This study examines how reclaimed asphalt pavement (RAP) dosage, virgin-binder grade, and virgin-binder content govern the cracking response of Marshall-designed mixtures. The experimental matrix comprised four RAP levels (30%, 40%, 50%, and 60%), two modified virgin binders (PG 76-22 and PG 88-34) evaluated at their respective optimum asphalt contents (OACs), and two binder-rich PG 76-22 variants (OAC + 0.3 and OAC + 0.5 percentage points); virgin mixtures served as controls. Cracking behavior was characterized by low-temperature semi-circular bending (SCB), the Illinois Flexibility Index Test (I-FIT), and direct-tension cyclic fatigue (DTCF). Fracture and fatigue indicators were subsequently integrated into cracking balance design diagrams, and k-means clustering was used to derive provisional, dataset-specific performance boundaries for long-term oven-aged mixtures. The results show that the higher-performance binder improved long-term cracking resistance at moderate RAP contents. By contrast, mixtures with 50% or 60% RAP and PG 76-22 displayed a distinctly brittle response. Increasing the PG 76-22 content above OAC produced only limited gains. These findings demonstrate that binder quality, rather than a small increase in binder dosage, is the more effective lever for balancing fracture and fatigue resistance in mixtures with substantial RAP contents.

Materials doi: 10.3390/ma19153343

Authors: Hui Li Xiangkun Song Qing Tao Zhenqian Wang Qiulai Huang Weipeng Xu Qingliang Li Jian Wang

High-carbon martensitic steels for bearing components are conventionally low-temperature tempered for stress relief, yet the influence of tempering temperature on compressive and fatigue wear resistance remains unclear, directly affecting the service life of bearing races and rollers. In this study, a high-carbon martensitic steel was tempered at 170 °C, 200 °C, and 230 °C. The microstructural evolution, compressive properties, and contact fatigue wear resistance were systematically investigated, along with the corresponding strengthening and wear mechanisms. After spheroidizing annealing and quenching, the microstructure consists of high-carbon martensite and retained austenite, with a high density of dislocations and fine twins. Tempering decomposes retained austenite into tempered martensite and promotes fine carbide precipitation, processes that become more pronounced at higher temperatures. Consequently, hardness decreases from 810 HV in the as-quenched state to 690 HV after 230 °C tempering, while compressive failure strain increases from 10.5% to 24.1%. More importantly, under cyclic contact stress, the 230 °C-tempered specimen exhibits approximately 33% lower wear mass loss than the 170 °C-tempered counterpart, despite its lower hardness. This unexpected improvement is attributed to the formation of a distinct plastic deformation zone in the near-surface region, which absorbs greater strain energy and delays fatigue spallation. The well-tempered martensitic matrix accommodates more long-range dislocation slip, enabling a transition from fatigue spallation to a more ductile failure mode. These findings provide new insights into the role of low-temperature tempering in balancing strength, ductility, and wear resistance, and offer practical guidance for optimizing heat treatment protocols to enhance the contact fatigue performance of bearing steels.

Materials doi: 10.3390/ma19153342

Authors: Yuze Li Jiayi Zhao Qifeng Liu Xiaoyang Chen Haiwei Zhang Kairong Jin Wei Wang Peng Yin Tingting Zhang

This study investigated the resistance of recycled aggregate concrete (RAC) to chloride penetration under freeze-thaw cycles using both numerical simulation and experimental validation. A five-phase mesoscale model of RAC was developed. The salt freeze-thaw test was conducted to validate the simulated values and explore the effects of different recycled coarse aggregate (RCA) substitution ratios, as well as varying dosages of fly ash and superfine fly ash, on chloride concentration in RAC. The experimental data showed satisfactory agreement with the simulated values, confirming the model’s validity. Additionally, the RCA volume fraction, interfacial transition zone (ITZ) thickness, and adhesive ratio of old mortar were analyzed using simulation. The variation patterns of compressive strength, relative dynamic elastic modulus, and mass loss of RAC also revealed the mechanisms by which RCA substitution ratio and the dosages of fly ash and superfine fly ash act under salt freeze-thaw conditions. This study provides guidance for enhancing the resistance of RAC to chloride penetration and its durability under freeze-thaw conditions.

Materials doi: 10.3390/ma19153341

Authors: Qinmiao Yu Jinglan Liang Xueji Chang Xiaojuan Xia Jiang Zhao

The optoelectronic properties of the lead-free perovskite CsSn0.5Ge0.5I3 are investigated by first-principles calculations and numerical simulations using SCAPS-1D. The energy-level alignment between transport layers and the perovskite layer is evaluated, resulting in the establishment of the PCBM/CsSn0.5Ge0.5I3/PEDOT:PSS structure. Key parameters, including bulk defect density, layer thickness, and electrode materials, are optimised, and the effects of resistance, illumination intensity, thermal stability, and carrier generation-recombination rates on device performance are analysed. The optimal device structure FTO/PCBM/CsSn0.5Ge0.5I3/PEDOT:PSS/C achieves a power conversion efficiency (PCE) of 24.50% and a fill factor (FF) of 80.01%. Machine learning (ML) algorithms are applied to predict photovoltaic parameters, with Random Forest (RF) exhibiting the highest accuracy. SHAP analysis identifies absorber layer thickness as the dominant factor influencing efficiency, providing guidance for experimental optimisation. This integrated approach offers a practical pathway for designing high-performance, stable, and environmentally sustainable perovskite solar cells (PSCs).

Materials doi: 10.3390/ma19153340

Authors: Qiang Li Xuefeng She Guang Wang Qingguo Xue Haibin Zuo Jingsong Wang

To optimize the configuration of low-carbon blast furnace raw materials and fuels, this study systematically evaluated the reaction initiation temperature, solution loss degradation, ferrous burden softening–melting behavior, and gas permeability of different reactive cokes under four simulated atmospheres: a traditional blast furnace (TBF), a hydrogen-rich traditional blast furnace (TBF-H2), an oxygen blast furnace (OBF), and a hydrogen-rich oxygen blast furnace (OBF-H2). The results show that with increasing coke reactivity, enhanced early reduction leads to a decrease in the softening initiation temperature, dropping from 1089 to 1074 °C under the traditional blast furnace atmosphere. In hydrogen-rich atmospheres, high concentrations of H2O significantly reduce the proportion of optically anisotropic structure—which characterizes coke strength—from 61.0% to 41.7%, indicating intensified degradation and fragmentation of the load-bearing coke structure. Process adaptability evaluations reveal that under the TBF atmosphere, burden-column permeability is highly sensitive to coke reactivity, with Coke 3 causing the maximum pressure drop (ΔPmax) to increase to 35.7 kPa, indicating the need for high-quality coke. Conversely, under OBF and OBF-H2 processes, the high reduction potential compresses the melting zone to a narrow range of 10–30 °C, maintaining both ΔPmax (11.5–14.0 kPa) and the cohesive-zone permeability index S (<150 kPa·°C) at consistently low levels. Within the present laboratory apparatus and the three-coke dataset, the oxygen-blast-furnace atmospheres reduced the sensitivity of cohesive-zone permeability to coke reactivity. This result suggests a potentially broader coke-quality window, but pilot-scale validation, process simulation, and economic assessment are required before industrial application or cost advantages can be established.

Materials doi: 10.3390/ma19153339

Authors: Kun Ren Julong Yuan Hua Li Qing Miao Zhongwang Wang Qing Liu Xiang Liu

Hard and brittle material components with complex curved surfaces are widely used in critical foundational parts within aerospace, optoelectronics, and other fields. Their machining quality directly determines the performance and reliability of high-end equipment. However, the inherent properties of hard and brittle materials make them prone to surface/subsurface damage during traditional polishing processes, and maintaining the form accuracy of complex curved surfaces is challenging. Although abrasive waterjet polishing enables non-contact flexible processing, its energy efficiency is low. Additionally, although ultrasonic-assisted polishing can improve material removal, its spatial localization is insufficient, limiting energy utilization efficiency. To address these issues, this paper proposes a novel method of focused, ultrasonic, vibration-assisted abrasive waterjet polishing. The influence of the radiation force and cavitation force of the focused ultrasonic field on abrasive particle motion is analyzed, and analytical equations for abrasive particle velocity are established. Subsequently, single-factor and response surface methodologies are employed to systematically evaluate the influence of process parameters on machining quality and efficiency. The material removal process during FUAP involves both plastic shearing/chip formation and localized brittle fracture. Focused ultrasonic assistance promotes micro-cutting and plastic shearing, while localized crushing pits indicate that brittle fracture remains non-negligible. The focused ultrasound superimposes alternating stress onto the impact action, mitigating microscale crushing pit defects during the brittle removal process of monocrystalline silicon. Furthermore, appropriately increasing ultrasonic power, enlarging abrasive particle size, and raising abrasive concentration all contribute to enhanced material removal from monocrystalline silicon. Adjusting the nozzle height to the effective region of the focused ultrasonic energy field promotes material removal via chip formation while avoiding pit defects caused by excessive fracture. These results suggest that focused ultrasonic energy can be effectively integrated into abrasive waterjet polishing to enhance material removal while suppressing brittle surface defects, thereby offering a promising strategy for the ultra-precision finishing of hard and brittle components with complex curved surfaces.

Materials doi: 10.3390/ma19153338

Authors: Andrzej Ubysz Konrad Łuszczyk Dominik Logoń Aleksandra Ubysz Jarosław Rybak

This paper presents the possibilities of using steel cord from car tires as a structural concrete reinforcement obtained after initial mechanical treatment. The steel wire constituting tire reinforcement after mechanical separation from rubber is not further processed and, in the form partially contaminated with rubber, is stored in landfills. Further processing is usually not economically justified. The purpose of the work is to determine the physical properties of fiber concrete, made of ordinary concrete with the addition of steel fibers recovered from tires, obtained in the process of relatively easy recycling. The work is mainly experimental. The literature review presents the basics of the current state of knowledge regarding the methods of making and testing elements made of fiber-reinforced concrete. In the next part, the authors’ own research and results of testing fiber-reinforced concrete with wires after pre-cleaning are shown. Chapter five summarizes the results of research and juxtaposes the most important observations that can be used for the practical use of fibers obtained in a simple recycling technology. The utilitarian value of the work is to show the practical possibilities of recovery (recycling) of used tires, in particular for the fiber-reinforcement of concrete. Among other things, it was shown that the addition of steel fibers (contaminated with rubber) to approximately 1.3% reduces the shrinkage of concrete with these fibers by 7–10% compared to a fiber-free concrete matrix cured under the same conditions.

Materials doi: 10.3390/ma19153337

Authors: Baoliang Li Hongrui Shang Liying Shi Sahi Wail Shouhua Liu Yuanyang Chen Binbin Huo

To investigate the application potential of ultrafine composite powder (UCP) as a novel supplementary cementitious material to replace ground granulated blast-furnace slag (GBFS) in cement-based materials and its underlying mechanism, this study first compared the activity differences between UCP and GBFS and their effects on mortar workability. Subsequently, multiple characterization techniques including XRF, XRD, TG/DTG, FTIR, mapping, SEM-EDS, and BET were employed to systematically examine the morphology, composition, particle size distribution, and pore structure characteristics of the two powders. Results show that UCP exhibits slightly higher 3 d and 28 d strength activity indices than GBFS, but contributes less to strength progression between 3 and 28 days. In terms of chemical composition, UCP contains lower combined CaO + MgO + Al2O3 content but significantly higher C and Fe levels and alkalinity than GBFS. Phase and microstructural analyses further reveal that UCP is predominantly composed of GBFS, fly ash (FA), steel slag, limestone powder, gypsum, superplasticizer, and alkaline activator, and is characterized as a mesoporous material with pores arising from fragmented FA, unburned carbon residues, and grinding-induced cracks. Quantitatively, the BET specific surface area, Blaine specific surface area, and total pore volume of UCP are 2.47, 1.59, and 3.31 times those of GBFS, respectively. Therefore, the early-age activity advantage of UCP is mainly attributed to the filling effect, the additional nucleation sites provided by its larger specific surface area, and the chemical activation induced by alkali and gypsum.

Materials doi: 10.3390/ma19153336

Authors: Robyn Erika Smith Paramespri Naidoo Adewumi John Babafemi Guven Akdogan

This investigation evaluated the suitability of solar waste sand (SWS), derived from recycled photovoltaic panels, as a raw material in clinker production. Raw materials were prepared, analysed, and used to design reference and SWS raw mix kneaded balls. The balls were subjected to sintering tests with varying peak temperatures; the clinker mineralogy was analysed using X-ray diffraction (XRD). The SWS raw mix contained 13.14% SWS with 78.31% and 8.55% of limestone and clay, respectively. The SWS clinker had 55.64 ± 2.26% C3S, 18.67 ± 1.27% β-C2S, 1.57 ± 0.35% CaOf, and 3.70 ± 1.41% MgOf at 1350 °C, all within recommended ranges. Minor oxides, including Na2O, K2O, and MgO, reduced the required sintering temperature relative to the typical 1450 °C, as expected. The presence of an amorphous layer suggested the optimal temperature may be around 1350 °C. Furthermore, the high Na2O content in the SWS clinker is believed to have helped stabilise β-C2S. Low C4AF and the absence of C3A might indicate its suitability as a clinker for sulfate-resistant cements. Incorporating SWS directly into the raw mix for clinker production is an innovative approach to both diverting solar waste from landfills and partially supplementing sand and limestone.

Materials doi: 10.3390/ma19153335

Authors: Gang Li Naijun Zhao Jiangang Li Xin Ma Shipeng Liu Guoxuan Zhang Shiren La Yang Shi Qiyuan Jiao

Conventional low-frequency antennas face a trade-off between miniaturization and radiation efficiency due to wavelength limitations. Although magnetoelectric (ME) antennas can overcome the electrical size constraint, existing designs lack structural tunability and performance enhancement. This paper proposes a Bézier curve-based (BCB) ME antenna that features a variable cross-section, introducing a shape tuning factor for precise geometric configuration. Using the lumped-mass method, the functional relationship between resonant frequency and the shape tuning factor is derived, establishing the theoretical basis for frequency tuning. A nonlinear multi-field coupled numerical simulation model is established for performance prediction. The BCB structure modifies internal stress distribution, enabling spatial reconstruction of magnetization modulation. The proposed design is validated by comparing the analytical model with our simulation results and literature-reported experimental data. Results show that the BCB design reduces resonant frequency and enhances converse ME (CME) coupling and far-field radiation without increasing material volume. Under clamped and free boundary conditions, the minimum resonant frequencies reach 7.2 kHz and 11.1 kHz, respectively, with CME coupling improved by 124% and 140%. When the shape tuning factor proposed in this work is set to 1/2, the proposed design degenerates into a traditional antenna with uniform cross-sections, which verifies the consistency of the established model.

Materials doi: 10.3390/ma19153332

Authors: Chengwei Ge Chunling Wu Zhen Zhang Kaile Cao Li Wang Mingwei Gao Xiangming He

Accurate state-of-health estimation of lithium-ion batteries under high-temperature conditions (40–50 °C) remains challenging because of accelerated electrochemical degradation and strongly nonlinear aging patterns. This paper presents a hybrid Ridge regression–convolutional bidirectional long short-term memory framework with a dual-level transfer learning strategy. A Ridge regression baseline first captures the global degradation trend, after which a convolutional bidirectional long short-term memory network learns the nonlinear residuals. For cross-battery adaptation, Ridge coefficients are transferred through prior-regularized regression, and the pre-trained network is fine-tuned using limited target-domain data. The method is validated on cycling datasets from three institutions, namely Tsinghua University, the University of Oxford, and Tongji University, covering 15 batteries under temperatures up to 50 °C. Four health-related features are extracted and adaptively denoised using locally weighted scatterplot smoothing. In single-battery extrapolation, the proposed method achieves a root mean square error as low as 0.0009 on cell B6 at 50 °C, outperforming random forest, long short-term memory, bidirectional long short-term memory, and Ridge regression by 91.1%, 88.6%, 87.7%, and 82.0%, respectively. A cross-battery ablation experiment showed that the dual-level transfer learning strategy reduced the root mean square error from approximately 0.009 to 0.0028, whereas increasing network complexity alone yielded only marginal improvement. A further hierarchical ablation showed that jointly adapting the Ridge prior and the residual network achieved a mean RMSE of 0.004325, representing reductions of 9.39%, 4.14%, and 6.92% relative to the no-adaptation, Ridge-only adaptation, and residual-network-only adaptation configurations, respectively.

Materials doi: 10.3390/ma19153334

Authors: Jiayu Guo Tao Xia Dingbo Cao Xue Liu Wei Zhang Yong Liu Jingchuan Zhu

Grinding is the final precision machining step for bearing rings, which induces subsurface gradients in microstructure and mechanical properties. Rolling contact fatigue life and service reliability are directly determined by the gradients. Current research of the grinding metamorphic layer in bearing steels is synthesized in this review. The formation mechanisms, characterization approaches, and the influence of grinding parameters on metamorphic layers is covered. The coupled thermal–mechanical–phase transformation framework encompasses heat-driven phase transformation, high-strain-rate gradient plastic deformation, and their interactions, which collectively govern the formation of the three-layer gradient structure. When the surface temperature exceeds the austenitization threshold, the governing regime shifts from mechanically dominated to thermally dominated, producing an abrupt increase in white layer thickness and concurrent dark layer softening. The capabilities and limitations of characterization techniques for probing the gradient microstructure and residual stress profile are evaluated. The influence of grinding depth, wheel speed, feed rate, wheel characteristics, and cooling conditions on the metamorphic layer is analyzed. The areas requiring deeper investigation are identified. These insights aim to establish correlations between the grinding process and the surface integrity and service performance of bearing components, and to provide directions for future research on the grinding metamorphic layer.

Materials doi: 10.3390/ma19153333

Authors: Matej Matuš Tomáš Vincze Michal Hanic Lubica Stuchlikova Martin Weis

Organic thin-film transistors based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) are attractive for low-cost, large-area electronics, but in unencapsulated devices, atmospheric oxidation generates charge traps whose electronic character—which product traps holes and which traps electrons—has not been mapped systematically. Here, 39 oxygen- and hydroxyl-related defect identities of DNTT are screened with the semi-empirical GFN2-xTB method, complemented by an a priori frontier reactivity index, and classified by the sign of the frontier-level shift. This sign obeys a simple rule: a net π-donating hydroxyl raises the HOMO and yields a hole trap, whereas a net π-accepting carbonyl or quinone lowers the frontier levels and yields a deep electron trap. Hybrid density-functional theory (B3LYP/def2-TZVP) confirms the sign rule and the ordering of the shifts across all closed-shell defect classes. The rule provides a compact, defect-level rationalisation of the well-known asymmetry whereby p-type acenes tolerate air far better than n-type ones. Finally, a hole trap of about 0.255 eV, measured by deep-level transient Fourier spectroscopy, is shown to be consistent with a hydroxyl-related origin, without claiming a unique microscopic assignment.

Materials doi: 10.3390/ma19153331

Authors: Dominik Logoń

Acoustic emission (AE) measurements are commonly used in studies of cementitious composites subjected to various types of loading. Recording macrocracks that result in a decrease in stress is not relatively difficult. This paper focuses on the possibility of identifying micro-events and microcracks during the compression of concrete with dispersed reinforcement. Most AE studies on cement composites correspond to a reduction in stress exceeding the elastic range defined by Hooke’s law, typically associated with the formation of the first crack and detected in the medium- and high-frequency ranges. However, identifying micro-events which do not reduce stress beyond the elastic range is difficult. This study demonstrates that such micro-events can be detected using low-frequency sound and infrasound. In many papers, medium- and high-frequency acoustic signals are effective for recording macrocracks or reinforcement damage. In this work, a 3D acoustic spectrum was used to analyze recorded data in the infrasound range in a concrete compressive test. This approach proved to be the most effective method for determining the critical point fcr (the end of the elastic range) regarding low-intensity micro-events and microcracks. This type of micro-damage has no significant influence on the linear stress–strain correlation at fcr. The results indicate that identifying micro-events and low-intensity microcracks using medium- and high-frequency acoustic signals is not possible and that infrasound should be considered for the detection. Significant differences in stress and displacement corresponding to fcr and fmax were confirmed in concrete compressive tests. The results indicate that accurately determining fcr is required for correctly assessing the durability of cementitious composites.

Materials doi: 10.3390/ma19153330

Authors: Safi Alsafi Siti Aminah Osman Faesal Alatshan Abdullah Alghossoon Azrul A. Mutalib

Concrete-filled steel tube (CFST) structures are widely used in modern infrastructure due to their superior strength, ductility, and composite action. However, long-term corrosion of the steel tube, particularly under aggressive environmental conditions, poses significant challenges to their durability and structural performance. This study presents a comprehensive review of corrosion mechanisms and mitigation strategies for CFST structures. The primary corrosion processes, including general corrosion, localized (pitting) corrosion, and circumferential corrosion, are critically examined with emphasis on the influence of chloride ingress, carbonation, marine exposure, and combined environmental actions such as freeze–thaw cycles and sustained loading. The effects of corrosion on structural behavior are analyzed in terms of load-carrying capacity, ductility, buckling resistance, and failure modes. A systematic evaluation of existing mitigation strategies is conducted, encompassing material-based approaches, protective coatings, cathodic protection systems, and structural strengthening techniques such as fiber-reinforced polymer (FRP), fabric-reinforced cementitious matrix (FRCM), and steel jacketing. The comparative performance of these methods is assessed based on effectiveness, cost–benefit considerations, service life extension, and practical implement ability. The review highlights that no single mitigation strategy is universally optimal; instead, integrated approaches combining multiple techniques provide the most effective long-term protection. Key research gaps are identified in the areas of long-term performance monitoring, internal corrosion detection, and durability modeling under combined environmental actions. The findings of this study provide valuable insights for the design, maintenance, and rehabilitation of CFST structures, contributing to the development of more durable and sustainable infrastructure systems.

Materials doi: 10.3390/ma19153329

Authors: Shuqi Li Yukun Zhou Xiaoyi Du Bing Hui

Asphalt pavements at high-altitude airports endure prolonged extreme low temperatures and large diurnal swings, imposing stringent demands on crack sealants, whose multi-scale adhesion failure mechanism remains unclear. Three SBS and crumb-rubber-composite-modified sealants, designated A, B and C, were characterized through surface free energy tests, pull-off and shear tests, fluorescence microscopy, FTIR and molecular dynamics simulations. Cross-scale correlation analysis and CRITIC-TOPSIS were applied to link and rank the sealants across scales. Work of cohesion, work of adhesion, pull-off strength and shear strength all rose monotonically with modifier content, and sealant C exhibited a 38.5% higher work of cohesion and a 52.4% lower CVφ than sealant A. Molecular dynamics simulations showed that electrostatic forces drove sealant–aggregate adhesion while van der Waals forces governed sealant–asphalt adhesion, with a simulation–experiment deviation of only 2.88–5.74%. A level-by-level transmission linked phase-morphology uniformity, intermolecular interaction, interfacial energy and macroscopic mechanical performance. Sealant C achieved a CRITIC-TOPSIS index of 1.000, far above 0.271 for B and 0.000 for A, and is recommended as the preferred material for crack sealing of high-altitude airport asphalt pavements.

Materials doi: 10.3390/ma19153327

Authors: Jiyang Wang Shuyu Lin Qiuyan Jiang Yu Peng Jingwen Shi Junxia Li Bo Zhang

Incorporating viscoelastic inclusions enhances the damping capacity of cementitious composites, but is often hindered by strength degradation and weak interfacial bonding. This study addresses this trade-off by investigating the synergistic modification of a cement matrix using carboxylated styrene-butadiene rubber latex (XSBRL) and chlorinated rubber (CR) powder, focusing on the age-dependent evolution of their joint energy-dissipation mechanisms. Macroscopic mechanical and microscopic test results reveal a pronounced synergy between latex and rubber powder, governed by possible interfacial interaction. The XSBRL film formed during hydration improves the compatibility between chlorinated rubber and the cement matrix, while its active groups further strengthen the bonding with hydration products. This interfacial coupling transforms the conventionally brittle transition zone into a ductile, high-friction network that maximizes dynamic stress transfer. Moreover, the temporal evolution of damping is governed by the competitive kinetics between cement hydration and polymer-film coalescence, shifting from early-age restructuring (7 to 14 days) to late-stage stabilization (28 days). To balance mechanical and dynamic properties, a recommended formulation of 10% XSBRL and 10% chlorinated rubber is established. This work provides a reference for clarifying the structure–property relationship of high-damping cementitious composites and for optimizing their mix designs.

Materials doi: 10.3390/ma19153328

Authors: Binghao Wang Yong Xu Yingda Zhang Ziqiang Lyu Zhen Wang Meiling Gu

This study systematically investigates the effects of water-to-binder ratio, total binder content, silica fume content, and fly ash content on the fluidity and compressive strength of Type IV cement-based grouting materials. An L16(44) orthogonal experimental design was adopted to evaluate the influence of these four factors on initial and 30 min slump flow, as well as 1-day, 3-day, and 28-day compressive strength. The range analysis results indicate that silica fume content exerts the most significant effect on initial slump flow, while the water-to-binder ratio predominantly governs the 30 min slump flow and early-age compressive strength, such as at 1 day and 3 days. The total binder content is identified as the key factor influencing the 28-day compressive strength. Furthermore, supplementary tests on the combined incorporation of fly ash and silica fume reveal that silica fume enhances early-age strength but reduces fluidity, whereas fly ash improves fluidity but promotes later-age strength development, with an optimal substitution range for both admixtures. Microstructural analyses including XRD and SEM and hydration heat tests further elucidate the underlying mechanisms, demonstrating that the effects of the two admixtures optimize the hydration process and microstructure densification. Based on the comprehensive evaluation, the optimal mix proportion was determined as A3B2C4D2, corresponding to a water-to-binder ratio of 0.31, a fly ash content of 15%, a total binder content of 690 kg/m3, and a silica fume content of 8.5%. This optimized formulation achieves a balanced performance in both workability and strength development.

Materials doi: 10.3390/ma19153326

Authors: Wenxue Wang Lu Guo Yuan Fang Haolin Gong Yang Li Kun Zhang Jian Chang Jiawei Liu Shuli Zhao

Cement–sodium silicate binary grout is widely used for water sealing and stratum reinforcement in deep underground engineering. Curing pressure profoundly affects the mechanical performance and microstructure of the hardened grout, whereas its pressure-dependent mechanical responses remain insufficiently understood. This study comprehensively investigates the grout’s workability, mechanical properties and water-loss degradation characteristics, combining scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) for microscopic analysis. The results show that the combined addition of 3% sodium bentonite and 1% polycarboxylate superplasticizer effectively mitigates slurry bleeding. An increased cement-sodium silicate volume ratio (C/S) improves fluidity and gel time, and C/S ratios of 0.4, 0.5 and 0.6 were adopted for mechanical tests. Under ambient conditions, grout compressive strength increases with curing age but declines at higher C/S ratios. Curing pressure presents a non-monotonic influence on strength: the strength reaches a minimum at 1.0 MPa and partially recovers at 2.0 MPa, which may result from the competition between pore compaction and hydration gel network damage. Water-loss-induced strength degradation undergoes three typical stages. Grout with lower C/S ratios cured under higher pressure possesses better crack resistance and residual strength. This study clarifies the pressure-adapted mechanism of the grout, providing guidance for its optimal proportioning and application in high-pressure underground engineering.

Materials doi: 10.3390/ma19153325

Authors: Ming Lv Yongkang Fu Jinchao Yue Zikai Xu Shenyuan Wang Yangming Gao Chao Zhang

Improving the flame-retardant performance of asphalt is particularly important for tunnel pavements, where confined environments can intensify fire hazards and smoke accumulation. This study prepared different modified asphalt binders to investigate their flame-retardant performance and rheological properties. The limiting oxygen index and smoke density rating were first used to evaluate the flame-retardant and smoke-suppression performance. Frequency sweep tests were then conducted to analyze the rheological behavior, aging characteristics, and low-temperature cracking resistance of the binders. Finally, microscopic tests were performed to reveal the thermal decomposition behavior and modification mechanism. Results showed that the incorporation of FR02 increased the limiting oxygen index of the warm-mix modified binders by more than 47%. Among the investigated binders, 13% fast-melting warm-mix flame-retardant composite modifier (SBS-WZ) exhibited the highest limiting oxygen index of 30.95% and the lowest smoke density rating of 57.73, indicating the best experimentally measured flame-retardant and smoke-suppression performance. At a reduced frequency of approximately 10−2 rad/s, the unaged 13%SBS-WZ binder exhibited a complex modulus of approximately 2.0 × 105 Pa, nearly one order of magnitude higher than those of the conventional 4%SBS- and 4%fast-melting SBS modifier (SBS-T), while its phase angle was approximately 6–10° lower. At −24 °C, the creep stiffness and creep rate of the unaged 13%SBS-WZ binder were approximately 654 MPa and 0.246, respectively. After Pressure Aging Vessel (PAV) ageing, these values changed to approximately 720 MPa and 0.237. Moreover, the onset decomposition temperature of 13%SBS-WZ was 392.1 °C, which was 17.2 °C higher than that of 4%SBS-T. Together with its higher residual mass, this result suggests enhanced thermal stability and residue-forming potential, which may partly explain the measured improvements in flame-retardant and smoke-suppression performance. However, the increased complex modulus and reduced creep rate indicate a concurrent loss of low-temperature flexibility. The findings can provide theoretical guidance and technical support for the application of this material in tunnel asphalt pavements.

Materials doi: 10.3390/ma19153324

Authors: Anhua Xu Jiming Xiao Yuchang Duan Huaxin Chen Jincheng Yu Fayun Lei Dongliang Kuang

Numerous studies have investigated the application of iron tailings as raw materials for cement concrete, while rare efforts have been devoted to developing epoxy pavement repair mortars where graded IT function simultaneously as fine aggregate and filler. This study prepared epoxy resin mortar for rapid repair of cement concrete pavement using graded iron tailings (IT) as fine aggregate and filler. All mixtures employed IT as fine aggregate, where the mass proportion of IT filler relative to the total IT mixture varied from 0% to 40%. The effects of IT filler content on workability, curing temperature, mechanical properties, volume stability, and bond strength were investigated, accompanied by microstructural analysis. Experimental results reveal that the incorporation of IT filler ameliorates the fresh workability and shortens the setting time of epoxy mortar, whereas the compressive strength, flexural strength and interfacial bond strength exhibit an initial ascending followed by a descending trend with the increasing IT filler fraction. The optimal IT filler content is determined to be 20%. For fresh-state performance, the modified mortar delivers a flowability of 176.8 mm (+29.7% relative to EM-0) and a setting time of 127 min. In terms of hardened mechanical and bonding properties, the 28-day compressive strength, 28-day flexural strength and 7-day flexural bond strength reach 113.2 MPa (+17.2%), 42.5 MPa (+34.0%) and 9.1 MPa (+75.0%), respectively, in comparison with the reference specimen EM-0. Microscopic characterizations deliver indirect evidence that appropriate IT filler may refine internal pore-size distribution, densify matrix microstructure and suppress crack propagation. The failure mode changed from pure interfacial debonding to cohesive failure in the cement substrate. This work provides a green scheme for resource utilization of iron tailings in high-performance pavement repair materials.

Materials doi: 10.3390/ma19153323

Authors: Sarah Fahad Alsenani Sultan Binalrimal

Background: Ultra-fast high-irradiance curing shortens exposure time, but its effects on conversion and polymer-network integrity may vary among bulk-fill resin composites. This in vitro study was designed as a materials-level investigation of irradiated-surface polymerization behavior. It evaluated irradiated-surface degree of conversion and polymer-network quality while deliberately excluding assessment of depth of cure or polymerization throughout the 4 mm bulk increment. Methods: Eighty disk specimens (6 mm × 4 mm) of Filtek One Bulk Fill, SDR Plus, Beautifil Bulk Flowable, and Beautifil Bulk Restorative (n = 10/material/protocol) were cured with a polywave LED at 1200 mW/cm2 for 10 s or 3000 mW/cm2 for 3 s. Degree of conversion (DC) was measured by ATR-FTIR on the irradiated (top) surface only. Ethanol-induced softening (ES%, Knoop-hardness reduction at the irradiated surface after 24 h ethanol immersion) served as an inverse, indirect indicator of polymer-network quality (cross-link density). Data were analyzed by two-way ANOVA and Tukey tests (α = 0.05); the DC–ES% relationship was examined by Pearson correlation at the individual-specimen level (n = 80). Results: Ultra-fast curing yielded higher pooled DC (66.30 ± 10.06%) than conventional curing (59.37 ± 7.96%; p < 0.001), but the effect was material-dependent: DC increased significantly for Filtek One Bulk Fill (p < 0.001) and Beautifil Bulk Flowable (p = 0.035), but not for SDR Plus or Beautifil Bulk Restorative. ES% was influenced mainly by material (p < 0.001) and less by curing protocol (p = 0.009). At the specimen level (n = 80), DC and ES% showed a weak but statistically significant negative correlation (r = −0.31, p = 0.006). Conclusions: Within the conditions of this study, irradiated-surface polymerization behavior under ultra-fast curing depended primarily on composite formulation, underscoring the need to evaluate both conversion efficiency and polymer-network quality when optimizing dental restorative materials. Because conversion was assessed only at the irradiated surface, these findings describe irradiated-surface behavior and do not provide evidence of adequate cure at the bottom of the 4 mm increment.

Materials doi: 10.3390/ma19153322

Authors: Balasubramanian Ramesh Essmat Showman S. A. Muhammed Abraar Kuldeep Kumar Saxena Mohammed Y. Tharwan Naif Alsaadi Sharaf Al Sofyani Ammar H. Elsheikh

The journal retracts the article titled, “Microstructure, Mechanical Characteristics, and Wear Performance of Spark Plasma Sintered TiB2–Si3N4 as Affected by B4N Doping” [...]

Materials doi: 10.3390/ma19153321

Authors: Ruijie Xie Wenhu Zhang Jun Xu Jianbo Xu Yiping Xu

While the beneficial effect of residual compressive stress (RCS) on rolling bearing fatigue life is empirically well-established, the underlying mechanisms, particularly its influence on the subsurface stress field responsible for fatigue initiation, remain inadequately explored. This study employs a sophisticated finite element (FE) model of a ball–raceway contact, which incorporates a depth-dependent gradient of RCS, to elucidate the underlying mechanisms. The results demonstrate that RCS not only reduces the contact stress at the interface but also fundamentally alters the subsurface stress field by shifting the location of the maximum shear stress to a greater depth and reducing its inclination angle. These changes collectively delay crack initiation and propagation, explaining the observed enhancement in fatigue life. Furthermore, the study demonstrates that the beneficial effect of RCS is depth-dependent and persists significantly even under high-friction conditions.

Materials doi: 10.3390/ma19153320

Authors: Calogero Volpe Leonardo Pagnotta

This second part extends the system-level framework established in Part I by examining advanced adhesive and sealant technologies through a performance-, circularity-, and application-oriented perspective relevant to contemporary packaging systems. While Part I focused on material classification, bonding and sealing mechanisms, regulatory aspects, and interfacial design principles, the present review analyses how advanced adhesive and sealant systems behave under realistic converting, sealing, service, recycling, and end-of-life conditions. Particular attention is devoted to bio-based and compostable adhesives, recyclable mono-material architectures, advanced multilayer sealants, debond-on-demand systems, and smart or reversible interfaces designed to support circular packaging strategies. The review critically discusses the principal adhesive and sealant performance metrics—including bond strength, seal strength, seal initiation temperature (SIT), hot-tack behaviour, cohesive durability, processing robustness, and hydrothermal resistance—in relation to packaging reliability, barrier preservation, processability, and compatibility with industrial converting operations. The analysis additionally addresses interfacial failure mechanisms, recyclability constraints associated with multilayer structures, food-contact compliance, migration and non-intentionally added substances (NIAS), and the growing role of design-for-disassembly and circularity-oriented interfacial engineering. Emerging transition strategies involving waterborne systems, low-migration formulations, recyclable sealants, dynamic covalent networks, and controlled debonding technologies are evaluated in terms of their potential to reconcile packaging performance with sustainable material management. By integrating material-specific developments with system-level packaging considerations, this review highlights how adhesive and sealant interfaces increasingly represent critical design variables governing the balance between mechanical performance, sealing reliability, processability, recyclability, compostability, and circularity in next-generation packaging systems.

Materials doi: 10.3390/ma19153319

Authors: Hongyang Xin Changfeng Dong Jianjun Mao Tao Peng Wei Zhang Zhien Ning Xiaoyong Wu

We investigated the impact of Au ion irradiation on the corrosion behavior of medium-entropy alloy coatings (MEAs), with and without Al addition, in simulated primary water of pressurized water reactors (PWRs). The results indicated the formation of double-layer oxide films on the surfaces of both types of coatings, consisting of outer oxide particles and a protective inner oxide layer. The high-fluence irradiation modified the microstructures of both coatings and accelerated their corrosion kinetics. However, the coating with a slight addition of Al demonstrated superior post-irradiation corrosion resistance owing to its enhanced lattice distortion effect within the system, inhibited atomic diffusion, and reduced impact of irradiation on its phase structure. A comprehensive discussion was carried out on the corrosion processes of the coatings, both irradiated and non-irradiated.

Materials doi: 10.3390/ma19153318

Authors: Yunhan Zhao Xueting Wang Jinyang Chen

In this study, hectorite intercalated with octadecyl trimethylammonium ions was synthesized via one-pot synthesis, and the octadecyl trimethylammonium-modified hectorite was used as an adsorbent to remove phenol from an aqueous solution. The pH and content of the adsorbent were studied to determine the optimized conditions for the adsorption of phenol. The phenol removal rate attained for 50 mL of 100 mg/L initial phenol solution at pH 12 was about 92.3% when 0.5 g of adsorbent was used. As for the adsorption isotherm, the Langmuir and Freundlich models were appropriate. The adsorption kinetics were in accordance with the pseudo-second-order model, and the activation energy (Ea) was about 11.15 kJ/mol. The modified hectorite could be recycled and reused, maintaining a high adsorption amount after five cycles.

Materials doi: 10.3390/ma19153317

Authors: Jakub Wręczycki Katsiaryna Nauharodskaya Dariusz M. Bieliński Grzegorz Mlostoń

Utilization of tetra-n-butylammonium fluoride (TBAF) as a new, hitherto unknown devulcanization aid in the chemical devulcanization of sulfur crosslinked diene rubber has been demonstrated. The influences of crosslink structure (the ratio of mono-, di-, and polysulfidic bonds) and carbon black (CB) loading on the efficiency of acrylonitrile-butadiene-rubber (NBR) devulcanization have been studied. The rubber vulcanizates were treated with TBAF solutions under varying conditions (solution concentration, solvent type, temperature, and reaction time). Changes in crosslink density and other relevant network properties of the rubber vulcanizates were measured. Results showed a significant reduction in crosslink density—up to 50% after chemical treatment. The fluoride-based approach, in which fluoride salt is a source of nucleophilic fluoride anions (F−), can cleave the sulfidic crosslinks, demonstrating significant potential for efficient recycling of used rubber vulcanizates by their devulcanization.

Materials doi: 10.3390/ma19153316

Authors: Szymon Swierczyna

This paper presents the results of experimental investigations of the flexural capacity of the main beams in a storage platform with plan dimensions of 5.0 m × 2.0 m. The platform was designed as a grid structure, with main beams made of cold-formed channel sections and crossbeams made of sigma-section members. The crossbeams, spaced at 0.6 m, were connected to the main beams using M12 bolts and angle cleats. Eight test specimens were examined, with section heights ranging from 250 to 500 mm and wall thicknesses of 3 or 4 mm, fabricated from S350GD+Z steel. Loading was applied in a four-point bending scheme until failure of one of the main beams, while recording the moment–deflection relationship. The obtained failure loads were compared with the design resistances calculated in accordance with EN 1993-1-3. Additionally, GMNIA analyses were performed for the tested storage-platform structures using the Idea StatiCa Member version 24.1 software, incorporating measured material properties and equivalent geometric imperfections in accordance with prEN 1993-1-14. The adopted procedure included a sensitivity study to investigate the influence of different combinations of local and distortional buckling mode imperfections on the numerical results. The observed behaviour was characterized by interaction between distortional and local buckling modes, accompanied by yielding in the compression zone. The GMNIA analyses predicted the ultimate bending resistance with good accuracy, yielding FEM-to-test resistance ratios between 0.93 and 0.98. The sensitivity study indicated that the predicted ultimate resistance was only weakly affected by the assumed combination of local and distortional imperfection modes. For the investigated platform systems, the effective section approach according to Eurocode 3 provided accurate predictions of the ultimate resistance, with calculated-to-test resistance ratios ranging from 0.96 to 1.01. This agreement is discussed in the context of the possible stiffening effect of crossbeam-to-web connections.

Materials doi: 10.3390/ma19153315

Authors: Kiril Dimitrov Imasha Danwatte Vesela Stoycheva Leonid M. Goldenberg Daniel Pinkal Michael Wegener Christian Dreyer Michael Herzog

The objective of this study was to identify chitosan formulations suitable for sustainable functional integration into composite materials. To this end, the influence of solvent type (acetic acid and lactic acid) and chitosan molecular weight on film formation, rheological behavior, thermal response, thermo-optical properties, chemical structure, and piezoelectric performance was systematically investigated. Optimized casting and drying procedures produced transparent, homogeneous, and mechanically stable films suitable for comprehensive characterization. Rheological and thermo-optical analyses demonstrated that solvent selection strongly influenced polymer network formation and molecular mobility. Films prepared using acetic acid exhibited denser and stiffer polymer networks with improved dimensional stability, whereas lactic acid produced more flexible and elastic films. Thermogravimetric analysis revealed only minor differences in the intrinsic thermal stability of the investigated films, while FTIR confirmed that the solvent systems did not alter the chemical structure of chitosan. Electrical measurements carried out whilst the system was subjected to periodic mechanical excitation revealed weak but equally periodic electrical signals, which demonstrate a sensor functionality. These results demonstrate that chitosan films possess tunable structural, thermal, and potential mechanoelectrical sensor properties and highlight their potential as sustainable, functionally integrated components in composite material systems.

Materials doi: 10.3390/ma19153314

Authors: Chen Chen Yichao Zhu Zhiping He Yanfei Wang Weifeng Xu Chenyang Qiu Zhennan Liu

The corrosion behavior of symmetric (S-joint) and asymmetric (A-joint) double-sided friction stir-welded (DS-FSW) 7A65 aluminum alloy thick plates was investigated in 3.5 wt% NaCl solution. The S-joint, produced using the same large tool (Φ30 mm) for both passes, imposes two high-heat thermal cycles that result in insufficiently fragmented intermetallic particles (IMPs), coarse grains, and severely overaged heat-affected zones (HAZs). In contrast, the A-joint, employing a smaller tool (Φ24 mm) for the second pass, reduces the total heat input and achieves a refined microstructure with fine (2–3 µm), rounded IMPs in the second-pass weld nugget (WNZ-S) and less degraded HAZs. Electrochemical measurements reveal that the HAZ-Overlap (HAZ-O) is the most anodic zone in both joints. The S-joint shows a larger potential spread (up to ~120 mV) and higher corrosion current density than the A-joint. The hierarchical galvanic coupling, where macro-galvanic corrosion between the anodic HAZ-O and cathodic WNZs drives severe localized attack, while micro-galvanic corrosion around coarse IMPs initiates trenching, is elucidated. The A-joint mitigates this damage due to its reduced galvanic driving force (smaller potential spread of ~74 mV) and improved microstructural homogeneity. The enhanced corrosion resistance of the A-joint is attributed to grain refinement, effective IMP fragmentation, and a less degraded HAZ microstructure.

Materials doi: 10.3390/ma19153313

Authors: Pengzhai Li Kangzhen Sun Yi Wu Qiuli Fang Yin Zhang

To address the dependence on organic solvents, costly silicon precursors, and complex processing in conventional silica aerogel preparation, this study developed a green and low-cost aqueous route using water glass as the silicon source. The sol–gel process was optimized through an orthogonal experimental design by regulating precursor concentration, pH, temperature, and catalyst dosage, enabling the formation of a stable three-dimensional silica network. Under the optimized conditions, the unmodified silica aerogel exhibited low density, high porosity, and a typical mesoporous structure, with a specific surface area of 707.87 m2/g, an average pore size of 5.75 nm, and a thermal conductivity of 0.0408 W/(m·K). After HMDS vapor-phase modification, hydrophobic methyl groups were introduced onto the aerogel surface, increasing the water contact angle to 132.3°. Among the modified samples, S3 showed the lowest thermal conductivity of 0.0360 W/(m·K), indicating good thermal insulation performance. This work provides a feasible strategy for preparing hydrophobic silica aerogels through a cost-effective aqueous process, showing potential for greener and large-scale production of silica aerogel materials.

Materials doi: 10.3390/ma19153311

Authors: Delia Niculina Piscoiu Simona Rada Tudor Panfil Toader Horatiu Vermesan

In recent years, alternative recycling approaches such as melt quenching and electrochemical evaluation methods have been investigated to assess the quality and performance of recovered lead materials. In this study, several samples obtained from the recycling process were analyzed electrochemically. The objective was to compare their electrochemical parameters and identify the samples with better electrochemical performance. The main methods used in this paper are X-ray diffraction analysis and voltammetric investigations using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). Electrochemical characterization provides valuable information about the behavior of recycled lead materials. Parameters such as half-wave potential (E1/2), anodic current density (Ia), and solution or bulk resistance (Rb) are commonly used to evaluate electrochemical activity and conductivity. The electrochemical analysis reveals noticeable differences among the samples studied. The analysis of CV, LSV, and EIS indicates that the samples P2 (doped with CuO and Sb2O3) and P3N (doped with CaO/Fe2O3/Fe) exhibit the most favorable electrochemical behavior for lead acid battery applications, with the highest current response and smallest peak separation, suggesting efficient Pb/PbSO4 redox reactions and minimal polarization.

Materials doi: 10.3390/ma19153312

Authors: Wenxia Zhang Yangjun Wang

In conventional CNC machining, the workpiece clamping pose is registered with a preset CAD model under multiple geometric constraints to establish the machining reference frame. The tool path, generated from this model, is subsequently used to produce components of identical geometry. However, this paradigm proves inadequate when a final shape must accommodate morphological variations specific to each individual blank. Manual grinding, as an alternative, is not only inefficient and hazardous but also relies heavily on subjective quality assessment. To address these challenges, we propose an adaptive local-region milling strategy tailored for blanks with similar yet non-identical surface morphologies, enabling the finished geometry to adjust dynamically to each workpiece. Under conditions of under-constrained clamping, visual positioning is first employed to automatically locate the target regions. Line laser scanning is then conducted over the planned area to acquire high-density point clouds. Through segmentation, points lying outside the region to be machined are extracted, from which a theoretical post-machining surface is reconstructed. Milling toolpaths are subsequently planned based on this reconstructed model to compensate for surface variations across different blanks. Experimental validation on a three-axis CNC milling machine demonstrates that the proposed adaptive strategy effectively replaces manual grinding by removing the bulk of the machining allowance from locally variant surfaces. With the reconstructed model serving as the reference, 77.1 percent of the machining errors fall below 0.055 mm. These results confirm that the method yields a smooth and level surface finish, thereby meeting the fundamental requirements for such adaptive machining tasks.

Materials doi: 10.3390/ma19153310

Authors: Yunqing Xia Shaomu Wen Hongfa Huang Yanli Luo Xu Han Lifen Tong Jingyu Hou Hongjie Li

A series of self-toughening benzoxazine resins containing amino-terminated polyarylene ether nitrile (APEN) segments were synthesized from bisphenol-A, paraformaldehyde, and a mixed amine source of APEN and melamine. Unlike conventional physical blending toughening, the APEN segments are covalently incorporated into the benzoxazine network via their amino end groups. This chemical integration not only significantly improves toughness but also simultaneously enhances thermal and dielectric properties, overcoming the common trade-off of “toughening without heat resistance”. Meanwhile, melamine serves as one of the amine sources; its excess amino groups can catalyze the ring-opening polymerization of benzoxazine, which helps to reduce the curing temperature. The effects of APEN content and curing temperature on the properties of the resin and glass fiber composites were studied. The incorporation of APEN optimized the crosslinked network, balancing rigid aromatic structures with flexible ether linkages. As the proportion of APEN segments increased, the thermal decomposition thresholds and char residue were notably enhanced, signifying progressively improved thermal resistance. For composite systems cured at 220 °C, flexural strength exhibited a continuous upward trend with rising APEN content, while the flexural modulus remained steadily within a range of 23–25 GPa, and the impact strength was remarkably elevated from 45 kJ/m2 to values spanning 60–73 kJ/m2. A further curing treatment conducted at 300 °C facilitated additional crosslinking of nitrile moieties, yielding a further enhancement in flexural strength, particularly at lower APEN contents. Fracture surface analysis confirmed the toughening effect, evidenced by the transition from smooth brittle fracture to dendritic crack patterns. In addition, the composite achieved its lowest dielectric constant of 4.2 at an APEN loading of 20 wt.% when cured at 300 °C. Overall, this investigation presented a viable and effective strategy for the design and fabrication of high-performance, self-toughened benzoxazine-based composites.

Materials doi: 10.3390/ma19153309

Authors: Guangchao Guo Jiangshan Zhang Mengjing Zhao Shufeng Yang Xiaotan Zuo Qing Liu

In the continuous casting process, the flow velocity of molten steel at the surface of the mold directly influences the melting of the flux, slag entrainment behavior, and the uniformity of heat transfer. Fast and accurate prediction of the magnitude and distribution of surface-flow velocity is crucial for defect suppression and ensuring continuous casting quality. In this study, a three-dimensional electromagnetic–fluid dynamic coupled model was established and validated to simulate the molten steel flow behavior under various casting speeds, Electromagnetic Stirring (EMS) currents, EMS frequencies, and Submerged Entry Nozzle (SEN) immersion depth. Subsequently, the maximum surface velocity in the mold was fitted to derive a predictive formula under different conditions; the median range and width of the surface high-velocity range were predicted in a similar way. As a result, a regression model derived from Computational Fluid Dynamics (CFD) was built to predict the maximum mold surface velocity and the high-velocity range within milliseconds. The reliability of the regression model was verified by newly generated simulation results, with the relative error between the predicted and simulated maximum surface velocities kept within 2%. It was shown that the maximum surface velocity increases with casting speed and EMS current but decreases with EMS frequency. The median range of the high-velocity range decreases with increasing casting speed and current. The immersion depth of SEN had a minimal impact on the maximum surface velocity in the mold and the high-velocity range. This regression model is beneficial for rapid mold design and for predicting potential slag entrainment, breakout risks, and billet defects, for the purpose of intelligent continuous casting.

Materials doi: 10.3390/ma19153308

Authors: Ce Feng Yuting Zhang Xiao Zhang Shikai Chang Fuhao Zhang Linyuan Cao Jingya Dong Rongdong Wang

Sodium hydride (NaH) is the main by-product generated during the operation of the cold traps in a sodium-cooled fast reactor. Its thermal decomposition releases hydrogen gas, posing a safety hazard. However, understanding the atomic-scale decomposition mechanism remains challenging because conventional simulation methods are limited in the accessible length and time scales. This study developed a deep neural network potential (DP) for the NaH system using the DP-GEN active learning framework. Benchmark tests show that the DP model accurately reproduces density functional theory (DFT) reference energies, forces, equations of state, elastic properties, and phonon spectra. In particular, the DP-predicted bulk modulus and lattice constant are in good agreement with DFT results and close to experimental values, significantly outperforming the empirical ReaxFF potential. Subsequently, we conducted large-scale Deep Potential Molecular Dynamics (DPMD) simulations to investigate the thermal decomposition behavior of NaH clusters and a slab model. The simulation results reveal model-dependent thermal responses of NaH. In the original Na48H48 cluster simulation heated from 100 to 1200 K, a structural transition and disordering were observed, but no H2 formation occurred within the simulation time. In contrast, the slab model heated from 300 to 1500 K exhibited surface disordering, Na-H bond cleavage, H-H bond formation, cluster detachment, and H2 formation and release at elevated temperatures. A supplementary higher-temperature Na48H48 cluster simulation further showed cluster dissociation in the 1000–1500 K range. These results provide atomistic insight into the model- and temperature-dependent decomposition behavior of NaH and suggest that the DP model is a useful tool for studying hydrogen-related processes in alkali metal hydrides.

Materials doi: 10.3390/ma19153307

Authors: Hamza El Fahime Mohammed Radouani Benaissa El Fahime

High-volume injection molding systems for plastic part production operate under severe thermo-mechanical loading repeated at high production rates. Therefore, premature breakage of hot-work tool steel core inserts directly interrupts production continuity and creates a recurrent maintenance problem. To address this failure mode, this study collected production inputs and failure evidence and established a reliable interpretation by linking computer-aided engineering simulations of the plastic injection molding process, structural FEA of the insert response, and cumulative fatigue assessment using a TMF-creep damage model. This integrated approach provides a comprehensive framework for failure root-cause identification and service-life prediction and improving insert durability in mass-manufacturing environments.

Materials doi: 10.3390/ma19153306

Authors: Wuqing Lin Hongyang Li Zhongwei Hu Fuxin Peng Zhihao Zhou Yiqing Yu Yueqin Wu Xipeng Xu

4H-SiC substrate is widely employed in semiconductor device fabrication owing to its unique crystal structure and excellent physicochemical properties. However, its deformation behavior during substrate processing remains complex and not fully understood. In this study, molecular dynamics (MD) simulations were performed to systematically investigate the deformation mechanism of single-crystal 4H-SiC during nanoindentation, serving as an atomic-scale analogue of the workpiece–abrasive interaction during substrate processing. Specifically, the relationship between the fluctuations of the load–depth curve and slip were revealed, with particular emphasis on the basal slip (BS) and prismatic slip (PS) behaviors. The results indicate that the fluctuations in the load–depth curve are primarily associated with the nucleation and propagation of dislocations. The initiation of BS is predominantly influenced by the atomic arrangement and stress distribution, while PS initiates at the terminus of BS as the indentation depth increases. Finally, nanoindentation experiments were conducted to validate the reliability of the MD simulations. These findings provide valuable insights into the deformation mechanism and mechanical behavior of 4H-SiC during practical substrate processing.

Materials doi: 10.3390/ma19153305

Authors: Karsten Fleischer Priyanka Bhatnagar Ciarán Cooling Eva Gurley Dominik Jakobczak Ainur Zhussupbekova

Spray pyrolysis is a popular method for the low-cost synthesis of oxides and other compounds in thin-film form. Here, we discuss several nuances of using this method for ternary and quaternary compounds. Specifically, we outline how precursor solubility and thermal decomposition, as well as desorption of intermediate species from the sample surface govern the spray pyrolysis growth process. We demonstrate how the stoichiometry transfer from solution to film can be affected in selected test cases. We present real-time optical growth measurements of the behaviour of individual Cu, Cr, Zn, and Sn precursors, as well as post-growth analysis of film composition by X-ray photoelectron spectroscopy for ternary transparent conducting oxides (TCOs; p-type: CuxCrO2, SnTiOx; and n-type: a-ZnSnO3). We illustrate how several steps of spray pyrolysis affect the stoichiometry transfer from the solution to the ternary thin film. Using binary Cu2O as a test case, we also show how the choice of instrument geometry and nozzle type can affect film homogeneity. All materials discussed have been chosen to highlight potential difficulties of the spray pyrolysis process of ternary, quaternary, or even more complex oxides, and the mechanisms should be considered for other materials as well. We therefore also provide an extensive overview of suitable precursor salts with similar expected properties as used in this experimental work to guide future ternary oxide studies.

Materials doi: 10.3390/ma19153304

Authors: Kaimeng Wang Yingli Li Molin Su Hongqiao Yan Yue Zhao Lei Zhao

This study investigates the atomic-scale effects of hydrogen concentration and Ni content on crack propagation in Fe-Ni alloy models using molecular dynamics methods. A Mode I crack model with a (001)[100] orientation was constructed, and hydrogen atoms were locally introduced at the crack tip with concentrations of 5.3 at.% and 14.3 at.%. Fe-Ni alloy models with 5%, 10%, 15%, and 20% Ni were compared in terms of crack growth, dislocation evolution, stacking fault energy, and hydrogen diffusion. The results show that local hydrogen introduction has a limited effect on the peak stress–strain response, while hydrogen clearly accelerates crack propagation in the middle stage, especially at high concentrations. For the 10% Ni model, the middle-stage crack growth rate increases to 0.36 Å/ps under 14.3 at.% crack-tip hydrogen. Crack growth in all models shows three stages. The 15% Ni model exhibits a clear plateau in the second stage and the shortest final crack length. Further analysis shows that Ni content regulates dislocation behavior through stacking fault energy. At 15% Ni, sustained dislocation entanglement and high-density dislocation multiplication occur near the crack tip, which helps dissipate local stress. Hydrogen diffusion analysis indicates that hydrogen mobility is lower in the 15% Ni model, which may be related to hydrogen retention near dislocation-rich regions. A normalized comparison based on hydrogen diffusion and middle-stage crack growth rate further identifies 15% Ni as the lowest crack propagation tendency composition among the studied models. These results provide atomic-scale data for Ni-content optimization in hydrogen-resistant alloys, although the direct engineering transfer of the findings is limited by the length and time scales of molecular dynamics simulations.

Materials doi: 10.3390/ma19153301

Authors: Daren Peng Andrew S. M. Ang Nam Phan Michael R. Brindza Ben Main Rhys Jones

The paper is the first to highlight what appears to be a unique and unusual failure mechanism that is associated with cracks that nucleated from corrosion pits in aluminium alloy (AA) 7085-T7452 specimens that were tested under a variable amplitude load spectrum. In this study, cracks initially nucleated at corrosion pits and first grew as would be expected, namely at ninety degrees to the surface and perpendicular to the applied load. However, after reaching a depth of approximately 2 mm, these various Mode I cracks transformed into what can be best described as interlayer cracks with their surfaces at an angle of approximately ninety degrees to the initial fatigue crack surface. Analysis of the failures revealed that the maximum value of the stress intensity factor at which this phenomenon occurred, which we have defined as KIL, was substantially less than the fracture toughness for this material. As such, failure was not due to classical Mode I failure, but rather due to K exceeding what we will term KIL. Despite the unusual failures, it was found that, up to the point where this phenomenon occurred, the crack growth versus cycles histories could be reasonably accurately predicted using the small crack growth equation developed by the authors in a prior study on AA 7085-T7452 specimens with a fastener hole.

Materials doi: 10.3390/ma19153303

Authors: Bo Li Xiang Zhou Tao Chen Zhenhua Yang Mingyu Sha Lianwei Li Liangying Li

The utilization of industrial solid waste is crucial for sustainable development. This study developed a novel composite cementitious material (OSSC-GGBS) using oil shale semi-coke and slag as cement substitutes. A multi-objective optimization method was employed to determine the optimal formulation of OSSC-GGBS. Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM-EDS), Thermogravimetric Analysis (TG-DTG-DSC), and pH testing. Finally, the synergistic effects of oil shale semi-coke and slag on the mechanical properties of this composite material were thoroughly investigated. Results indicate that the composite cementitious material exhibits optimal performance when the mass ratio of oil shale semi-coke to slag is 3:7, cement content is 15%, water glass modulus is 1.4, and water glass content is 10%. Microscopic analysis revealed that the synergistic interaction between oil shale semi-coke and slag optimized the microstructure of OSSC-GGBS. Its hydration products primarily consisted of C-S-H gel, Ca(OH)2, and AFt, forming a dense and stable microstructure. Simultaneously, under alkali-activated conditions, oil shale semi-coke and slag synergistically participated in hydration reactions and secondary pozzolanic reactions. This significantly promoted the formation of cementitious products such as calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H). These products filled internal pores to form a network skeleton, thereby optimizing the microstructure.

Materials doi: 10.3390/ma19153302

Authors: Paulina Rozpędowska Małgorzata Wójcik Mateusz Golda Agnieszka Woszuk Lidia Bandura Szymon Malinowski Wojciech Franus

The increasing demand for sustainable bitumen modifiers has stimulated interest in bio-based materials capable of improving binder performance while reducing environmental impact. This study investigates the influence of corn starch on the thermo-oxidative aging kinetics of paving-grade bitumen. Unmodified 50/70 bitumen and binders containing 4, 6 and 8 wt.% corn starch were subjected to laboratory aging at 100 °C and 140 °C for up to 120 h. The aging process was evaluated using dynamic viscosity measurements, FTIR spectroscopy and Multiple Stress Creep Recovery (MSCR) testing. The obtained results demonstrated that corn starch significantly affected both the rate and temperature dependence of aging. The effect of corn starch was strongly dependent on both the aging temperature and modifier dosage, indicating that starch does not uniformly inhibit all aging processes but rather modifies their kinetics in a process-specific manner. Increasing the aging temperature from 100 to 140 °C accelerated the viscosity growth by approximately 9–11 times, depending on the binder composition. The apparent rate constants for carbonyl formation ranged from 9 × 10−6 to 7 × 10−5 h−1 for the reference binder and from 1 × 10−5 to 5 × 10−5 h−1 for starch-modified binders. The calculated apparent activation energies varied between 1.31 and 67.6 kJ mol−1, confirming that starch altered the temperature sensitivity of oxidation and structural transformation reactions. Among the investigated formulation (4–8 wt.% corn starch), the binder containing 4 wt.% corn starch exhibited the most favorable balance between aging resistance and production cost. Overall, the results demonstrate that corn starch modifies rather than universally inhibits bitumen degradation, with the optimum performance depending on the investigated aging parameter, modifier dosage and aging temperature, with 4 wt.% providing the most favorable overall balance between chemical aging behavior, rheological performance and production cost.

Materials doi: 10.3390/ma19153300

Authors: Yaojia Ren Jingru Wang Jiajun Xu Yingkang Wei Jilei Zhu Qingge Wang Jianyong Wang Shifeng Liu Solomon-Oshioke Agbedor

To address the strength–ductility trade-off in titanium alloys, a comparative study was conducted on Ti-6Al-4V (TC4) alloys fabricated by laser powder bed fusion (L-PBF) and electron beam powder bed fusion (EB-PBF). The L-PBF specimen primarily consisted of acicular α′ martensite with high residual stress. In contrast, the EB-PBF specimens, owing to a substrate preheating temperature of 740 °C and a reduced cooling rate (103~105 K/s), exhibited a stable and coarse α + β lamellar structure. Combined with the high oxygen content (0.24 wt.%) that provided solid-solution strengthening, this morphology enabled simultaneous attainment of a yield strength of 1120 ± 12 MPa and an elongation at fracture of 11.1 ± 1.3%. Notably, deformation-induced HCP→FCC phase transformation occurred in EB-PBF alloys, generating a dual-phase HCP/FCC structure that effectively accommodated plastic strain. These results highlight the superior potential of EB-PBF over L-PBF for fabricating titanium alloys with an exceptional strength–ductility synergy.

Materials doi: 10.3390/ma19153299

Authors: Shouju Miao Jun Chen Zhihai Zhang Shuirong Gui Ling Zhou Shengjie Liu

Bored pile waste slurry generated during bridge substructure construction exhibits high water content and stable colloidal properties, resulting in difficult solid–liquid separation and severe environmental risks. To improve solid–liquid separation and facilitate efficient disposal, this study systematically investigated the flocculation and dewatering performance of the slurry using three typical flocculants (Anionic polyacrylamide (APAM), cationic polyacrylamide (CPAM), and polymeric aluminum chloride(PAC)) through sedimentation tests, supernatant purification monitoring, particle size analysis, zeta potential measurements, and specific filtration resistance tests. The results show that flocculant type and dosage significantly affect treatment efficiency. Organic flocculants outperform inorganic PAC in both particle aggregation and dewatering improvement. Among them, APAM exhibits a prominent low-dose advantage; at an optimal dosage of 0.2–0.3% (corresponding to a pure reagent dosage of 10–15 mg/L based on wet slurry), it effectively reduces the slurry water content and lowers supernatant suspended solids below the 50 mg/L discharge standard within 80 min. Mechanistically, PAC provides primarily electrostatic neutralization, whereas APAM and CPAM achieve composite flocculation through charge neutralization, adsorption bridging, and sweep capture. Benefiting from efficient low-dose neutralization and long-chain bridging effects, APAM significantly reduces filtration resistance and forms stable flocs. Overall, an APAM dosage of 10–15 mg/L is the optimal scheme for in situ treatment of bored pile waste slurry, providing technical support for the efficient management and controlled disposal of engineering slurry under similar geological conditions.

Materials doi: 10.3390/ma19153298

Authors: Hongwei He Zhuo Liu Junnan Fan Xuke Dai Xuquan Huang Jun Wang Xiaorong Zhao Haojie Wang Fei Xue Yuwei Xiang

This study investigates the conditioning and deep dewatering of pyrite tailings slurry using a composite system comprising polyferric chloride (PFC), polydiallyldimethylammonium chloride (PDMDAAC), and fly ash as a skeleton builder. The synergistic application significantly enhanced solid–liquid separation, reducing the filter cake moisture content to 53.6% and the capillary suction time (CST) to 15.1 s. Based on settling and dewatering kinetics, the optimal dosages were established as 5 g/L PFC, 10 mL/L PDMDAAC, and 20 g/L fly ash. Characterization via SEM, XPS, and FTIR elucidated the underlying mechanisms: PDMDAAC facilitated fine particle aggregation through charge neutralization and adsorption bridging, while PFC hydrolysis products reinforced the floc architecture via hydroxyl complexation and sweep flocculation. Crucially, fly ash constructed a robust skeletal framework with efficient drainage channels within the filter cake, effectively mitigating pore clogging. This study provides a high-performance conditioning strategy facilitating the resource utilization of pyrite tailings.

Materials doi: 10.3390/ma19153296

Authors: Yao Yang Hui Li Haijun Wang Lei Dong Haile Yan Haitao Fan Bingqi Tian

This study proposes a prediction method for ceramic matrix composite thin plates (CMCTPs) with protective coatings under high-temperature conditions, based on the first-order shear deformation theory and the energy principle while considering thermal effects. It can successfully predict the variations in natural frequencies and resonant responses of CMCTPs over the experimentally validated temperature range of 25 °C to 800 °C, using a thermo-vibrational platform with a maximum temperature capability of 1500 °C. In addition, a thorough investigation of multiple key parameter influences on the dynamic characteristics of CMCTPs with and without coating is performed, with special focus on the effect of the coating on enhancing the thermo-vibrational resistance of such structures. The analytical results demonstrate that the protective coating significantly enhances the thermo-vibrational resistance of the structure. Optimization of the coating-to-substrate thickness ratio, elastic modulus ratio, and thermal expansion coefficient ratio is recommended to maximize vibration suppression performance, providing critical guidance for the dynamic design of coated CMCTP components in aerospace.

Materials doi: 10.3390/ma19153297

Authors: Zbigniew Kolakowski Andrzej Teter

This study investigates the buckling behaviour of thin-walled rectangular laminated plates under complex in-plane loading. Linear variations in the normal transverse load components and parabolic variations in the shear load components are assumed on the plate edges. The in-plane load distributions reproduce the design solutions reported in the literature. The starting point for the considerations in this study is the classical laminated plate theory (CLPT). It focuses on cases when the laminate coupling stiffness B-submatrix components are non-zero. Six cases of in-plane loading in the pre-buckling stage are investigated. Ten examples of plates made of general laminates with different stacking sequences and the same thickness are tested. The effect of selected components of the coupling B-submatrix on the stability of the rectangular laminated plates is determined. Eigen-problem solutions for the laminated plates are obtained under complex in-plane loading, demonstrating that the proper assessment of eigen-values must include a detailed analysis of all stiffness matrix components and reduction coefficients in beam modelling. For all cases investigated in this study, the inclusion of the B-submatrix decreases the bifurcation loads.

Materials doi: 10.3390/ma19153295

Authors: Henok Dereje Nega Hailu Shimels Gebremedhen Tomasz Trzepieciński Fasikaw Kibrete Temesgen Tadesse Feisa Dereje Engida Woldemichael

Structural applications require materials that provide an optimal balance of strength, durability, and sustainability. This study develops functionally graded sisal/glass fiber-reinforced polymer composites and evaluates their tensile, compressive, and flexural properties, as well as their water absorption behavior. First, an experimental approach was adopted in which sisal fibers were treated with a 6% sodium hydroxide (NaOH) solution to improve fiber–matrix adhesion. The composites were fabricated using the hand lay-up method with varying sisal fiber ratios. Mechanical testing showed that the composites achieved a tensile strength of 146 MPa for the rectangular specimens and 199.5 MPa for the composite bars. The highest compressive strength (120 MPa) and flexural strength (326 MPa) were observed at 20% sisal fiber content. In addition, finite element analysis (FEA) results showed maximum tensile and compressive strengths of 181.24 MPa and 147.57 MPa, respectively, and were in reasonable agreement with the experimental results. Moreover, water absorption studies showed a direct correlation between fiber content and moisture uptake, with values of 1.40% (10% sisal), 2.55% (20%), and 3.85% (30%). The results indicate that functionally graded sisal/glass fiber-reinforced composites exhibit superior mechanical properties compared with conventional composites. The graded structure enhances design flexibility, optimizing material performance for structural applications. These findings highlight the potential of functionally graded composites as a sustainable alternative that addresses the limitations of traditional materials while promoting more efficient and environmentally friendly engineering solutions.

Materials doi: 10.3390/ma19153294

Authors: Ayechew Aklilu John Belding Joe Strauss Brett D. Ellis

This study empirically and numerically investigates sintering-induced shrinkage of 316L stainless steel cylinders fabricated via Bound Metal Deposition (BMD). Sintering shrinkages were measured for three cylindrical specimens, one each in x-, y-, and z-print orientations, via a dilatometer. Each specimen was horizontally sintered to 1360 °C via a prescribed temperature profile to maintain identical sintering conditions between specimens. Numerically, a two-dimensional axisymmetric finite element model was implemented in Abaqus using a user-defined viscoplastic constitutive model incorporating porosity- and temperature-dependent viscosities, grain-growth kinetics, and capillary-driven sintering stress. Model parameters were calibrated using particle swarm optimization by minimizing a combined error metric for temperature-dependent shrinkage responses and final relative densities. Results indicate: (1) final shrinkages of 13.5%, 13.7%, and 14.3% for the x-, y-, and z-oriented specimens, respectively, and (2) the optimized numerical model utilizing literature-informed material property constraints results in shrinkages and final densities that are in good agreement with empirical observations. Importantly, this work (1) suggests sintering shrinkage may depend on print orientation, in addition to furnace orientation, for BMD-fabricated 316L stainless steel, and (2) adds an initial dilatometer data set for BMD 316L to the literature. More broadly, this work supports future design activities via an experimental and numerical characterization of sintering behavior.

Materials doi: 10.3390/ma19153293

Authors: Bartłomiej Krawczyk Piotr Szablewski Sylwia Wencel

This research evaluates the accuracy and repeatability of a novel procedure for measuring pitch diameter using a touch-trigger probe in a production environment. Experiments were performed on a WFL M40 machine equipped with a Renishaw RMP600 strain gauge probe, using different thread types and machine tools. The results were validated by comparison with the traditional three-wire method, which is regarded as a high-precision reference for pitch diameter measurement. Statistical analyses, including the Shapiro–Wilk test, ANOVA, and Tukey HSD post hoc tests, were applied to assess error distribution and differences between thread types and machines. The proposed method demonstrated satisfactory accuracy and repeatability, with an error spread of approximately ±0.015 mm, achieving measurement results within the manufacturing tolerance range (±0.07 mm). The study also showed that measurement accuracy is influenced by factors such as thread angle and Z-axis positioning. Overall, the method proved to be reliable for production use, offering a good balance between measurement accuracy and operational efficiency, although minor adjustments may be needed for automatic correction routines.

Materials doi: 10.3390/ma19153292

Authors: Wanliang Zhang Kaiyu Zhang Chengshuang Zhou Lin Zhang

A Fe5Cu5V30Ti30Nb30 high-entropy alloy film was designed as a Cr- and Al-free metallic sensing layer for thin-film strain gauges in high-pressure hydrogen environments. CALPHAD calculations predicted a BCC/B2-type phase field, while XRD, EBSD and GIXRD results supported a BCC-type structure without direct confirmation of long-range B2 ordering. Fe5Cu5V30Ti30Nb30 films deposited on Si reference substrates at 150 and 300 W retained broad BCC-type diffraction features. The 300 W film showed a more continuous cross-sectional morphology, good metallic conductivity and a comparable nanomechanical response with slightly higher hardness. Device-level tests were then performed using Cr/AlN/Fe5Cu5V30Ti30Nb30 TFSGs on 316L stainless-steel substrates. The devices exhibited average absolute apparent zero shifts of 16.08 με in 12 MPa N2 and 17.79 με in 12 MPa H2, with an additional H2-associated apparent response of only 1.71 με. Static tensile tests in 12 MPa H2 confirmed a linear strain response with a gauge factor of 1.72 ± 0.01.

Materials doi: 10.3390/ma19153291

Authors: Emanuel Ewerton Mendonça Vasconcelos Maria Clara Müller de Andrade André Galembeck Gabriela Queiroz de Melo Monteiro Fernanda Donida Ortigoza Luís Felipe Espíndola-Castro

Although the modification of resin composites with antimicrobial agents represents a viable alternative for biofilm inhibition, these changes may compromise the optical and mechanical properties of dental restorations. This in vitro pilot study evaluated the effect of incorporating Nano-Silver Fluoride (NSF) containing 2000 ppm silver nanoparticles (AgNPs) on the microhardness and color of flowable resin composites: Vittra APS Unique Flowable (VA), Filtek Bulk Fill Flowable (FB), and Filtek Supreme Flowable (FS). The resin composites were modified by adding 1 wt%, 2 wt%, and 4 wt% NSF and compared with an unmodified group (control). NSF was characterized by UV–visible spectroscopy and transmission electron microscopy. The specimens were subjected to Vickers microhardness testing and color analysis using the CIEDE2000 (ΔE00) and CIELAB (ΔE) systems. NSF incorporation had a material-dependent effect on microhardness. The VA group showed a progressive reduction in microhardness with increasing NSF additions, whereas the FS group remained unchanged up to the concentration of 2 wt%, and the FB group showed no significant reduction in microhardness at any of the tested concentrations compared with the control (p = 0.549). All resin composites exhibited clinically relevant color changes that increased with the NSF concentration, with more pronounced color changes in the VA group, whereas FB and FS did not vary significantly with the addition of different NSF concentrations. Overall, NSF mainly affected the optical properties, with esthetic limitations being the main challenge to be overcome in further studies. The FB and FS groups at 1 wt% and 2 wt% showed smaller chromatic changes than VA, without compromising microhardness, and appear promising for future investigations, including antimicrobial and cytotoxicity analyses.

Materials doi: 10.3390/ma19153290

Authors: Gisuk Hong Jaebong Cho Hyunbo Cho

Melt-pool depth governs interlayer bonding and porosity in laser powder bed fusion and underpins part qualification, yet predicting it reliably remains difficult. Fast conduction models reach useful accuracy only after the absorptivity is fitted to the depths they are meant to predict, and inverse analyses have been used the same way, to recover a calibrated parameter rather than to test the model. Here, the absorptivity is fixed independently instead, a measured coupling for IN718 and, for IN625 and 316L, a published closed-form relation never fitted to the present depths. This converts a moving-source conduction model from an object of calibration into one of validation. The melt boundary is located by root-finding rather than on a grid, so no discretization error enters the diagnosis. Across 231 single tracks, the model reproduces conduction-regime depth and half-width to within a few percent and underpredicts increasingly once keyholing begins. Inverting each measured depth for the absorptivity conduction would require yielding a fitting-free diagnosis: no conduction-regime track demands a non-physical value, and the inferred value converges near 0.38 against inputs of 0.27 to 0.34, whereas every keyhole-classified track demands a value above unity. Because an inferred absorptivity also absorbs unmodeled transport, downward convection was emulated as an anisotropic effective diffusivity; at the enhancement reported for Marangoni flow, no keyhole track becomes explicable. A measured Ti-6Al-4V absorptivity rise of a factor 1.9 supports the mechanism. An enthalpy-indexed correction and data-driven baselines remain alloy-specific, whereas the physics-based model retains its advantage under cross-alloy extrapolation. All findings are for single tracks on bare plates.

Materials doi: 10.3390/ma19153289

Authors: Ping Gao Qinglong You Jinbo Xie Xi Du Yungui Pan Bo Lu Lixin Chang

Concrete exposed to sub-zero and elevated temperatures exhibits strongly non-monotonic mechanical behavior governed by different physical mechanisms. Existing thermo-mechanical constitutive models commonly account for temperature-dependent degradation, but many are formulated for a specific temperature regime, and explicit treatment of reversible freezing-induced strengthening and irreversible high-temperature damage within a single constitutive structure remains limited. This study develops a unified thermo-elastoplastic damage model for concrete over the temperature range from −40 to 800 °C within the framework of irreversible thermodynamics. Plasticity is formulated in the effective-stress space, while compressive damage is driven by the damage energy release rate. Temperature effects are incorporated through evolution laws for compressive strength, elastic modulus, peak strain, and the shape parameters of the ascending and descending branches. Ice-induced strengthening is represented through reversible modifications of stiffness and strength thresholds, whereas high-temperature dehydration and microcracking are represented through irreversible thermal damage. The model was calibrated using published low-temperature compression data for C30–C50 concrete and complete high-temperature stress–strain curves for normal-strength concrete. The normalized curve-shape laws were subsequently assessed using high-strength concrete curves after normalization by their measured peak stress and peak strain, while selected components of the three-dimensional extension were assessed using residual HSC60 true-triaxial data. The calibrated model represented the freezing-point strength valley, sub-zero strengthening and embrittlement, non-monotonic strength evolution at intermediate temperatures, and progressive high-temperature ductilization. Complete high-temperature normal-strength concrete curves were reproduced with R2 values of 0.94–0.99, while the normalized multiaxial strength assessment yielded an average relative error of approximately 8%. These results support the internal consistency of the formulation and the limited cross-strength-grade applicability of the normalized curve-shape laws, rather than unrestricted predictive capability. Further independent experiments are required before application beyond the material, moisture, thermal-history, and loading conditions represented by the available datasets.

Materials doi: 10.3390/ma19153287

Authors: Huadong Cui Yuhao Shang Hanying Shou Leiting Ye Ji Yuan Peixuan He Ruige Li Haijie He Zihang Ding Ziyu Mao

Expanded polystyrene concrete (EPSC) offers low density and thermal insulation but is limited by brittle flexural failure. This study evaluates whether high-toughness modified polypropylene (HTPP) fibers can improve the post-cracking response of EPSC and translate the material-level gains into exterior wall-panel design under wind loading. Six mixtures containing 0, 0.3, 0.6, 0.9, 1.2, and 1.5 vol% HTPP fibers were prepared. Compressive tests, four-point bending tests, and scanning electron microscopy were conducted. Flexural toughness was assessed using average residual flexural strength together with the Nemkumar, literature-based, JSCE-SF4, and modified PCER methods. The mechanical indices generally increased and then declined as fiber content rose, with the best overall performance at 0.9 vol%. Relative to plain EPSC, this mixture increased compressive strength by 21.5%, flexural strength by 277.2%, and average residual flexural strength by 681.3%. The four toughness evaluation approaches produced consistent trends and showed that HTPP fibers most strongly improved post-peak load retention and energy absorption. Microscopic observations indicated that fiber bridging, crack-path deflection, stress transfer, and interfacial energy dissipation contributed to the enhanced toughness, whereas excessive fiber addition reduced the benefits. Using the measured residual capacity in a wind-load design model showed that HTPP fiber reinforcement can enlarge the allowable unsupported span of EPSC exterior wall panels. These findings identify an effective fiber dosage and provide a basis for the structural use of lightweight EPSC panels.

Materials doi: 10.3390/ma19153286

Authors: Janusz Torzewski Tomasz Helt Robert Kosturek Michal Jambor Michal Černý Janusz Mierzyński Marcin Wachowski

This paper investigates the microstructural evolution and mechanical performance of dissimilar friction stir-welded (FSW) T-joints produced from AA5083-H111 and AA7020-T651 aluminium alloys. The study focuses on the effects of tool rotational speed, traverse speed, and tool pin length on joint quality and mechanical strength. Welding experiments were conducted at two rotational speeds (400 and 700 rpm) and three traverse speeds (50, 100, and 200 mm/min) using two Triflute tools with pin lengths of 4.8 mm and 6.8 mm. The welded joints were examined by macro- and microstructural observations, microhardness measurements, and bending tests performed under pull-out loading conditions. The results showed that the use of the longer pin significantly improved material mixing and reduced the extent of internal defects, resulting in higher bending strength. Increasing the traverse speed improved the mechanical performance, whereas an excessively high rotational speed reduced joint strength due to increased heat input and unfavourable microstructural changes. Microhardness profiles showed no reduction in hardness within the heat-affected zones relative to the base materials and indicated localised hardening in the stir zone. For the investigated material configuration and tool geometries, the highest joint strength was obtained at a rotational speed of 400 rpm and a traverse speed of 200 mm/min using the longer-pin tool. The study confirms the critical role of process parameter optimisation and tool geometry in producing high-quality dissimilar FSW T-joints suitable for lightweight structural applications.

Materials doi: 10.3390/ma19153288

Authors: Damian Sokołowski Tomasz Wudkiewicz

This study presents a materials-oriented, code-based parametric optimization of the load-bearing steel tubular arch girder in a tied-arch footbridge inspired by the Father Bernatek Footbridge in Krakow. The objective was to reduce structural steel demand by minimizing the arch-girder weight under Eurocode load combinations with ultimate limit state (ULS) and serviceability limit state (SLS) constraints, while accounting for discrete tubular cross-section changes within a realistic finite element model. A semi-automated workflow linked Autodesk Dynamo, Python scripts, and Autodesk Robot Structural Analysis to generate bridge geometry, build the finite element method (FEM) model, apply code-based loads and combinations, and evaluate structural response using a discrete, non-gradient-based search. A preliminary sensitivity screening was performed for the full set of design parameters, while the final optimization was governed mainly by arch rise, hanger number, and ULS-controlled discrete arch cross-section changes. The optimization reduced the arch-girder weight by 10.7% relative to the reference configuration, from 360.3 × 103 kg to 321.6 × 103 kg, within the adopted design domain. The optimum solution corresponded to an arch rise of 23.4 m, 31 hangers, and a deck spacing of 6.0 m. Hanger arrangement strongly affected force redistribution in the arch girder, while the final optimum was controlled by code-based utilization thresholds. The results show that an application programming interface (API)-driven parametric workflow can support early-stage optimization of tied-arch footbridges under code-based design constraints. The scientific contribution of the study lies not in automating Eurocode verification alone, but in identifying the structural mechanisms that govern the minimum-weight solution, including the interaction between arch rise, hanger arrangement, force redistribution, ULS utilization, and discrete tubular cross-section changes.

Materials doi: 10.3390/ma19153284

Authors: Wei Gao Jun Zhu

Compression–torsion coupled metamaterials provide a geometry-driven approach for motion conversion and wave regulation. This study proposes a spatial curved-rod compression–torsion coupled metastructure and develops a reduced-order equivalent stiffness model with axial displacement and rotational angle as the generalized degrees of freedom. The equivalent stiffness matrix, derived from the curved-rod centerline geometry through a strain-energy formulation, is incorporated into a one-dimensional Bloch model to characterize low-frequency wave propagation. The results show that the off-diagonal coupling stiffness governs the compression-induced rotational response of the unit cell and significantly affects the frequencies and modal compositions of the two lowest dispersion branches. Finite element simulations and experiments validate the predicted stiffness and compression–torsion response, while acceleration transmissibility measurements of a finite periodic chain are consistent with the theoretical dispersion characteristics. The reduced-order model captures the overall behavior of the two lowest branches and clarifies the role of compression–torsion coupling stiffness in branch separation and modal composition, although the higher branch is less accurately predicted owing to the lumped inertia approximation. The proposed design provides a lightweight strategy for low-frequency wave regulation through structural coupling.

Materials doi: 10.3390/ma19153285

Authors: Yongli Luo Long Fan Bin He Xing Fan Facheng Qiu Renlong Liu

Polyurethane adhesives often suffer from high viscosity, poor flowability, and limited mass transfer efficiency, making it challenging for conventional single-shaft or twin-shaft mixing systems to achieve uniform mixing in large-capacity equipment. This study investigates the differential speed coupling mechanism of a 600 L eccentric four-shaft mixer for high-viscosity polyurethane adhesive systems using computational fluid dynamics (CFD). The effects of different differential speed ratios on flow field evolution and mixing performance were systematically analyzed through multiple indicators, including power consumption per unit volume, velocity variation coefficient, effective mixing region ratio, vortex core coverage, and maximum Lyapunov exponent (LLE). Among the investigated conditions, the 50:100 differential speed ratio exhibited a more favorable circulation pattern, forming a closed-loop circulating flow field in the entire reactor, with an effective mixing region accounting for 60%, a velocity variation coefficient of only 0.38, and a power consumption per unit volume as low as 21.2 W/m3. A constant speed of 100:100 easily generates dead zones in the interaxial flow field, while a high differential speed of 100:50 leads to excessive disturbances and energy waste. Moderate differential speed can generate large-scale coupled vortices, thereby enhancing mixing through coupled axial transport, radial dispersion, and tangential shear. An eccentric four-shaft mixer combined with reasonable differential speed control can effectively improve flow field uniformity and reduce potential mixing limitations in large-scale polyurethane adhesive systems. Among the three investigated differential speed ratios, the 50:100 condition exhibited the most favorable overall mixing performance. These findings provide numerical insights into the selection of differential speed operating conditions for high-viscosity polyurethane adhesive mixing systems.