Materials

21 pages, 4133 KB

Open AccessArticle

A Cascaded Classification–Regression Framework for Shear Strength Prediction of Cold-Formed Steel Screw Connections

by Shen Liu, Rui Ren, Xiguang Liu and Zheng Luo

Materials 2026, 19(12), 2668; https://doi.org/10.3390/ma19122668 (registering DOI) - 21 Jun 2026

Existing AISI S100 provisions for cold-formed steel (CFS) screw connections lack codified strength equations for screw shear and net section fracture, and traditional machine learning (ML) models struggle to predict these minority failure modes due to imbalanced experimental datasets. This study proposes a [...] Read more.

Existing AISI S100 provisions for cold-formed steel (CFS) screw connections lack codified strength equations for screw shear and net section fracture, and traditional machine learning (ML) models struggle to predict these minority failure modes due to imbalanced experimental datasets. This study proposes a cascaded ML framework that first classifies the failure mode and then predicts strength using mode-specific regressors. Two cascade strategies are evaluated: a Hard Classification Cascade (HC-C) and a novel Probability-Weighted Cascade (PW-C) that weights predictions by class probabilities to mitigate error propagation from misclassification. The predictive performance of the two cascaded models is benchmarked against a single regressor without classification. The superior PW-C model is then compared with AISI S100, and its resistance factor ϕ is subsequently calibrated in accordance with LRFD. Results show that the proposed cascaded models outperform the direct regression model, with PW-C improving the R² for minority-class screw shear from 0.765 to 0.933 and for net section fracture from 0.784 to 0.912. Compared with AISI S100 provisions, PW-C extends coverage to the currently unaddressed failure modes and effectively captures screw group effects on shear strength based on a database of 564 tests. Reliability analysis yields an overall ϕ_c of 0.64 for the PW-C model, with a recommended divisor of 1.15 for direct application within the AISI design framework. This work provides a practical, data-driven pathway for updating design codes to cover failure modes beyond current specification limits. Full article

(This article belongs to the Section Construction and Building Materials)

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17 pages, 12997 KB

Open AccessArticle

Effect of Pore Structure Parameters on Thermal Insulation Performance of Porous Ceramics Fabricated by Material Jetting

by Qintao Shen, Peng Wang, Chunan Song, Chao Ding, Yapeng Ning, Viboon Saetang, Mengji Shen, Yaxuan Wei, Jiying Wang, Renquan Ji, Xin Yang and Huan Qi

Materials 2026, 19(12), 2667; https://doi.org/10.3390/ma19122667 (registering DOI) - 21 Jun 2026

Abstract

Porous ceramics have shown great application potential in aerospace, electronics, and lithium-ion battery thermal management due to their low density, high specific strength, and excellent thermal insulation. Material Jetting (MJ), a high-precision 3D printing technology, enables the fabrication of porous ceramics with tailored [...] Read more.

Porous ceramics have shown great application potential in aerospace, electronics, and lithium-ion battery thermal management due to their low density, high specific strength, and excellent thermal insulation. Material Jetting (MJ), a high-precision 3D printing technology, enables the fabrication of porous ceramics with tailored pore structures, but the synergistic effects of pore structure parameters (configuration, porosity, and number of periods) on their thermal insulation performance remain insufficiently explored. This study systematically investigates the thermal insulation behavior of zirconia porous ceramics fabricated by MJ through experimental tests and numerical simulations. Three typical lattice configurations (Octet, Schwarz, and Gyroid) were selected, and samples with varying porosities (40%, 50%, 60%) and numbers of periods (1, 2, 3) were prepared. The results indicate that the Octet configuration (60% porosity, 3 periods) exhibits the optimal thermal insulation performance, with a minimum cold-end temperature of 58.5 °C (experiment) and 59.21 °C (simulation), attributed to its strut-based structure that forms a more tortuous heat conduction path. For the Gyroid configuration, thermal insulation performance improves with increasing porosity (reducing solid conduction dominance under non-forced convection) and decreases with decreasing number of periods (due to inhomogeneous pore distribution extending heat transfer paths). Notably, the trend of porosity affecting thermal insulation is opposite to that of compressive performance. Numerical simulation results are consistent with experimental data in both values and trends, verifying the reliability of the model. This work clarifies the key factors regulating the thermal insulation of MJ-fabricated porous ceramics and provides practical structural design guidelines for applications such as lithium-ion battery thermal runaway management. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

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20 pages, 3929 KB

Open AccessArticle

Multi-Technique Characterization of Historic Blue Bricks from Beijing: Compositional Grouping, Weathering Assessment, and Conservation Implications

by Zhaoyang Zhu, Rui Hu and Bo Zhang

Materials 2026, 19(12), 2666; https://doi.org/10.3390/ma19122666 (registering DOI) - 21 Jun 2026

Abstract

Historic blue bricks are fundamental to Beijing’s architectural heritage, yet cross-site compositional data for guiding material-compatible restoration remain scarce. This study applies WD-XRF, XRD, SEM, thermal expansion measurement, and physical property testing to 21 blue brick specimens from four Beijing-area sites spanning the [...] Read more.

Historic blue bricks are fundamental to Beijing’s architectural heritage, yet cross-site compositional data for guiding material-compatible restoration remain scarce. This study applies WD-XRF, XRD, SEM, thermal expansion measurement, and physical property testing to 21 blue brick specimens from four Beijing-area sites spanning the Tang through Qing dynasties, with PCA and K-means clustering used to explore compositional grouping structures. Within this exploratory dataset, a compositional distinction separates the Ming and Qing Great Wall bricks: CaO falls from 7.7 to 1.5 wt.% as anorthite gives way to albite, while Qing specimens are denser (1.79 vs. 1.65 g·cm⁻³) with lower water absorption (15.9% vs. 20.9%). Two Wanping City bricks are strongly sulfate-enriched (SO₃ up to 9.8%), and WP-SE3 additionally carries a heavy chloride load (Cl 2.1%), masking their original clay signatures and illustrating how unrecognized weathering can distort compositional grouping and source-related interpretation from bulk chemistry. K-means clustering yields compositional types that overlap only partially with site boundaries, capturing raw material variation rather than site-specific manufacturing fingerprints. Despite constraints in sample size and physical property coverage, the integrated dataset offers preliminary compositional benchmarks and limited performance data to inform period-specific brick replacement at these heritage sites. Full article

(This article belongs to the Special Issue Advanced Materials for Heritage and Archaeology (Third Edition))

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21 pages, 17728 KB

Open AccessArticle

Dependence of Tensile Ductility and Impact Toughness on Constituent Particles in 2014 Aluminum Alloy

by Geng Chen, Fang Li, Sijun Chen, Songyi Chen and Kanghua Chen

Materials 2026, 19(12), 2665; https://doi.org/10.3390/ma19122665 (registering DOI) - 21 Jun 2026

Abstract

In contemporary engineering applications, deficiencies in dynamic mechanical properties, particularly impact toughness, are the leading cause of fracture incidents. Consequently, inadequate dynamic mechanical properties have emerged as the primary constraint limiting the further commercial application of precipitation-strengthened high-strength aluminum (Al) alloys, exemplified by [...] Read more.

In contemporary engineering applications, deficiencies in dynamic mechanical properties, particularly impact toughness, are the leading cause of fracture incidents. Consequently, inadequate dynamic mechanical properties have emerged as the primary constraint limiting the further commercial application of precipitation-strengthened high-strength aluminum (Al) alloys, exemplified by the 2014 aluminum alloy. Since the dynamic mechanical properties of the 2014 wrought aluminum alloy are fundamentally governed by the decohesion and cracking of coarse second-phase constituent particles, it is necessary to quantify the correlation between microstructure and mechanical properties. Meanwhile, the size and volume fraction of constituent particles are largely dictated by the concentration of main and impurity alloying elements. Experimental results revealed that the volume fraction of coarse constituents increased with increasing Cu, Si, and Fe content, and that tensile ductility and impact toughness decreased following an inverse exponential relationship with the volume fraction of constituents. The aim of this study is to establish a quantitative relation to correlate the characteristics of coarse constituents with the tensile ductility and impact toughness of the 2014 aluminum alloy. A mathematical model was developed by regarding the coarse constituents as ellipsoidal inclusions. Their volume fraction and aspect ratio were considered in the model. Model predictions show broad agreement with experimental data. These properties are more sensitive to the volume fraction when it is low. Conversely, a larger aspect ratio leads to higher ductility and toughness. The sensitivity is also greater at a small aspect ratio. The model further indicates that reducing the volume fraction when it is high yields limited improvement, whereas further reduction at a low volume fraction leads to significant enhancement of ductility and toughness. This study correlates coarse constituent characteristics with tensile ductility and impact toughness quantitatively, and provides a theoretical framework for predicting and optimizing the mechanical properties of 2014 aluminum alloy. Full article

(This article belongs to the Section Materials Simulation and Design)

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19 pages, 7412 KB

Open AccessArticle

Influence of Mix Composition on the Microstructural Evolution of Leached Cement Pastes

by Kailai Zhang, Wenwei Li, Huamei Yang, Dan Tian, Jinyang Cui, Hao Wang and Fan Li

Materials 2026, 19(12), 2664; https://doi.org/10.3390/ma19122664 (registering DOI) - 21 Jun 2026

Abstract

Calcium leaching increases the hydraulic concrete material’s porosity and the diffusion coefficient, thereby jeopardizing engineering safety. Fly ash and silica fume are commonly used mineral admixtures in hydraulic concrete, and their effects on the material’s leaching characteristics, especially its microstructural and transport properties, [...] Read more.

Calcium leaching increases the hydraulic concrete material’s porosity and the diffusion coefficient, thereby jeopardizing engineering safety. Fly ash and silica fume are commonly used mineral admixtures in hydraulic concrete, and their effects on the material’s leaching characteristics, especially its microstructural and transport properties, require further investigation. In this study, calcium leaching tests were conducted on cement paste (CP), silica fume–cement paste (SF), and fly ash–cement paste (FA) using a 6 mol/L ammonium chloride solution to accelerate the leaching process. Subsequently, a series of quantitative and qualitative analyses was performed on the deteriorated specimens, including phenolphthalein indicator spraying, X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM). Additionally, the diffusion coefficients of the material at different locations were calculated and analyzed. The results show that partially replacing cement with silica fume or fly ash increases the initial porosity, gel pore content, and initial diffusion coefficients. After 28 days of leaching, compared to the initial values, the porosity increases in the 0–4 mm layer from the leached surface were 83.6% for CP, 11.0% for SF, and 39.0% for FA. The diffusion coefficients increased by factors of 14.3 (CP), 6.1 (SF), and 13.6 (FA), indicating enhanced resistance to leaching. The primary reason for this is that the reactive silica in the admixtures undergoes a pozzolanic reaction with the calcium hydroxide generated by cement hydration, producing additional calcium silicate hydrate (C-S-H) gel, which reduces the capillary pores that would otherwise result from calcium hydroxide decomposition. Full article

(This article belongs to the Special Issue Sustainable Construction and Building Materials: Microstructure, Mechanical Performance, and Long-Term Durability)

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10 pages, 1828 KB

Open AccessCommunication

Phase Engineering of TiO₂/MXene Heterostructure Nanosheets for Enhanced Photocatalysis

by Yuntao Huang, Zibo Chen, Zhenyu Gong, Zhihong Dai, Cheng Chen and Daping He

Materials 2026, 19(12), 2663; https://doi.org/10.3390/ma19122663 (registering DOI) - 20 Jun 2026

Abstract

TiO₂-based heterostructures have attracted considerable attention in photocatalytic pollutant degradation owing to their enhanced photoresponse and improved charge separation. The phase structure of TiO₂ strongly affects its band structure and interfacial charge-transfer behavior, making phase structure control critical for optimizing [...] Read more.

TiO₂-based heterostructures have attracted considerable attention in photocatalytic pollutant degradation owing to their enhanced photoresponse and improved charge separation. The phase structure of TiO₂ strongly affects its band structure and interfacial charge-transfer behavior, making phase structure control critical for optimizing photocatalytic performance. However, due to the small difference in free energy among TiO₂ phase structure and the strong dependence of TiO₂ nucleation and growth on the local reaction environment, it remains challenging to precisely control the phase structure of TiO₂ in the TiO₂-based heterostructure nanomaterials. Herein, we achieved the phase engineering of TiO₂/MXene heterostructure nanomaterials through a solvent-regulation strategy. Specifically, by regulating the acetonitrile/water ratio in the hydrothermal solvent, TiO₂ with distinct phase structures was in situ grown on hydrothermally treated MXene nanosheets, resulting in two representative TiO₂/MXene heterostructure nanosheets: anatase TiO₂/MXene and rutile TiO₂/MXene. Acetonitrile likely acted as a surface-adsorbing agent during TiO₂ formation, stabilizing the anatase phase and promoting the preferential formation of anatase TiO₂. Benefiting from the optimized heterostructure, TiO₂/MXene heterostructure nanosheets promoted the generation of singlet oxygen (¹O₂), leading to enhanced photocatalytic degradation. Full article

(This article belongs to the Topic Advanced Materials in Chemical Engineering)

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27 pages, 11202 KB

Open AccessArticle

Simulation and Experimental Study on Parameter Optimization for the Glass Molding Process of Automotive Panoramic Roofs

by Ruili Wang, Hongyan Wang, Na Xiao, Zihao Hu, Wenjun Tong, Xiaohong Yang and Wuyi Ming

Materials 2026, 19(12), 2662; https://doi.org/10.3390/ma19122662 (registering DOI) - 20 Jun 2026

Abstract

The automotive panoramic roof exhibits a large-size and thin-wall geometry, with a length-to-thickness ratio approaching the thousand level. This geometric feature makes its forming quality highly sensitive to forming conditions. During the glass molding process, variations in temperature evolution, loading, and cooling parameters [...] Read more.

The automotive panoramic roof exhibits a large-size and thin-wall geometry, with a length-to-thickness ratio approaching the thousand level. This geometric feature makes its forming quality highly sensitive to forming conditions. During the glass molding process, variations in temperature evolution, loading, and cooling parameters may lead to residual stress accumulation and springback deformation, thereby affecting dimensional accuracy and final forming quality. In this study, a full-process finite element model was established and combined with an L16(4^5) orthogonal design to investigate the effects of five key process parameters—heating temperature, holding time, quenching air velocity, quenching air pressure, and quenching time—on the mean residual stress and mean springback displacement in the glass molding process (GMP). The results showed that, within the given parameter ranges, heating temperature, holding time, and quenching time had relatively pronounced effects on the mean residual stress; the mean residual stress was relatively low when the heating temperature was 680 °C, the holding time was 3 s, and the quenching time was 12 s. Heating temperature, quenching air velocity, and quenching time had relatively pronounced effects on the mean springback displacement; the mean springback displacement was relatively low when the heating temperature was 677.5 °C, the quenching air velocity was 13 m/s, and the quenching time was 10 s. Based on the orthogonal analysis, regression models for the mean residual stress and mean springback displacement were further developed, and parameter combinations were screened using the NSGA-III method. Experimental validation showed that the relative error of the mean residual stress was controlled within 15%, indicating that the established model could, to some extent, capture the relationship between process parameters and forming quality indicators, thereby providing guidance for precision forming and process optimization of large-scale thin-walled automotive panoramic roofs. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

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18 pages, 8437 KB

Open AccessArticle

A First-Principles Study of Formaldehyde Adsorption on the Surface of ZnO

[20 \bar{2} 1]

High Index Polar Facet

by Chao Ma, Jingze Yao, Xuefeng Xiao, Yujie He and Hao Zhang

Materials 2026, 19(12), 2661; https://doi.org/10.3390/ma19122661 (registering DOI) - 20 Jun 2026

Abstract

High-sensitivity detection of formaldehyde is critically important for environmental protection and public health. Zinc oxide (ZnO) is a widely used core material for chemiresistive gas sensors; however, its conventional low-index facets suffer from a limited number of active sites, creating a bottleneck for [...] Read more.

High-sensitivity detection of formaldehyde is critically important for environmental protection and public health. Zinc oxide (ZnO) is a widely used core material for chemiresistive gas sensors; however, its conventional low-index facets suffer from a limited number of active sites, creating a bottleneck for further sensitivity enhancement. To overcome this limitation, this study pioneers the application of the highly reactive ZnO

[20 \bar{2} 1]

high-index polar surface for formaldehyde detection. By leveraging its unique stepped atomic configuration and unprecedented density of coordination-unsaturated active sites, we systematically investigate the formaldehyde adsorption behavior and the underlying sensing mechanism using first-principles calculations based on density functional theory (DFT). The pristine ZnO

[20 \bar{2} 1]

surface exhibits intrinsic metallic character. At a coverage of 1 monolayer (ML), the most stable G1 configuration achieves an adsorption energy of −1.54 eV per CH₂O molecule. Within a 2 × 1 supercell, formaldehyde adopts both associative and dissociative adsorption modes. At a lower coverage, formaldehyde forms a stable bidentate structure through dual C–O and Zn–O bonding interactions. Electronic structure analysis reveals significant orbital hybridization and interfacial charge redistribution upon adsorption. Notably, associative adsorption opens a bandgap of 0.04 eV at the Fermi level, inducing a metal-to-semiconductor transition. In contrast, dissociative adsorption results in pronounced n-type doping, thereby elucidating the microscopic origin of the resistivity decrease observed in ZnO-based sensors. Overall, this work highlights the structural advantages of high-index facets and demonstrates for the first time the superior formaldehyde adsorption capability of the ZnO

[20 \bar{2} 1]

facet, providing robust theoretical guidance for the rational design of next-generation, high-performance gas-sensing materials. Full article

(This article belongs to the Section Materials Simulation and Design)

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22 pages, 13504 KB

Open AccessArticle

Optimization of Mixture Parameters for Rubber-Modified Permeable Concrete Bricks Using Response Surface Methodology

by Jiaxiong Zhan, Wei Qiao, Yiran Qin, Zhihua Luo, Haoxian Shi and Jing Li

Materials 2026, 19(12), 2660; https://doi.org/10.3390/ma19122660 (registering DOI) - 20 Jun 2026

Abstract

Permeable concrete bricks incorporating waste tire rubber particles were prepared to improve sustainability and optimize the balance between mechanical performance and hydraulic behavior. Orthogonal experiments and response surface methodology were used to investigate the effects of aggregate-to-binder ratio (A/B), water-to-binder ratio (W/B), rubber [...] Read more.

Permeable concrete bricks incorporating waste tire rubber particles were prepared to improve sustainability and optimize the balance between mechanical performance and hydraulic behavior. Orthogonal experiments and response surface methodology were used to investigate the effects of aggregate-to-binder ratio (A/B), water-to-binder ratio (W/B), rubber content, and rubber particle size on compressive strength and permeability coefficient. Results showed that rubber content dominated compressive strength, while A/B ratio had the greatest influence on permeability. Compressive strength decreased continuously with increasing rubber content and A/B ratio, whereas permeability increased with A/B ratio and showed non-monotonic responses to rubber content and particle size. Response surface optimization identified an optimum mixture: A/B = 3.006, W/B = 0.45, rubber content = 0.103, and rubber particle size = 0.525 mm, yielding a compressive strength of 18.97 MPa and a permeability coefficient of 1.82 mm/s. Validation tests showed relative errors of 1.32% for compressive strength and 3.85% for the permeability coefficient, respectively. SEM and CT analyses revealed that the performance of the permeable concrete bricks was governed by the balance among skeleton integrity, interfacial bonding, and pore connectivity. These findings support the valorization of waste tire rubber in sustainable permeable paving materials. Full article

(This article belongs to the Section Construction and Building Materials)

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16 pages, 3750 KB

Open AccessArticle

Dynamic Magnetostatic Energy Correction Based on Domain Area Evolution for Mesoscopic Hysteresis Modeling

by Mengxing Li, Yao Ying, Jing Yu, Jingwu Zheng, Juan Li, Liang Qiao, Akihisa Inoue and Shenglei Che

Materials 2026, 19(12), 2659; https://doi.org/10.3390/ma19122659 (registering DOI) - 20 Jun 2026

Abstract

In mesoscopic domain energy models of electrical steel sheets, the demagnetizing field H_d is usually held constant at its domain-wall-complete value throughout magnetization. This treatment overestimates the magnetostatic energy at intermediate states and distorts the simulated hysteresis loop. We introduce a field-dependent [...] Read more.

In mesoscopic domain energy models of electrical steel sheets, the demagnetizing field H_d is usually held constant at its domain-wall-complete value throughout magnetization. This treatment overestimates the magnetostatic energy at intermediate states and distorts the simulated hysteresis loop. We introduce a field-dependent coefficient υ_H that scales the magnetostatic energy at each field step. The coefficient is calculated from the aligned-domain area measured by magneto-optical Kerr microscopy and is anchored at the negative coercivity point H = −H_c, where the macroscopic magnetization vanishes and the aligned-domain area S₀ is minimal. The definition follows from the linear relation H_d ≈ N_d·M that holds during domain-wall motion. Measurements in two observation zones of a grain-oriented steel give consistent υ_H curves, confirming the repeatability of the method. When the correction is incorporated into an Assembly Domain Structure Model, the coercivity error drops from 113% to 9–22% relative to the experimental average, with the predicted value falling inside the experimental range, and the remanence error drops from 39.9% to 15–17%. The same correction, applied to a second grain-oriented steel of a different grade, likewise reduces the coercivity and remanence errors (to about 23% and 18%, respectively), confirming that the method is applicable across grades. Full article

(This article belongs to the Special Issue Advances in Characterization, Modeling and Design of Magnetic Materials)

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29 pages, 6878 KB

Open AccessArticle

Stability Prediction of Multi-Factor Coupled Cast Iron Milling System Based on an Improved Full-Discretization Method

by Han Zhang, Minghui Li and Yan Xia

Materials 2026, 19(12), 2658; https://doi.org/10.3390/ma19122658 (registering DOI) - 20 Jun 2026

Abstract

Cast iron components are indispensable in aerospace and automotive systems, yet their milling operations are severely affected by regenerative chatter, which degrades machining quality and damages equipment. Although various chatter prediction methods have been reported, the optimal interpolation strategy of full-discretization methods (FDMs) [...] Read more.

Cast iron components are indispensable in aerospace and automotive systems, yet their milling operations are severely affected by regenerative chatter, which degrades machining quality and damages equipment. Although various chatter prediction methods have been reported, the optimal interpolation strategy of full-discretization methods (FDMs) for multi-factor coupled dynamic systems remains unclear. This study proposes an enhanced FDM to fill this research gap. A dynamic milling model accounting for regenerative effects, modal coupling and process damping is established, and an improved FDM based on Lagrange interpolation is further developed. A systematic single-factor analysis is carried out to examine the performance of 1st–4th-order interpolation for state, delay and periodic terms. Counter-intuitively, convergence analysis and stability lobe diagram (SLD) verification reveal that higher-order interpolation does not guarantee better performance. The optimal orders are identified as 2nd/3rd for state terms, 3rd for delay terms and 1st for periodic terms. Accordingly, the proposed 321-FDM (3rd-order state, 2nd-order delay, 1st-order periodic) exhibits higher accuracy and computational efficiency compared with benchmark methods, namely the semi-discretization method and Hermite-based 3rd-order FDM. Milling experiments on cast iron workpieces validate the established model and the 321-FDM, and the experimental stability thresholds agree well with numerical predictions. This work presents a validated, high-performance stability prediction tool for chatter avoidance in cast iron machining. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

14 pages, 1595 KB

Open AccessFeature PaperArticle

Depth of Cure of a Simplified Bulk-Fill Universal Composite and a Conventional Resin-Based Composite

by Alexis Maquère, Darien DeWolf, Daniel Labrie and Richard B. Price

Materials 2026, 19(12), 2657; https://doi.org/10.3390/ma19122657 (registering DOI) - 20 Jun 2026

Abstract

Objectives: This study evaluated the influence of shade, irradiance, and exposure time on the depth of cure (DoC) of a simplified bulk-fill universal composite (Tetric plus Fill) and a conventional composite (Filtek Supreme Ultra). Methods: The 80% bottom-to-top hardness ratio was used as [...] Read more.

Objectives: This study evaluated the influence of shade, irradiance, and exposure time on the depth of cure (DoC) of a simplified bulk-fill universal composite (Tetric plus Fill) and a conventional composite (Filtek Supreme Ultra). Methods: The 80% bottom-to-top hardness ratio was used as an empirical cutoff, and 99% confidence intervals were calculated using R version 4.5.1. Results: The DoC values were material and protocol dependent. Tetric plus Fill reached the 80% threshold to depths ranging from 3.5 to 4.5 mm, depending on shade and exposure protocol. All the Tetric plus Fill and the Filtek Supreme Ultra products reached their manufacturer’s claimed DoC depth with both 3 s extra-high and 10 s high exposures from the Bluephase PowerCure. Significance: This study highlights the importance of following the manufacturers’ recommendations for increment thickness and exposure time and of recognizing that shade and material formulation influence DoC. Full article

(This article belongs to the Special Issue Recent Research in Restorative Dental Materials (2nd Edition))

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44 pages, 7090 KB

Open AccessArticle

Influence of Polarization Temperature and Time on the Electromechanical Performance of Commercial PZT-4 Ceramics

by Bruna Karina da Silva Oliveira, Douglas Santos Silva, Raí Felipe Pereira Junio, João Gabriel Passos Rodrigues, Rubens Lincoln Santana Blazutti Marçal, Sergio Neves Monteiro, Priscila Simões Teixeira Amaral, Roberto da Costa Lima and Foluke Salgado de Assis

Materials 2026, 19(12), 2656; https://doi.org/10.3390/ma19122656 (registering DOI) - 20 Jun 2026

Abstract

Commercial lead zirconate titanate (PZT) ceramics are widely employed in electromechanical devices due to their excellent piezoelectric response and operational stability. This study investigates the influence of polarization temperature and time on the electromechanical performance of commercial Sparkler PZT-4 (Navy Type I) ceramics. [...] Read more.

Commercial lead zirconate titanate (PZT) ceramics are widely employed in electromechanical devices due to their excellent piezoelectric response and operational stability. This study investigates the influence of polarization temperature and time on the electromechanical performance of commercial Sparkler PZT-4 (Navy Type I) ceramics. Samples were compacted, sintered at 1230 °C, and polarized under temperatures ranging from 80 to 110 °C for 2, 8, and 15 min using a constant electric field of 3.0 kV/mm. Microstructural, physical, and crystallographic analyses confirmed the successful processing of the ceramics, yielding an apparent density of 7.68 g/cm³, relative density of 96.02%, and the predominance of the tetragonal Pb(Zr,Ti)O₃ perovskite phase. Electromechanical characterization revealed a strong dependence of the piezoelectric coefficient (d₃₃) and electromechanical coupling factor (K_p) on the polarization conditions. Maximum values of d₃₃ = 325.8 pC/N and K_p = 0.509 were obtained under elevated temperatures and longer polarization times. A phenomenological Avrami approach indicated faster apparent domain alignment at higher temperatures, while ANOVA and Tukey tests confirmed the significant influence of polarization parameters on the electromechanical response. The results identify favorable polarization conditions for commercial PZT-4 ceramics used in sensors, actuators, and ultrasonic transducers. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

27 pages, 16838 KB

Open AccessReview

High-Entropy Alloys: A Review of Emerging Sensing Materials for Next-Generation Flexible Electronics

by Huatan Chen, Zhongyi Yu, Yang Huang, Bofeng Li, Fangting Feng, Yuming Jiang, Yuting Duan, Gaofeng Zheng and Zungui Shao

Materials 2026, 19(12), 2655; https://doi.org/10.3390/ma19122655 (registering DOI) - 20 Jun 2026

Abstract

High-entropy alloys (HEAs), composed of five or more principal elements in near-equimolar ratios, have emerged as a groundbreaking class of materials for next-generation flexible electronics. This review systematically examines the unique potential of HEAs as sensing materials, moving beyond their traditional role as [...] Read more.

High-entropy alloys (HEAs), composed of five or more principal elements in near-equimolar ratios, have emerged as a groundbreaking class of materials for next-generation flexible electronics. This review systematically examines the unique potential of HEAs as sensing materials, moving beyond their traditional role as structural components. We first elucidate the fundamental mechanisms—core effects including lattice distortion, sluggish diffusion, and the cocktail effect—that endow HEAs with an exceptional synergy of high strength, good ductility, tunable electrical resistivity, and superior electrocatalytic activity. Subsequently, we critically analyze the state-of-the-art strategies for processing HEA-based micro/nano structures, including mechanical alloying, wet-chemical synthesis, and non-equilibrium deposition techniques, with an emphasis on their compatibility with flexible substrates. The core of the review categorizes and discusses the latest advances in HEA-based flexible sensors for strain/stress, gas, and electrochemical (e.g., glucose, biomarkers, heavy metals) detection, highlighting the structure–property–performance relationships. Representative studies have demonstrated that HEA flexible strain sensors achieve a temperature coefficient of resistance as low as 45.59 ppm/K with no signal drift over 6000 stretching cycles; room-temperature hydrogen sensors reach a detection limit down to 31 ppb with a response time of 19 s; and non-enzymatic glucose sensors deliver a sensitivity up to 3043 μA·mM⁻¹·cm⁻². Finally, we summarize the key challenges—such as manufacturing scalability, long-term stability under dynamic deformation, and cost-effectiveness—and provide a forward-looking perspective on promising research directions, including high-throughput compositional screening, multi-functional sensor arrays, and the integration of machine learning for rational material design. Full article

(This article belongs to the Section Metals and Alloys)

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20 pages, 23493 KB

Open AccessArticle

Mechanical Behavior and Damage Characteristics of Cemented Tailings Backfill Under Multiple Different Stress Disturbances

by Xiaofei Li, Yuanfan Liu, Jie Wang, Yan Li and Jianxin Fu

Materials 2026, 19(12), 2654; https://doi.org/10.3390/ma19122654 (registering DOI) - 20 Jun 2026

Abstract

To investigate the impact of underground multiple stress disturbances on the long-term stability of cemented tailings backfill (CTB), this study conducted experiments under different disturbance levels (20–80% of static strength) and frequencies (1–4 times). By comprehensively utilizing mechanical testing, wave velocity monitoring, digital [...] Read more.

To investigate the impact of underground multiple stress disturbances on the long-term stability of cemented tailings backfill (CTB), this study conducted experiments under different disturbance levels (20–80% of static strength) and frequencies (1–4 times). By comprehensively utilizing mechanical testing, wave velocity monitoring, digital image correlation (DIC), and scanning electron microscopy (SEM), the “heterogeneous” evolution mechanism of macro-micro damage was revealed. The results indicate that disturbance level and frequency exert distinctly different driving effects on the deterioration of CTB, rather than a simple linear superposition. Specifically, low-frequency disturbance produces a compaction strengthening effect, microscopically promoting the generation of Ca(OH)₂ and ettringite (increased Ca/Si ratio). In contrast, the combination of high disturbance and high frequency induces free water extrusion and inhibits hydration, leading to an advanced damage threshold based on energy evolution and the accelerated coalescence of microcracks, which favors the formation of C-S-H gel (decreased Ca/Si ratio). Within this heterogeneous mechanism, the disturbance level acts as the dominant controlling factor. This study clarifies the nonlinear mechanical and chemical evolution paths under composite disturbances, providing theoretical support for the dynamic stability control of backfill in deep multi-step mining. Full article

(This article belongs to the Special Issue Advanced Experimental Technology, Theory and Numerical Methods in Concrete Materials)

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19 pages, 21147 KB

Open AccessArticle

Comparative Evaluation of Mechanical Behaviour and Machinability of WAAM-Fabricated Aluminium Alloys

by Saravanamurugan Sundaram, Thenarasu Mohanavelu, Sumesh Arangot, Jana Petru, Mohan Ruthramoorthy, Rashaad Sabir Rowther and Kamalesh Senthilkumar

Materials 2026, 19(12), 2653; https://doi.org/10.3390/ma19122653 (registering DOI) - 20 Jun 2026

Abstract

This study presents an integrated evaluation of the mechanical properties and machinability of thin-walled aluminium alloys fabricated via Wire Arc Additive Manufacturing (WAAM), comparing them against conventional wrought counterparts. Experimental investigations were conducted through tensile testing, hardness measurement, surface characterisation, and cutting force [...] Read more.

This study presents an integrated evaluation of the mechanical properties and machinability of thin-walled aluminium alloys fabricated via Wire Arc Additive Manufacturing (WAAM), comparing them against conventional wrought counterparts. Experimental investigations were conducted through tensile testing, hardness measurement, surface characterisation, and cutting force analysis. The results reveal a critical performance trade-off: WAAM specimens demonstrated superior bulk mechanical properties, most notably a 44.36% increase in tensile strength, alongside enhanced elongation despite a marginal reduction in hardness. However, this structural advantage is counterbalanced by a significant machinability penalty. Frequency domain analysis using Power Spectral Density (PSD) revealed that inherent microstructural porosity in WAAM components triggers dynamic instabilities during machining. These irregularities make the material highly susceptible to high-frequency chatter, ultimately resulting in a 46.73% increase in surface roughness. By establishing a direct relationship between fabrication-induced microstructural defects and dynamic machining degradation, these findings emphasise the necessity for defect-aware, optimised hybrid manufacturing strategies to improve the industrial applicability of WAAM-fabricated structures. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metals, Alloys, and Ceramics: Processes, Microstructures, and Properties)

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20 pages, 3157 KB

Open AccessArticle

A Reciprocal Very-Low-Frequency Mechanically Resonant Magnetoelectric Antenna

by Tingyu Deng, Jinlou Gu, Dong Wang and Jie Jiao

Materials 2026, 19(12), 2652; https://doi.org/10.3390/ma19122652 (registering DOI) - 19 Jun 2026

Abstract

This study investigates an IPS-type Metglas/PMN-PT laminated magnetoelectric composite and its feasibility as a reciprocal mechanical magnetoelectric antenna for low-frequency transmission and reception. Finite-element simulations under quasi-static and frequency-domain conditions reveal strong magnetoelectric coupling under an optimal DC bias field, with both the [...] Read more.

This study investigates an IPS-type Metglas/PMN-PT laminated magnetoelectric composite and its feasibility as a reciprocal mechanical magnetoelectric antenna for low-frequency transmission and reception. Finite-element simulations under quasi-static and frequency-domain conditions reveal strong magnetoelectric coupling under an optimal DC bias field, with both the direct magnetoelectric effect (DME) and converse magnetoelectric effect (CME) exhibiting pronounced resonance near 14.5 kHz, governed by the same longitudinal extensional vibration mode. Five IPS samples were fabricated and experimentally characterized. All devices showed resonant frequencies within 14.1–14.5 kHz, peak DME coefficients of 3.0 × 10⁶ to 3.9 × 10⁶ pC/Oe, and peak CME coefficients of 12.0~15.8 Oe·cm/V, confirming good fabrication consistency, transmit–receive reciprocity, and array-integration potential. The parallel IPS antenna generated a magnetic flux density of 37 nT at 1 m, and exhibited an equivalent magnetic noise of 63 fT/Hz^1/2 at 14.45 kHz. These results demonstrate that the proposed IPS structure combines high-sensitivity reception with efficient low-frequency transmission, showing strong potential for miniaturized, low-power, and long-range magnetic communication and underwater communication applications. Full article

(This article belongs to the Section Materials Physics)

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18 pages, 5389 KB

Open AccessArticle

Synergistic Regulation of Composition and Growth Kinetics in Cobalt-Doped Nickel Sulfides for High-Performance Pseudocapacitors

by Hung Nguyen Dinh, Cu Dang Van, Thu Thuy Luong Thi and Khu Le Van

Materials 2026, 19(12), 2651; https://doi.org/10.3390/ma19122651 (registering DOI) - 19 Jun 2026

Abstract

Transition-metal sulfides are promising electrode materials for high-performance supercapacitors but are often limited by poor conductivity, particle agglomeration, and insufficient active sites. Herein, Co-doped NiS₂ with tunable sulfur vacancies was directly grown on flexible carbon cloth via a facile one-step solvothermal method [...] Read more.

Transition-metal sulfides are promising electrode materials for high-performance supercapacitors but are often limited by poor conductivity, particle agglomeration, and insufficient active sites. Herein, Co-doped NiS₂ with tunable sulfur vacancies was directly grown on flexible carbon cloth via a facile one-step solvothermal method by systematically controlling sulfur source ratio, Ni:Co ratio, temperature, and reaction time. Structural analyses reveal that the optimized conditions of S:(Ni + Co) = 3:1, Ni:Co = 2:1, 160 °C, and 15 h promote the formation of phase-pure Co-doped NiS₂ hierarchical microspheres with enhanced crystallinity and abundant active sites from the synergistic interaction between Ni and Co. Consequently, the optimized electrode delivers an impressive capacitance of 1296 F g⁻¹ at a current density of 1 A g⁻¹, along with excellent rate performance, retaining more than 88% of its capacitance after 1500 charge/discharge cycles at current densities ranging from 2 to 20 A g⁻¹. This work highlights the critical role of synthesis parameter engineering in regulating defect chemistry, structure, and electrochemical performance in advanced energy storage applications. Full article

(This article belongs to the Section Materials Chemistry)

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16 pages, 2215 KB

Open AccessArticle

Effective Elastic Modulus and Strengthening Mechanisms of CNT/Epoxy Composites: A Combined Theoretical and Experimental Study

by Yalei Wang, Jianqiu Zhou, Xiaohan Liu and Leilei Ding

Materials 2026, 19(12), 2650; https://doi.org/10.3390/ma19122650 (registering DOI) - 19 Jun 2026

Abstract

Carbon nanotube (CNT)-reinforced composites are promising advanced materials due to their exceptional mechanical properties. This paper presents a comprehensive investigation of the mechanical behavior of CNT/epoxy composites through theoretical modeling and experimental validation. An equivalent cylindrical fiber model was developed to transform CNTs [...] Read more.

Carbon nanotube (CNT)-reinforced composites are promising advanced materials due to their exceptional mechanical properties. This paper presents a comprehensive investigation of the mechanical behavior of CNT/epoxy composites through theoretical modeling and experimental validation. An equivalent cylindrical fiber model was developed to transform CNTs into effective reinforcement phases, enabling the application of classical composite mechanics. Three reinforcement configurations were analyzed: two unidirectional short fiber models (aligned and staggered) and a three-dimensional four-directional braided long-fiber model. The effects of geometric parameters, including the diameter-to-thickness ratio (D/t) and fiber aspect ratio, on the effective elastic moduli were systematically evaluated. Static and dynamic compression experiments were conducted using an MTS 810 testing system and a Split Hopkinson Pressure Bar (SHPB) to examine the influence of loading rate, vacuum treatment, and reinforcement type (CNT, SiC, and hybrid SiC/CNT) on composite strength. The results indicated that 3 wt% CNT reinforcement increases the Young’s modulus by 30% under static loading and enhanced the dynamic compressive strength under impact loading. The vacuum degassing process significantly affected composite quality, with insufficient vacuum leading to strength degradation due to void formation. Theoretical predictions using Mori–Tanaka and dilute methods showed good agreement with experimental results at low reinforcement volume fractions. Scanning electron microscopy revealed uniform CNT dispersion and provided insights into failure mechanisms, including CNT pull-out and breakage. This work contributes to the understanding of structure–property relationships in CNT-reinforced polymer composites and provides guidelines for achieving their optimal design. Full article

(This article belongs to the Special Issue Mechanical Behavior of Advanced Composite Materials and Structures (2nd Edition))

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