Search Results (431)

Precast reinforced concrete (RC) large-panel buildings (LPBs) are a common residential construction typology in urban areas of Eastern European countries, including Albania. Due to the ageing of these buildings, which date back to the 1970s, and the country’s high seismic hazard, it is very important to assess their seismic safety. This study presents a code-based seismic assessment of a five-storey case-study building in Tirana, Albania’s capital, for which limited information was available and was solely based on the original construction specifications (due to the absence of in situ material testing). A 3D finite-element numerical model was developed using LIRA-SAPR 2024 R2 (version 24.2.0.0) software, and seismic analyses were performed using both multi-modal (response spectra) analysis and the equivalent static analysis procedures according to the current Albanian seismic design code (KTP-N.2-89) and the Eurocode 8 framework (including EN 1998-1 and EN 1998-3). Two different seismic hazard levels were considered to assess the effect of a significantly higher seismic hazard level (compared to the original design) on the seismic safety of older existing LPBs. A demand-to-capacity (DCR) assessment revealed significant structural deficiencies, at both the individual wall-panel level and the wall-assembly level. The representative interior load-bearing wall panel has inadequate flexural and shear capacity, with a DCR of 5.13 for flexure due to a very low vertical reinforcement ratio. The assessment also indicates that the vertical panel joint (D4) is the most critical component of the investigated wall assembly, since its shear capacity is governed by the tensile failure of the steel plate that connects the adjacent wall panels, corresponding to a DCR value of 13.89, indicating very high seismic vulnerability. The seismic assessment of the investigated case-study building may be useful for informing future efforts related to seismic assessment and retrofitting of similar LPBs in Albania and Eastern European countries. Full article

Cryogenic forming overcomes room-temperature limitations by leveraging the enhanced strength–ductility synergy in Al alloys. To explore the forming limits of AA5052 sheet under cryogenic forming conditions, quasi-in situ tensile tests were conducted and digital image correlation techniques were employed to examine strain distribution, surface roughness evolution, and forming limit curves of the AA5052 sheet in the tensile deformation process. Experimental results show that the maximum equivalent forming limit at −196 °C increases to 50.7% from 19.9% at room temperature, representing a 250% increase. At the same time, the surface roughness evolution rate increases by 60% from 2713 nm at room temperature to 4414 nm at −196 °C. Cryogenic conditions suppress dislocation annihilation and dynamic recovery, enhancing strain hardening, resulting in higher forming limits. Additionally, intensified grain rotation and more dislocation slip accelerate surface roughening, which influences the development of the geometric heterogeneity coefficient. By introducing a strain-dependent surface roughening coefficient, the Marciniak–Kuczyński (M-K) model was modified and was used to quantitatively characterize the heterogeneity during deformation, and subsequently analyzes its impact on the prediction of forming limits for AA5052 from room temperature (25 °C) to cryogenic temperature (−196 °C). The modified model reduces the prediction standard deviation by more than 70% and the identified mechanisms offer theoretical guidance for optimizing cryogenic forming process parameters for Al alloy components with complex geometries. Full article

Thin spray-on liner (TSL) technology provides rapid and highly automated surface support for underground coal mine roadways. However, in deep roadways affected by high in situ stress, mining-induced disturbances, and fractured surrounding rock, conventional TSL materials require improved tensile–shear resistance, deformation compatibility, and support adaptability. Although fiber reinforcement is an effective method for enhancing polymer composites, systematic studies on the effects of fiber type and dosage in reactive polymer-based TSL materials remain limited. In this study, a commercially available two-component polyurea-silicate-based TSL matrix was reinforced with polyvinyl alcohol (PVA) fibers, polypropylene mesh fibers, and toughened polypropylene fibers at volume fractions of 0.25–1.50%. A stepwise experimental program, including uniaxial compression, variable-angle shear, tensile, circular-indenter buffered shear, and true triaxial tests, was conducted to evaluate the mechanical behavior and support-related performance of the fiber-reinforced TSL materials. The basic mechanical tests showed that the 0.75% toughened polypropylene fiber group maintained favorable compressive and shear resistance, achieving a cohesion of 8.65 MPa and an internal friction angle of 24.12°. PVA fibers exhibited higher tensile reinforcement efficiency at relatively low contents, with the 0.25% PVA fiber group reaching a peak tensile stress of 13.61 ± 1.00 MPa. The 1.0% PVA fiber group showed good deformation coordination, with a compressive strength of approximately 49.87 MPa. In the circular-indenter buffered shear test, the 1.0% PVA fiber group reached a peak load of 0.636 ± 0.055 kN and an absorbed energy of 3.118 ± 0.832 J at 10 mm displacement. Under true triaxial loading, the 1.0% PVA fiber group absorbed 311.4 J of energy at a displacement of 10 mm, approximately 5.5% higher than that of the 0.75% toughened polypropylene fiber group. Therefore, 1.0% PVA fiber reinforcement is recommended as the optimal reinforcement scheme for polymer-based TSL materials used in deep, fractured, and large-deformation coal mine roadways. Full article

Temperature- and strain-rate-dependent serrated flow, localized plastic instability, and qualitative microcrack evolution in Mn13 Hadfield steel were investigated using stress–strain analysis and in situ tensile observation. Solution treatment at 1050 °C for 1–1.5 h followed by water quenching yielded homogeneous single-phase austenite. Type A and Type B serrations were dominant at room temperature at 1 × 10⁻³ s⁻¹ and at 100 °C at 1 × 10⁻² s⁻¹, whereas the room-temperature specimen tested at 1 × 10⁻² s⁻¹ showed delayed serration onset and pronounced Type B stress drops only at high strains. Type C serrations occurred mainly near fracture at 100 °C at 1 × 10⁻³ s⁻¹, 200 °C at 1 × 10⁻² s⁻¹ and 200 °C at 5 × 10⁻² s⁻¹. In situ observations further reveal that different serration types correspond to distinct localized deformation modes. During Type A serrations, the tracked feature exhibited unidirectional stepwise migration involving forward motion, arrest, and renewed advance. Type B serrations were associated with discontinuous pulse-like migration characterized by rapid forward motion, brief arrest, local backward motion, and renewed advance. No regular trajectory was observed during Type C stress drops; only local brightness changes and slight positional shifts occurred. These observations link macroscopic serrations to localized deformation in Mn13 steel and provide qualitative in situ evidence for grain-boundary microcrack initiation and evolution during deformation. Full article

This work describes the design and characterization of nanocomposites based on multi-walled carbon nanotubes (MWCNTs) and commercial polymer matrices for innovative electronic applications. This work addresses the need for advanced materials for flexible electronics, sensing, and electromagnetic shielding. Sipolprene^® 25170-W, a flexible and durable polyester–polyether block copolymer, was used as the matrix. For filler incorporation, the commercial masterbatch Plasticyl™ PBT-1501 (15 wt% of MWCNTs in PBT, polybutylene terephthalate) was employed, ensuring operational safety and ease of dispersion. The samples were produced as films (with masterbatch contents ranging from 10% to 30% corresponding to a MWCNT content ranging from 1.5 wt% to 4.5 wt%) via twin-screw extrusion with a flat die. Characterization included SEM, FT-IR, TGA, DSC, tensile testing, surface wettability, volume resistivity measurements, and electro-mechanical tests. All the results confirmed good dispersion of the filler within the matrix: from a mechanical point of view, the addition of MWCNTs increased the Young’s modulus from 25 MPa of the neat material to 122 MPa of the material containing 4.5 wt% of MWCNTs, enhancing stiffness while maintaining good film handleability. Thermal analysis revealed the high stability of the obtained system and allowed us to identify the appropriate processing temperature parameters to guarantee the thermal stability of the materials during processing. Finally, electrical tests demonstrated a significant reduction in volume resistivity with increasing filler content: the volume resistivity decreased by about eleven orders of magnitude, from approximately 10⁸ Ohm × cm of the unmodified material to 10⁻³ Ohm × cm for the material containing 4.5 wt% of MWCNTs. the sample with 30% of filler exhibited the typical behavior of a conductive material, and it was demonstrated that it could be used as an in situ strain sensor. All these findings confirm the potential of the developed materials for advanced technological applications. Full article

Sudden rupture of freezing pipes frequently occurs in artificial ground freezing engineering. Owing to complex field environments, it is difficult to clarify the single-factor evolutionary laws of vibration signals induced by pipe fracture through field monitoring. Four groups of model freezing pipes with diameter-to-thickness ratios ranging from 20 to 26 were fabricated through geometric scaling based on engineering prototype pipes of Φ140 × (5–7) and Φ159 × (6–8). A low-temperature brine medium at −30 °C was circulated inside the pipes to simulate actual in situ refrigeration conditions. A series of tensile rupture tests were performed to explore the vibration response characteristics of freezing pipes with different specifications. The test results indicate that the ultimate rupture load is positively correlated with signal energy. Within the diameter-to-thickness ratio range of 20–26, the signal amplitude decreases approximately linearly (R² = 0.99), while the progress count and signal energy increase gradually, and the dominant frequency of rupture vibration signals decreases continuously. In other words, the dominant frequency gradually declines as the diameter-to-thickness ratio rises. Unlike conventional acoustic emission characteristics of bare steel fracture, which are typically characterized by high-amplitude, high-energy bursts with prominent central frequencies, the vibration signals of freezing pipes surrounded by frozen soil exhibit significantly lower dominant frequencies (3–30 kHz), rapid attenuation due to pipe–soil energy radiation, and a frequency shift that is structurally governed by the diameter-to-thickness ratio rather than by material properties alone. The quantitatively established frequency bands and parameter evolution patterns can serve as reference criteria for field monitoring and early warning of freezing pipe fracture in artificial ground freezing engineering. Full article

Handling hydrogen-rich atmospheres requires materials that do not deteriorate in the presence of hydrogen and that ensure safe operation. Often high strength metallic materials, however, may show catastrophic mechanical failure in the presence of hydrogen. This phenomenon, called hydrogen embrittlement, can be very dangerous, as these failures occur in a time-delayed and sudden manner. Two commercially available materials, AMPCOLOY^® 83, a copper beryllium alloy, and AMPCO^® 18, an aluminum bronze, have been investigated to clarify their susceptibility to hydrogen embrittlement. Hydrogen permeation measurements were performed to assess diffusivity in the materials, and hydrogen content was analyzed by thermal desorption analysis (TDA) after electrochemical charging. Mechanical properties in hydrogen-affected state were assessed by slow strain rate tensile tests (SSRT), with in situ electrochemical charging and post-test fractographic inspection of the fracture surfaces. While the aluminum bronze showed no noticeable hydrogen-related deterioration, copper beryllium alloy experienced some embrittlement, however, having a low fracture strain even in the uncharged state. Full article

Bamboo is a natural fiber-reinforced composite whose macroscopic mechanical properties depend on the microscale synergistic deformation of fibers and parenchyma. However, existing in situ SEM testing techniques are mainly designed for metallic tensile testing and are unsuitable for analyzing bamboo’s meso-scale behavior. To address this, we developed an in situ SEM three-point bending instrument specifically for natural fiber materials. The instrument keeps the region of interest (ROI) stably centered in the SEM field of view through a stationary central indenter and symmetrically moving supports. It offers a 0–450 N load range, 0.5N force resolution, 1 μm displacement resolution, and is compatible with a Tescan Vega 4 SEM chamber. Using this instrument, in situ bending tests were performed on Moso bamboo (Phyllostachys edulis) with fiber volume fractions of 23%–42%, combined with digital image correlation for full-field strain measurement. Results show that flexural modulus, strength, and fracture work all increase significantly with fiber content. A microstructural failure classification framework was established based on in situ SEM observations, categorizing the observed failure modes according to the local arrangement of fibers and parenchyma. The proportions of these failure modes were found to be closely associated with the gradient distribution of strength and toughness across the culm wall. Three extrinsic toughening mechanisms were identified: fiber-induced crack deflection, parenchyma cell collapse densification, and fiber–parenchyma interfacial debonding. The developed instrument and analysis method offer a promising experimental platform for multi-scale mechanical characterization of natural composites. Full article

Given the urgent need to regulate oxidative stress microenvironments in chronic wound healing, hydrogel dressings that simultaneously integrate antioxidant, antibacterial, mechanically adaptive, and biocompatible properties are highly desirable. In this study, a natural polymer-based composite hydrogel dressing loaded with zinc-quercetin nanozyme (Zn-Q) was designed. The gel skeleton was constructed via a dual network of photocrosslinked methacrylated silk fibroin (SilMA) and mercaptolated hyaluronic acid (HA-SH) via thiol-ene click chemistry, with the catalase (CAT)-like Zn-Q nanozyme encapsulated in situ within the network, thereby achieving synergy between chemical crosslinking and dynamic metal-polyphenol coordination. Systematic characterization revealed that Zn-Q nanozyme adopted a stable octahedral coordination configuration, and its continuous porous structure exposed abundant catalytically active sites. The composite hydrogels exhibited a highly interconnected, three-dimensional (3D) porous morphology, with swelling ratios that increased significantly with Zn-Q nanozyme content (up to around 1082%). Rheological and mechanical tests demonstrated that although incorporating the nanozyme reduced the storage modulus, the reversible physical crosslinks formed via hydrogen bonding and coordination interactions endowed the material with excellent tensile toughness and energy-dissipation capacity, exhibiting typical Mullins softening behavior. Functional evaluation showed that Zn-Q nanozyme conferred superior free radical scavenging capability to the hydrogels and exerted dose-dependent inhibition against both Staphylococcus aureus and Escherichia coli. Furthermore, the hydrogels exhibited favorable adhesion to various wet organs and heterogeneous material surfaces, with hemolysis rates below 5% and cell viability exceeding 100% after 3 days of culturing with fibroblasts, confirming their excellent hemocompatibility and cytocompatibility. This study provides an experimental basis for developing a new type of wound repair materials that integrate antioxidant, anti-infective, and mechanically adaptive properties, holding significant application potential in oxidative stress-related tissue repair fields. Full article

This study presents a laboratory-scale assessment of heat-assisted fly ash-based geopolymer concrete as a potential thin protective layer in one asphalt–geopolymer pavement configuration. The programme comprised water penetration under pressure, abrasion, initial skid resistance, wheel tracking, four-point-bending fatigue, mechanical strength, freeze–thaw response, de-icing-salt scaling, thermal characterization, and qualitative scanning electron microscopy. The selected geopolymer reached mean flexural, compressive, and splitting tensile strengths of 10.756, 61.058, and 3.797 MPa, respectively. Final rut depths were 1.57 mm after 7 days and 0.72 mm after 28 days, with corresponding WTSAIR values of 0.020296 and 0.014238 mm per 10³ cycles. After 10⁶ cycles at 10 Hz, 72–85% of the initial stiffness modulus remained across the tested strain levels. Mean de-icing-salt scaling was 0.500 kg/m² after 28 days and 0.995 kg/m² after 56 days. Standalone geopolymer specimens underwent full-depth water penetration, whereas no leakage through the asphalt layer was observed in the intact layered specimen during the 5 bar, 72 h test. This system-level observation supports functional tightness only under the tested intact condition and does not establish intrinsic material impermeability or long-term interface durability. Interpretation is limited to this laboratory-scale configuration: the 90 °C heat-assisted curing protocol limits transfer to conventional in situ paving; no ambient- or standard-cured control and no same-condition conventional overlay control were included; and only one composite geometry was evaluated. The findings therefore define application boundaries for further validation rather than a field-ready specification or proof of comparative superiority. Full article

The shear characteristics of soil–root systems are dynamic indicators for assessing soil erosion resistance. Vegetation type influences shear characteristics by altering soil properties and root traits. However, the mechanisms by which mixed vegetation roots affect shear characteristics remain unclear. We selected naturally restored forestland (with Dicranopteris dichotoma, Baeckea frutescens, and their combinations) and artificially managed orchard systems (with Paspalum wettsteinii, Gardenia jasminoides, and their combinations) in the erosion-prone red soil region of southern China. In situ shear tests were conducted to explore the shear characteristics of soil–root systems under different vegetation types, identify the main influencing factors, and clarify the underlying mechanisms. Shear fracture energy (SFE), peak shear stress (PSS), and peak shear stress displacement (DPS) decreased with increasing soil depth across all sites. The average SFE and PSS in the forestland were 2.44 and 3.11 times higher, respectively, than those in the orchards. The main factors influencing shear characteristics in forestland included root volume density, tensile strength, bulk density, and mean weight diameter of aggregates (MWD), whereas those at the orchard sites included root length density, tensile strength, and organic matter content. Root factors had a stronger impact on shear fracture energy than soil properties. Shear fracture energy equations were constructed for forestland and orchard sites, showing high R² and Nash–Sutcliffe efficiency values, indicating adequate predictive performance. These findings contribute to our understanding of the mechanical mechanisms of soils under vegetation restoration, provide scientific evidence for soil and water conservation evaluations, and help optimize vegetation restoration strategies in the Southern Red Soil Region. Full article

Lightweight polylactic acid (PLA LW) is a thermally activated foaming filament in which print temperature governs the extent of in situ gas expansion. This dual role, as a microstructural design parameter and a primary source of performance variability, motivates the three-phase, multi-factorial experimental program reported here. FDM-printed specimens of three infill topologies were investigated: orthogonal Cubic, hierarchical Subdivision Cubic (Sub-Cubic), and Gyroid triply periodic minimal surface (TPMS), each representing a distinct crystallographic symmetry class. A total of 504 specimens were fabricated across eight print temperatures (190–260 °C), three flow rate settings (70%, 80%, 100%), and four infill ratios (10%, 20%, 40%, 60%) and tested under quasi-static tensile and Charpy impact loading, with six replicates per condition distributed across two independent batches. One-way ANOVA confirmed a strong temperature effect on ultimate tensile strength (UTS) in Phase 1 (F(7,40) = 22.37, p < 0.001), while the Gyroid is uniquely temperature-sensitive in Phase 2 at 70% flow rate (F(1,8) = 14.30, p = 0.005) compared to the Cubic and Sub-Cubic, which exhibit no significant temperature effect in the 230–240 °C window. The Gyroid at 240 °C and 70% flow rate achieved the highest specific strength among Phase 2 configurations (20.9 MPa·cm³/g); Phase 3 demonstrated that Gyroid-specific strength decreases monotonically with the infill ratio, reaching 15.4, 12.3, and 8.8 MPa·cm³/g at 10%, 40%, and 60% infill, respectively. Cubic infill at 230 °C and 80% flow rate delivered the most reproducible performance (CV_UTS = 3.3%), while Sub-Cubic at the same condition combined high specific strength (20.5 MPa·cm³/g) with low variability (CV_UTS = 4.3%); both observations are quantified through a symmetry robustness index and a symmetry consistency indicator. Macrographic fractography supported geometry-controlled fracture: Cubic specimens fracture along layer interface mirror planes or ±45° shear planes depending on the thermal regime, while Gyroid specimens exhibit multi-plane, curvature-deflected fracture with no preferred crack propagation direction. These results indicate that geometric symmetry class is an important organizing factor for the mechanical response of FDM-printed PLA LW structures within the investigated parameter space. Full article

The macroscopic mechanical properties of near-β titanium alloys depend inherently on their complex microstructural morphologies and phase transformation kinetics. This study investigates the deformation behavior of a lamellar Ti-55531 alloy during isothermal compression and in situ tensile testing. Pronounced strain rate sensitivity dictates the deformation of the lamellar microstructure. Low strain rate deformation (0.001 s⁻¹) induces dynamic recovery and recrystallization, which in turn drive α-lamellae fragmentation and the nucleation of new α phase during compression. The α precipitation is governed by a strict Burgers orientation relationship (BOR), but extensive plastic deformation may lead to the breakdown of the BOR. During tension, continuous slip transfer between adjacent phases is critically restricted by α/β interfacial thickness. As plastic strain accumulates, lath-like, V-shaped, and acicular α phases precipitate concurrently within β grains, creating a complex α microstructure. Full article

Lithological, metasomatic, and structural heterogeneity in ore-hosting rocks limits the reliability of applying a single set of mechanical parameters without domain subdivision. This study evaluates intact rock properties, shear resistance along natural discontinuities, and conditional upscaling to the rock mass scale. The database comprised 232 laboratory records from 36 geotechnical borehole identifiers: 73 Brazilian tensile tests, 68 uniaxial compression tests, 49 triaxial compression tests, and 42 direct shear tests. Four domains were defined: D1, beresite-altered granodiorites; D2, diorites; D3, granodiorites; and D4, lamprophyre dikes. The lowest mean uniaxial compressive strength occurred in D1 (91.75 ± 40.65 MPa), whereas D2 showed the highest mean value, although its small sample size precludes confirmation as a domain characteristic. D3 provided the most representative dataset and exhibited intra-domain variability, while D4 showed the greatest variability in Young’s modulus (CV = 82.21%). Mean apparent cohesion along natural discontinuities was 0.125 ± 0.039 MPa for D1 and 0.140 ± 0.083 MPa for D3; D2 and D4 remain preliminary. GSI values of 48–58 were used only in scenario-based Hoek–Brown calculations. A ±5-point change in GSI altered equivalent rock mass strength by approximately −25% to −26% and +33% to +34%. The results support domain-based parameterization but require in situ verification. Full article

This study presents the development of a proof of concept, functional hydrogel interface designed for the acquisition of physiological signals, such as electrocardiogram (ECG) and electromyography (EMG). The hydrogel is synthesized using chitosan extracted from the shells of Tenebrio molitor larvae through a sustainable acid–alkaline protocol, blended with glycerol, polyvinyl alcohol (PVA), and ionized with NaCl to enhance conductivity. The resulting hydrogel membranes were cast and cut into circular shapes to provide a uniform contact geometry. The fabrication process yielded flexible membranes exhibiting ionic conductivity and partial surface conformity and handling stability. The extracted chitosan was characterized by Fourier-transform infrared spectroscopy (FTIR), degree of deacetylation (DDA), and molecular weight determination. Mechanical characterization included compression and tensile testing, while electrical characterization was performed through impedance spectroscopy and comparison with a commercial hydrogel interface. Functional evaluation was conducted through ECG and EMG signal acquisition under controlled experimental conditions. Preliminary in situ ECG and EMG recordings demonstrated successful signal acquisition using the proposed hydrogel interface. Future work may further investigate the mechanical and electrical behavior of the hydrogel under broader experimental conditions, as well as the optimization of the hydrogel formulation and extended physiological signal acquisition. Studies may help further characterize its potential as a chitosan-based bio interface material for bioelectrical sensing applications. Full article