Search Results (150)

Dry-connected prefabricated composite walls have been increasingly used in steel structures owing to the development of building industrialization and the demand for rapid and efficient construction. However, the respective influences of dry-connection configuration and wall panel material on the seismic response of prefabricated composite walls require further clarification. To address this issue, full-scale quasi-static tests, continuum damage mechanics (CDM) analysis, and finite element simulations were conducted. Six specimens were tested under low-cycle reversed loading. The influence of connection type was evaluated by comparing MRC walls with U-type and Z-type connections, whereas the influence of wall panel material was evaluated by comparing MRC and SFC walls under U-type connections. For the tested MRC walls, the deformation capacity of the connections strongly influenced the failure mode. The U-type rigid connections provided limited deformation buffering, resulting in stress concentration at the wall ends, initial cracking at displacements of 8–10 mm, rapid crack propagation, and semi-brittle failure. In contrast, the Z-type flexible connections released deformation demand through the slip and rotation mechanisms of the slotted holes. The maximum tested displacements of the Z-type specimens were approximately 2.58–2.78 times the ultimate displacements of the corresponding U-type specimens. The Z-type specimens maintained stable load-carrying behavior with limited panel damage throughout the tested displacement range. Furthermore, a restoring-force calculation method was established based on CDM theory, and the predicted peak loads were generally consistent with the experimental results. This study identifies the load-transfer, deformation, and energy-dissipation characteristics of the tested connection–panel configurations and provides comparative evidence for the further development of prefabricated composite wall systems. Full article

The elastoplastic behaviour and failure of unreinforced masonry structures under biaxial loading are critically governed by the mechanical response of brick–mortar contact interfaces. Detailed finite element micromodelling explicitly resolves these elements, offering rigorous numerical representation; however, practical implementation requires the determination of contact stiffness parameters, for which no established experimentally calibrated expressions exist. This study presents an experimental-numerical calibration methodology integrating experimental characterisation of constituent materials and small-scale masonry specimens with numerical validation, using a concrete damaged plasticity model for quasi-brittle materials and traction-separation laws for interfaces, applied to a specific ceramic masonry system. The proposed methodology provides a practical and reproducible basis for experimental calibration of the contact stiffness parameters required in the detailed micromodelling of brick–mortar interfaces. Numerical simulations reproduce experimental behaviour, with peak load predictions within ±6% for normal and ±1% for shear loading. Detailed micromodelling reveals that normal stresses develop at interfaces even under nominally pure shear, evidencing coupled normal-tangential behaviour, the key role of normal adhesive contact strength, and the justification for the cohesive–frictional interface characterisation. Full article

To enhance the crack resistance and toughness of cement mortar, steel fibers (SF), carbon fibers (CF), and their hybrid combinations were incorporated at various volume fractions. Cubic specimens with single or double prefabricated holes were tested using compressive and splitting tensile tests combined with digital image correlation technology (DIC). to evaluate mechanical properties, crack propagation, and failure patterns. Results indicate that steel fibers primarily suppressed macrocracks via bridging and improved strength, while carbon fibers inhibited microcrack initiation and promoted uniform strain distribution. Hybrid fibers achieved combined reinforcement, with the S2C02 mixture exhibiting the best overall performance: compressive strength increased by 39.7–55.1%, tensile strength by 70.45–75.9%, and the toughness and tensile/compressive ratio were enhanced. DIC analysis showed reduced strain concentration, more uniform strain fields, delayed crack propagation, and a transition from brittle to quasi-ductile failure. These findings demonstrate an optimal hybrid fiber dosage and reveal the combined mechanism of steel–carbon fibers in defect-containing cement mortar, providing guidance for material design and performance optimization. Full article

A new micropolar peridynamic framework incorporating stress- and stretch-based failure criteria was developed for simulating concrete structures. A nonlocal micropolar peridynamic stress tensor was employed to solve plane stress problems; this approach inherently manages cracks and damage. A direct correspondence was established between the classical constitutive stress–strain tensor and the associated micropolar peridynamic stress tensor for linearly elastic materials. Moreover, in contrast to standard peridynamic models that treat the material horizon as a purely abstract parameter, this research defines the horizon based on Poisson’s ratio, material strength, and fracture toughness. In addition, a numerical matrix-based scheme was implemented to model concrete problems using a nonlinear explicit dynamic relaxation solver. To assess the model’s performance, concrete structures under plane stress were examined. The model’s results align closely with the crack paths and experimental data from physical testing and demonstrate mesh independence. The implementation of the model with stress and stretch failure criteria mitigates spurious boundary effects, ensuring spatial convergence. Full article

Triply periodic minimal surface (TPMS) gyroid lattices are promising lightweight and energy-absorbing polymer structures, but their manufacturability by material extrusion (MEX) depends strongly on cell size, grading direction, and relative density. This study investigates PLA gyroid lattices with uniform and graded cell-size configurations using initial and final cell sizes of 1, 1.5, and 2 mm and target relative densities of 10, 20, and 30%. A full-factorial design was used to construct a printability map, followed by quasi-static compression testing, areal surface-roughness characterization, and SEM observation of representative specimens. The printability results showed that low-density fine-cell configurations were most prone to incomplete wall formation and collapse, whereas the 30% relative-density group was printable for all investigated cell-size combinations. Under compression, the 30% relative-density uniform 1 mm gyroid showed the highest maximum stress among the tested configurations, while graded structures terminating in smaller cells also provided favorable load bearing and energy-absorption behavior. The plateau stability index, calculated from stress fluctuations between collapse and densification, helped distinguish stable progressive collapse from more oscillatory deformation. Surface roughness and SEM observations further indicated that smoother, more continuous wall surfaces were associated with more uniform deformation, whereas rougher and defect-rich surfaces promoted localized buckling, cracking, and brittle collapse. Overall, the results identify experimentally supported relationships between gyroid cell-size configuration, printability, surface integrity, and compressive response within the investigated PLA MEX design space. Full article

The modification of cementitious binders using active mineral additives and nano-components represents a crucial pathway for developing high-performance, sustainable concrete composites. Nevertheless, unilateral modification of the matrix with highly reactive siliceous materials often leads to an undesirable increase in composite brittleness. This study investigates the synergistic effect of the concurrent application of nano-silica (NS), silica fume (SF), and Class F fly ash (FA) in ternary and quaternary binders, aimed at optimizing both load-bearing capacity and fracture toughness. The experimental program was conducted on seven concrete series, evaluating their mechanical parameters and non-linear fracture properties using the two-parameter fracture model (TPFM) on notched beams subjected to three-point bending. Additionally, a high-resolution energy partitioning framework was applied, decomposing the total fracture energy into four distinct components—fracture initiation energy in the elastic range (G_ini), pre-peak microcracking energy (G_pre), main material softening energy (G_soft), and residual tail energy dissipated at large crack openings (G_tail)—along with the determination of the characteristic length (l_ch). The results demonstrated that while purely siliceous systems (modified with NS and SF) generate high strength increments, they simultaneously trigger a “brittleness trap,” manifested by a 13.65% decrease in the l_ch parameter. The introduction of FA effectively mitigates this hazard, transforming the failure mode into a quasi-ductile behavior. The concrete series modified with the NS+FA hybrid (Mix-5) exhibited a spectacular 107% increase in G_f and an increase in l_ch of nearly 50%, while maintaining high fracture toughness. Energy decomposition analysis in quaternary concretes confirmed a desirable reduction in the initiation energy share in favor of the softening and tail phases (G_tail reaching a record 13.1% for Mix-7), suggesting the probable activation of macroscopic crack-bridging mechanisms driven by the delayed hydration of FA particles. The research indicates that precise design of multi-component binders allows for achieving an optimal technological equilibrium point—the “sweet spot”—combining high structural capacity with safe material ductility. Full article

Hydraulic fracturing is the primary technology for extracting unconventional oil and gas resources. Rock apparent fracture toughness is the most critical parameter in hydraulic fracturing processes. Rock apparent fracture toughness exhibits characteristics distinct from those of metallic materials, particularly as field-estimated values of rock apparent fracture toughness in hydraulic fracturing exceed laboratory-measured values by 1–2 orders of magnitude. Existing interpretation models assume a constant stress distribution in the fracture process zone (FPZ), which contradicts the softening behavior of rock. To address this gap, and based on the assumption of a power-law softening stress distribution in the FPZ of quasi-brittle rock, we develop a mode I apparent fracture toughness model for rock under far-field tensile and compressive stress configurations. This model considers both the softening characteristics of rock and the fluid lag effect. A comparative analysis was conducted on the differences in rock apparent fracture toughness between far-field compressive stress and tensile stress configurations. The results reveal that the difference in configuration between far-field compressive stress and tensile stress constitutes the fundamental reason for the order-of-magnitude discrepancy between the rock apparent fracture toughness estimated from hydraulic fracturing field tests and that measured in laboratory experiments. The influence of the ratio of in situ stress to tensile strength, the ratio of FPZ length to fracture length, the ratio of fluid lag zone length to fracture length, and stress distribution within the FPZ on rock apparent fracture toughness was analyzed, and these factors are found to have decisive effects on the rock apparent fracture toughness. Additionally, the size effect on rock apparent fracture toughness was discussed. This research contributes to more precise hydraulic fracturing parameter design. Full article

The growing adoption of wire arc additive manufacturing (WAAM) requires an understanding of how WAAM-fabricated aluminium alloys respond to environmental factors that may degrade mechanical performance. This study investigates the effects of cathodic charging on the mechanical properties and fracture behaviour of WAAM AA2319 aluminium alloy. Cathodic charging was conducted in an electrolyte containing 3.5 wt.% NaCl and 3 g/L ammonium thiocyanate using different applied current densities. The resulting changes in mechanical performance were assessed through uniaxial tensile and Charpy impact toughness tests. The results demonstrate that cathodic charging led to a progressive reduction in ductility with increasing current density. Elongation decreased by up to approximately 45% relative to the uncharged condition, while ultimate tensile strength and yield strength were marginally affected. Charpy impact testing revealed a corresponding reduction in impact toughness of approximately 40% following hydrogen charging. Fractographic analysis showed a transition from ductile fracture dominated by microvoid coalescence in the uncharged material, to a mixed ductile–brittle fracture in hydrogen-charged specimens, characterised by shallow dimples and quasi-cleavage features. The observed changes in mechanical behaviour and fracture morphology suggest that cathodic charging promoted hydrogen-assisted mechanical degradation, with features consistent with hydrogen-enhanced localised plasticity (HELP) and hydrogen-enhanced decohesion (HEDE). Full article

Additively manufactured cellular architectures frequently exhibit brittle failure under impact due to layer-induced stress concentrations. Through the programming of architectural and material design, specifically combining Fused Deposition Modeling (FDM) lattice topology with hyperelastic polyurea infiltration, this study achieves active control over the macroscopic transition from catastrophic structural fragmentation to stable progressive collapse. To evaluate this, auxetic and honeycomb specimens printed with ABS and glass-fiber-reinforced polyamide (PA-GF) were evaluated in unreinforced and polyurea-infiltrated states under quasi-static compression, three-point bending, and Charpy impact loading. Results show that the compressive response depends primarily on cellular topology; the pure auxetic (A-A) configuration provided the highest stiffness and energy absorption. Polyurea infiltration did not significantly alter elastic stiffness but increased post-yield stability, leading to a 96.6% elastic recovery in PA-GF A-A structures. In flexure, the base polymer governed stiffness, with ABS structures measuring 68% stiffer than PA-GF. Unreinforced ABS achieved 34% higher specific energy absorption (SEA) than PA-GF under compression, with the A-H topology maximizing SEA. Under dynamic impact, PA-GF absorbed an average of 70% more energy than ABS, and the H-A configuration recorded the highest impact resistance. The addition of polyurea shifted the failure mode from brittle fragmentation to stable elastomeric deformation, increasing absorbed impact energy by 52% for ABS and over 30% for PA-GF, preventing catastrophic structural failure. Integrating topological sequencing with elastomeric confinement provides a direct method to control energy dissipation and damage tolerance in 3D-printed cellular composites. Full article

Rock–concrete composites are critical load-bearing elements in geotechnical engineering applications such as slope support. Their mechanical response and damage evolution after fatigue disturbances, such as blasting and mechanical operations, govern the long-term stability and safety of engineered structures. To fully capture these complex behaviors, this study presents a novel multi-scale approach by integrating uniaxial compression tests with three-dimensional digital image correlation and discrete element modeling. This combined experimental–numerical framework is employed to systematically examine the macro- and meso-scale mechanical behavior, crack evolution, and energy response of composites with varying interface angles after quasi-static cyclic loading. The results reveal that as the interface angle increases, the peak strength declines markedly while the brittleness index increases, reflecting a distinct transition in the failure mode from plastic-dissipation-dominated to elastic-energy-storage-dominated. Consequently, the dominant failure mechanism shifts from tensile to shear-slip control. Furthermore, fatigue disturbances exacerbate material degradation, inducing a composite “interface shear–end tension” failure in specimens with higher interface angles and significantly raising the proportion of shear cracks. Energy analysis indicates that cyclic loading enhances the elastic energy storage capacity, and the energy conversion threshold rises continuously with the interface angle. These findings clarify the multi-scale control mechanisms of interface geometry on fatigue-induced failure, providing a theoretical foundation for predicting fatigue life and enabling early pre-warning of failures in rock–concrete engineering structures. Full article

Accurate prediction of the shear capacity of reinforced concrete (RC) deep beams remains challenging due to the complex interaction of multiple load transfer mechanisms and the pronounced size effect in quasi-brittle materials. Existing strut-and-tie-based models are widely used in practice; however, they often neglect the coupled influence of structural size and longitudinal reinforcement, leading to reduced reliability for large-scale members. In this study, a modified simplified strut-and-tie model (M-SSSTM) is proposed in order to achieve a fracture mechanics-inspired empirical enhancement in shear strength prediction; in the model, a size effect coefficient and a reinforcement-related term accounting for dowel action are explicitly incorporated. The size effect coefficient is calibrated using an extensive database comprising 572 test results collected from the literature, ensuring that the formulation captures the general trend of size-dependent behavior. To verify the predictive capability of the proposed model, nine RC deep-beam specimens were tested, and the comparison between predicted and measured results demonstrates improved accuracy and reduced scatter relative to existing methods. The results indicate that incorporating the coupled effects of size and longitudinal reinforcement is essential to rational shear design, and the proposed model provides a robust and practical tool for the analysis and design of RC deep beams, particularly for large-scale structures. Full article

Additive manufacturing with soil–cement mixtures is emerging as a disruptive approach to advancing sustainable manufacturing processes. However, its industrial scalability remains limited by material brittleness and a lack of process standardization. This study presents an integrative literature review that critically evaluates the influence of fiber reinforcement on the 3D printing process and the mechanical performance of soil–cement mixtures within the context of sustainable construction and circular economy principles. The analysis integrates fresh-state rheological behavior with hardened-state performance, showing that an optimized fiber dosage (0.3–0.5% by volume) shifts the failure mode from brittle to quasi-ductile while reducing crack propagation by approximately 60%. Additionally, the study compares various fiber types, including synthetic and natural alternatives. The results show that synthetic fibers used at low dosages (0.5–1.0% by volume) provide the greatest improvements in tensile strength and post-cracking ductility. In contrast, natural fibers, typically used at higher dosages (8.0–13.0% by volume), mainly improve toughness and thermal performance, with more limited gains in strength. The review also identifies key gaps in the existing literature, such as a lack of standardized protocols for measuring process parameters and the need for studies that address long-term durability and comprehensive lifecycle assessments. These findings outline a clear research roadmap to support the consolidation of reinforced soil–cement as a resilient and sustainable material for next-generation additive manufacturing. Full article

An explicit dynamic framework based on the Nonlocal Macro-Meso-scale Consistent Damage (NMMD) model is proposed to simulate complex multiple-crack evolution in quasi-brittle materials subjected to blast loading. Three numerical examples—a single-edge-notched half-plate, a thick ring, and a hollow mortar cylinder containing a small borehole—are analyzed. The results show that crack initiation, propagation, branching, and coalescence can be naturally captured by the proposed framework without remeshing. Reliable predictions are obtained only when sufficient mesh resolution is used to resolve nonlocal interactions and the time step satisfies the explicit stability criterion. Comparisons indicate that fewer but more dominant crack paths are predicted by the model, suggesting a conservative tendency in estimating the number of fragments. Crack-path selection is significantly influenced by material heterogeneity, which enables secondary cracks to evolve into dominant crack paths. Crack multiplication and network connectivity are promoted by increased blast pressure, whereas crack complexity and spatial extent are reduced by higher damping coefficients. Full article

Concrete structures frequently experience sustained loading during service, which may lead to crack propagation and eventual failure. In this study, three-point bending beams with heights of 200 mm and 300 mm were subjected to sustained load levels of 0.82, 0.84, and 0.86 of the peak load. The crack propagation process was monitored using the Digital Image Correlation (DIC) technique to capture full-field displacement and strain distributions. Analysis of the crack opening displacement (COD) and the fracture process zone (FPZ) revealed that concrete exhibits brittle fracture behavior under sustained loading, with the FPZ not fully developed at creep failure. The crack propagation process was further characterized into three stages. In the initial stage, crack development is mainly governed by viscoelastic deformation. In the intermediate stage, both viscoelasticity and the gradual decay of cohesive stresses within the FPZ contribute to crack growth. In the final unstable acceleration stage, crack propagation is dominated by cohesive stress degradation. Importantly, the crack length at creep failure closely matches the corresponding crack length on the descending branch of quasi-static loading, indicating a direct link between time-dependent creep fracture and quasi-static post-peak behavior. These results provide new insights into the time-dependent fracture mechanics of concrete, revealing the evolution of damage under long-term loading. The study emphasizes material behavior, including FPZ development and stage-wise crack propagation, offering a mechanistic understanding of creep fracture beyond the evaluation of measurement techniques. Full article

This study investigates the mechanical performance and blast resistance of high-performance aramid, carbon, and ultra-high molecular weight polyethylene (UHMWPE) fiber fabrics, responding to the need for lightweight and flexible materials in anti-explosion containers for aviation and critical infrastructure. The experimental methodology integrated quasi-static and dynamic tensile tests to characterize the strain-rate effect, followed by near-field air blast tests on both single-material and hybrid multi-ply fabric specimens to analyze their dynamic response, failure modes, and overpressure attenuation. Key findings revealed that carbon fabric exhibited high stiffness but was strain-rate insensitive and susceptible to brittle perforation failure, whereas aramid and UHMWPE fabrics demonstrated strain-rate sensitivity, with UHMWPE showing superior ductility and energy absorption. The hybrid multi-ply configuration (A-C-U sequence) achieved the least amount of failure, effectively utilizing the wave impedance of aramid fabric for initial shock reflection, high stiffness of carbon fabric for stress homogenization, and plasticity of UHMWPE fabric for energy dissipation. Additionally, all fabrics attenuated peak overpressure by over 80%, with enhancement observed for increased thickness. The study concludes that the strategic layering of different fabrics creates a synergistic effect, mitigating the weaknesses of individual fabrics and establishing an effective design paradigm for advanced blast-resistant structures, further enhancing the protective performance. Full article