Search Results (192)

This study introduced basalt fibres as a reinforcing material and employed notched beam three-point bending tests combined with digital image correlation (DIC) technology to comprehensively evaluate key fracture parameters—namely, initial fracture toughness, unstable fracture toughness, fracture energy, and ductility index—of expanded polystyrene (EPS)-based geopolymer concrete with different mix proportions. The results demonstrate that the optimal fracture performance was achieved when the basalt fibre volume content was 0.4% and the EPS content was 20%, resulting in respective increases of 12.07%, 28.73%, 98.92%, and 111.27% in the above parameters. To investigate the toughening mechanisms, scanning electron microscopy was used to observe the fibre–matrix interfacial bonding and crack morphology, while X-ray micro-computed tomography enabled detailed three-dimensional visualisation of internal porosity and crack development, confirming the crack-bridging and energy-dissipating roles of basalt fibres. Furthermore, the crack propagation process was simulated using the extended finite element method, and the evolution of fracture-related parameters was quantitatively analysed using a linear superposition progressive assumption. A simplified predictive model was proposed to estimate fracture toughness and fracture energy based on the initial cracking load, peak load, and compressive strength. The findings provide theoretical support and practical guidance for the engineering application of basalt fibre-reinforced EPS-based geopolymer lightweight concrete. Full article

The identification of structural damage types remains a key challenge in electromechanical impedance/admittance (EMI/EMA)-based structural health monitoring realm. This paper proposed a damage classification approach for concrete structures by using integrating discrete wavelet transform (DWT) decomposition of EMA signatures with supervised machine learning. In this approach, the EMA signals of arranged piezoelectric ceramic (PZT) patches were successively measured at initial undamaged and post-damaged states, and the signals were decomposed and processed using the DWT technique to derive indicators including the wavelet energy, the variance, the mean, and the entropy. Then these indicators, incorporated with traditional ones including root mean square deviation (RMSD), baseline-changeable RMSD named RMSDk, correlation coefficient (CC), and mean absolute percentage deviation (MAPD), were processed by a support vector machine (SVM) model, and finally damage type could be automatically classified and identified. To validate the approach, experiments on a full-scale reinforced concrete (RC) slab and application to a practical tunnel segment RC slab structure instrumented with multiple PZT patches were conducted to classify severe transverse cracking and minor crack/impact damages. Experimental and application results cogently demonstrated that the proposed DWT-based approach can precisely classify different types of damage on concrete structures with higher accuracy than traditional ones, highlighting the potential of the DWT-decomposed EMA signatures for damage characterization in concrete infrastructure. Full article

The fatigue resistance of cement-stabilized macadam (CSM) plays a vital role in ensuring the long-term durability of pavement structures. However, limited cementitious material (CM) content often leads to high packing voids, which significantly compromise fatigue performance. Existing studies have rarely explored the coupled mechanism between pore structure and fatigue behavior, especially in the context of solid-waste-based CMs. In this study, a cost-effective alkali-activated sludge gasification slag (ASS) was proposed as a sustainable CM substitute for ordinary Portland cement (OPC) in CSM. A dual evaluation approach combining cross-sectional image analysis and fatigue loading tests was employed to reveal the effect pathway of void structure optimization on fatigue resistance. The results showed that ASS exhibited excellent cementitious reactivity, forming highly polymerized C-A-S-H/C-S-H gels that contributed to a denser microstructure and superior mechanical performance. At a 6% binder dosage, the void ratio of ASS–CSM was reduced to 30%, 3% lower than that of OPC–CSM. The 28-day unconfined compressive strength and compressive resilient modulus reached 5.7 MPa and 1183 MPa, representing improvements of 35.7% and 4.1% compared to those of OPC. Under cyclic loading, the ASS system achieved higher energy absorption and more uniform stress distribution, effectively suppressing fatigue crack initiation and propagation. Moreover, the production cost and carbon emissions of ASS were 249.52 CNY/t and 174.51 kg CO₂e/t—reductions of 10.9% and 76.2% relative to those of OPC, respectively. These findings demonstrate that ASS not only improves fatigue performance through pore structure refinement but also offers significant economic and environmental advantages, providing a theoretical foundation for the large-scale application of solid-waste-based binders in pavement engineering. Full article

To explore the influence of mine roof on the damage and failure of sandstone surrounding rock under different pressure rates, mechanical experiments with different strain rates were carried out on sandstone rock samples. The strength, deformation, failure, energy and damage characteristics of rock samples with different strain rates were also discussed. The research results show that with the increases in the strain rate, peak stress, and elastic modulus show a monotonically increasing trend, while the peak strain decreases in the reverse direction. At a low strain rate, the proportion of the mass fraction of complete rock blocks in the rock sample is relatively high, and the shape integrity is good, while rock samples with a high strain rate retain more small-sized fragmented rock blocks. This indicates that under high-rate loading, the bifurcation phenomenon of secondary cracks is obvious. The rock samples undergo a failure form dominated by small-sized fragments, with severe damage to the rock samples and significant fractal characteristics of the fragments. At the initial stage of loading, the primary fractures close, and the rock samples mainly dissipate energy in the forms of frictional slip and mineral fragmentation. In the middle stage of loading, the residual fractures are compacted, and the dissipative strain energy keeps increasing continuously. In the later stage of loading, secondary cracks accelerate their expansion, and elastic strain energy is released sharply, eventually leading to brittle failure of the rock sample. Under a low strain rate, secondary cracks slowly expand along the clay–quartz interface and cause intergranular failure of the rock sample. However, a high strain rate inhibits the stress relaxation of the clay, forces the energy to transfer to the quartz crystal, promotes the penetration of secondary cracks through the quartz crystal, and triggers transgranular failure. A constitutive model based on energy damage was further constructed, which can accurately characterize the nonlinear hardening characteristics and strength-deformation laws of rock samples with different strain rates. The evolution process of its energy damage can be divided into the unchanged stage, the slow growth stage, and the accelerated growth stage. The characteristics of this stage reveal the sudden change mechanism from the dissipation of elastic strain energy of rock samples to the unstable propagation of secondary cracks, clarify the cumulative influence of strain rate on damage, and provide a theoretical basis for the dynamic assessment of surrounding rock damage and disaster early warning when the mine roof comes under pressure. Full article

This study explores the mechanical performance of triply periodic minimal surface (TPMS) and stochastic lattice structures subjected to low-velocity impact. Two structurally promising geometries—one TPMS-based and one stochastic—were tested and compared with the well-established gyroid. Specimens were fabricated using stereolithography (SLA) and subjected to impact energies of 30 J and 40 J to assess the structural response and energy absorption capabilities. Experimental results show that the proposed TPMS structure exhibits higher impact forces compared with the gyroid, which are associated with significant impactor displacement and deep indentation. These samples demonstrated extensive damage, with cracking propagating through the entire core at higher energies, highlighting their susceptibility to structural failure despite their high initial strength. On the contrary, the stochastic structures allowed localized deformation in the impacted region, thus successfully avoiding catastrophic failure. The impact force efficiency was higher for both gyroid and stochastic geometries, with values ranging between 0.6 and 0.7, indicating effective energy absorption with reduced internal stress gradients. Furthermore, the evaluation of damping performance showed that most structures displayed high damping, as minimal energy was transferred back to the impactor. This work highlights the feasibility and functional versatility of TPMS and stochastic geometries for use in impact mitigation, vibration control, and related engineering applications. Full article

This study explores the feasibility of manufacturing martensitic stainless steel turbine blades via a directed energy deposition (DED) process using a powder precursor. Five different blade geometries were fabricated using AISI 431 L martensitic stainless steel deposited onto an AISI 304 L austenitic stainless steel substrate. The produced components were characterized in terms of microstructure, surface roughness, porosity, hardness, and residual stresses in both the as-processed condition and after heat treatment at 260 and 593 °C. Optical and scanning electron microscopy (SEM) analyses revealed a predominantly martensitic microstructure with well-defined grain boundaries. Heat treatment influenced the phase distribution and grain size, but did not have a significant impact on the surface roughness or modulus of elasticity. Tomographic assessments confirmed the absence of aligned or coalesced pores, which are critical sites for crack initiation. Residual stress analysis indicated the presence of compressive stresses in all blade geometries, which were effectively relieved by heat treatment. In addition, salt spray corrosion tests demonstrated that the corrosion resistance of the manufactured blades was similar to that of the base material. These findings suggest that DED is a viable technique for producing and repairing turbine blades, providing structural integrity and mechanical properties suitable for high-performance applications. Full article

This study investigated the effect of coarse cement on the self-healing ability of mortar. Coarse cement, prepared via negative-pressure screening, was substituted (0–40%) in mortar mixes with water/cement (w/c) ratios of 0.45–0.55. The specimens were cured for 28 days, cracked, and allowed to self-heal for another 28 days. Self-healing was evaluated based on compressive strength recovery and ultrasonic pulse velocity. At a 0.50 w/c ratio, 10% coarse cement substitution achieved 87.7% strength recovery (21.2 MPa increase), outperforming the control group (74.1%, 13.0 MPa). Reducing the w/c ratio to 0.45 further enhanced recovery to 89.4% (21.5 MPa). While coarse particles alone reduced the initial strength, combining their addition (e.g., 10%) with a lower w/c ratio (0.45) improved self-healing without significant strength loss. Based on the Krstulović–Dabić model and a micro-geometric model incorporating hydration units, this study analyzed the intrinsic self-healing mechanism of cement-based materials through computational results. Theoretical calculations demonstrated that during cement hydration, coarser particles can form a microcapsule-like structure where hydration products encapsulate unhydrated cement. The findings suggest that optimizing coarse particle content and the w/c ratio can balance self-healing enhancement and mechanical performance, offering a viable strategy for energy saving and emission reduction by reducing the carbon emissions per unit of service life and the grinding process in cement production. Full article

The prefabricated concrete channel, constructed by integrating factory-based prefabrication with on-site assembly, offers enhanced quality, reduced construction time, and minimized environmental impact. To promote its application in water conservancy projects, an innovative concrete joint combining semi-grouting sleeves and shear-resistant steel plates was proposed. Its seismic performance was assessed through a 1:3 scale low-cycle reversed loading test, focusing on failure mode, hysteretic behavior, skeleton curves, stiffness degradation, ductility, and energy dissipation. Results show that the joint primarily exhibits bending–shear failure, with cracks initiating at the sidewall–base slab interface. Also, the sidewall and base slab are interconnected through semi-grouting sleeves, while the concrete bonding is achieved via grouting and surface chiseling at the joint interface. The results indicated that the innovative concrete joint connection exhibits satisfied seismic performance. The shear-resistant steel plate significantly improves shear strength and enhances water sealing. Compared with cast-in-place specimens, the prefabricated joint shows a 16.04% lower equivalent viscous damping coefficient during failure due to reinforcement slippage, while achieving 16.34% greater cumulative energy dissipation and 52.00% higher ductility. These findings provide theoretical and experimental support for the broader adoption of prefabricated channels in water conservancy engineering. Full article

This study investigates the fatigue durability of Plexus MA300 methacrylic adhesive, which is employed in structural joints of metals, plastics, and composites. Cast adhesive specimens were subjected to cyclic tensile loads at a frequency of 5 Hz with a stress ratio R = 0.1. Six load levels were tested. Hysteresis loops were recorded during testing and analyzed in detail. Significant differences in fatigue fracture characteristics were observed depending on load level. Specimens subjected to high loads exhibited a characteristic radial structure with a distinct crack initiation point, whereas specimens tested at lower loads showed more uniform, matte fracture surfaces. Hysteresis loop analysis revealed phenomena typical for polymers: creep and damping causing energy dissipation. Various fatigue approaches were compared: stress-based, strain-based, energy-based, and stiffness-based. The highest coefficient of determination (R²) was obtained for the model based on strain energy density, indicating its superior utility in predicting the fatigue life of the tested adhesive. The obtained results contribute to the understanding of the fatigue behavior of methacrylic adhesives and provide practical data for structural joint design involving this material class. Full article

Seismic resilience is a critical concern in the development of prefabricated concrete structures. This study investigates the seismic performance of prestressed prefabricated concrete frames with mechanically connected steel bars through both experiment and finite element simulations using ABAQUS. The research aimed to evaluate the influence of prestressed and mechanical connections on structural stiffness, energy dissipation and failure mechanisms, and a restoring force model was developed based on the experimental and numerical results to provide a theoretical basis for seismic design. The parametric analysis based on the verified numerical model shows that the pretension can significantly enhance the bearing capacity, stiffness and deformation recovery ability of the prefabricated concrete frames. The peak load increased by 30.8%, the initial stiffness improved by 17.4%, the ductility coefficient reached 2.82, the residual deformation rate reduced by 40.7%, the emergence and development of cracks delayed, and the crack width reduced. Improving the effective prestress in a certain range can improve the bearing capacity and initial stiffness of the frame. Increasing the strength of concrete and the ratio of the longitudinal reinforcement of beam and column can effectively enhance the bearing capacity of the frame. With the increase of axial compression ratio in a certain range, the bearing capacity and initial stiffness of the frame increase significantly, but the ductility decreases. Based on the hysteresis curve and skeleton curve tested, the skeleton curve model and stiffness degradation law of the prestressed prefabricated concrete frames reinforced with mechanical connection steel bars were fitted, and the restoring force model was established. The predicted value was in good agreement with the experimental value, illustrating the validity of the model developed. These results offer valuable insights for optimizing the seismic design of prefabricated concrete frames, ensuring a balance between strength, stiffness, and ductility in earthquake-resistant structures. Full article

In laser-directed energy deposition (LDED) additive manufacturing, stress-induced deformation and cracking often occur unexpectedly, and, once initiated, they are difficult to remedy. To address this issue, we previously proposed the Dynamic Counter Method (DCM), which monitors internal stress based on deposition layer shrinkage, enabling real-time stress monitoring without damaging the component. To validate this method, we used AlSi10Mg material, which has a low melting point and high reflectivity, and developed a high-precision segmentation network based on DeeplabV3+ to test its ability to measure shrinkage in high-exposure images. Using a real-time reconstruction model, stress calculations were performed with DCM and thermal–mechanical coupling simulations, and the results were validated through XRD residual stress testing to confirm DCM’s accuracy in calculating internal stress in aluminum alloys. The results show that the DeeplabV3+ segmentation network accurately extracted deposition-layer contours and shrinkage information. Furthermore, DCM and thermal–mechanical coupling simulations showed good consistency in residual stress distribution, with all results falling within the experimental error range. In terms of stress evolution trends, DCM was also effective in predicting stress variations. Based on these findings, two loading strategies were proposed, and, for the first time, DCM’s application in online stress monitoring of large LDED components was validated, offering potential solutions for stress monitoring in large-scale assemblies. Full article

The dynamic response and failure of rubber-coated sandwich composite structures with buoyancy material core (RC-BMC-SCS) subjected to high-energy low-velocity impacts were experimentally and numerically investigated. Six types of BMC-SCSs were designed and manufactured, and high-energy low-velocity impact experiments were performed. Based on the Mohr-Coulomb theory and the Ogden hyperelasticity constitutive model, a low-velocity impact finite element analysis model was developed. The results indicate that BMC-SCS damage stages could be divided into: (1) matrix damage, (2) core cracks, (3) debonding and fiber breakage. Three distinct damage stages of the RC-BMC-SCS were revealed: (1) rubber layer energy absorption, (2) core cracks, (3) debonding. The rubber layer can enhance the damage threshold by approximately 100% compared to BMC-SCS. However, rubber energy absorption capacity has an upper limit. Additionally, the larger the curvature of the BMC-SCS, the higher the initial stiffness of the structure and the larger the impact damage area. The results of this study provide valuable insights for the multifunctional design of composite deep-sea marine structures. Full article

This study develops a fracture energy-based finite element model to assess top-down cracking (TDC) in asphalt pavements, integrating aging, healing, and interlayer bonding effects through viscoelastic fracture mechanics. Computational analyses of typical Chinese materials and structures reveal that SMA-13 surface layers improve TDC resistance by 19.8% compared to conventional AC-25 mixtures in 17 cm thick pavements. Thicker asphalt layers (20 cm) extend crack initiation life by 16.2% under standard axle loads. UV radiation reduces TDC life by 1.55–2.60%, concentrating 82% of cracks in wheel-path zones. Anti-aging agents restore 47% of fracture energy loss, maintaining stable energy dissipation ratios (EDR > 0.75) beyond 50 months. Poor bonding consumes 19.1% of TDC life, with crack density in wheel paths 3.2× higher than in non-wheel areas. Critical thresholds are identified: longitudinal wheel-path zones require 12% higher fracture energy to prevent crack initiation compared to transverse zones. The model demonstrates that combining ≥18 cm asphalt layers, polymer-modified surfaces (PG76-22), and chemical stabilizers (e.g., 1.5% Sasobit) reduces aging-induced TDC risks by 34–41%. These findings provide mechanics-based guidelines for designing durable pavements in freeze-thaw regions. Full article

To investigate the reinforcement effects of different reinforcement methods including basalt fibers on unreinforced masonry walls (UMWs), this study examined three reinforcement methods: ordinary mortar, basalt fiber mortar, and basalt fiber mesh mortar. Three masonry wall specimens were designed: ordinary mortar surface-strengthened masonry wall (O-MW), basalt fiber mortar surface-strengthened masonry wall (BF-MW), and basalt fiber mesh mortar surface-strengthened masonry wall (BFM-MW). Quasi-static tests were conducted to analyze the failure phenomena, hysteresis curves, backbone curves, energy dissipation capacity, and stiffness degradation. The results show that, compared to O-MW, BF-MW exhibited a 10.3%, 1.5%, and 28.1% increase in cracking load, peak load, and energy dissipation capacity, respectively. Meanwhile, BFM-MW showed more pronounced improvements, with cracking load and peak load increasing by 41.6% and 3.9%, respectively, and initial stiffness rising by 32.8%. However, this method shifted the failure mode of masonry walls from flexural failure to shear failure. Both basalt fiber mortar reinforcement methods outperformed ordinary mortar, each demonstrating distinct characteristics that can be selected based on practical application requirements. Full article

In this paper, specimens that contain cavities are tested and the critical force for crack initiation is compared to predictions made by the Coupled Criterion (CC). First, the material parameters Young’s modulus, Poisson’s ratio, fracture toughness, and critical stress are calibrated with tensile tests of three specimen shapes. Then, the critical force and crack initiation position are predicted for three other specimen shapes, called validation specimens. The predictions made by CC use stresses and incremental energy release rates that are computed by the Finite Element Method (FEM) and the Scaling Law based Meta Model (SLMM+AC). The predictions are validated against the tensile test results of the validation specimens. A Monte Carlo approach is used to compute prediction intervals for the critical force to make a statement about the quality of the predictions. The position of the crack initiation was predicted accurately, but the predicted critical loads deviated from the measured load up to 25%. Full article