Search Results (165)

The human foot adaptively modulates stiffness during walking to balance impact attenuation, arch support, and propulsion, but this function may decline with aging and foot deformity. This study developed a bioinspired insole (bio-insole) for passive rate-adaptive plantar load modulation by embedding shear-stiffening gel (STG) within a Dragon Skin 30 (DS30) silicone elastomer backbone. DS30-STG sandwich specimens were characterized under rate-dependent and cyclic compression. A customized prototype was then evaluated in a preliminary single-case proof-of-concept walking test involving an older adult with sarcopenia, pes cavus, and hindfoot varus tendency, using stock and rigid insoles as comparators. The DS30-STG composite exhibited rate-dependent stiffening, with the apparent compressive modulus increasing from 262.11 to 553.00 kPa as the compression speed increased from 30 to 2000 mm/min, and showed short-term repeatable responses over 100 cycles at 40% strain. Compared with the stock insole, the bio-insole was associated with higher pressure-derived plantar force and peak pressure at the heel, medial arch, and first metatarsophalangeal joint. It also showed lower measured peak electromyography amplitudes of the tibialis anterior and lateral gastrocnemius by 7.8% and 9.3%, respectively, compared with the stock insole. No large observable changes were found in sagittal-plane ankle or knee excursion. These preliminary participant-specific findings suggest that the tested DS30-STG-based insole was associated with altered regional plantar loading and lower-leg muscle activation patterns during walking. Controlled studies with larger cohorts are required to determine reproducibility, tissue-loading safety, functional benefit, and clinical relevance. Full article

Polyethylene (PE) fibers enable engineered cementitious composites (ECCs) to achieve tensile strain-hardening and multiple-cracking behavior through fiber bridging; however, the relatively large crack widths that can develop in PE fiber-reinforced high-strength ECC (HS-ECC) may limit its autogenous self-healing capability. This study therefore establishes a direct link between PE fiber-mediated crack control, matrix micromechanical tailoring, and autogenous self-healing. The critical crack-width thresholds for reliable self-healing were first determined using water sorptivity tests combined with wet–dry cyclic exposure. The results showed that transport properties could be restored to nearly their original levels when crack widths were below approximately 50 μm in tap water and 60 μm in seawater. Based on these thresholds, waste fly ash ceramsite (FAC) was subsequently incorporated to tailor the matrix fracture characteristics and promote saturated multiple cracking under PE fiber bridging. Replacing 20% of quartz sand with FAC increased the tensile strain capacity from 2.75% to 7.14% and the crack number from 17 to 61, while reducing the average crack width from 110 μm to approximately 49 μm. The refined crack pattern enabled reliable autogenous self-healing under wet–dry cycling, with seawater exhibiting particularly favorable healing behavior. These findings provide a micromechanics-based strategy for designing sustainable PE fiber-reinforced HS-ECC with enhanced ductility, crack control, and intrinsic self-healing capability. Full article

A multifunctional hydrogel film, denoted as PCDGPL, was developed for strawberry preservation, and its prospective flexible-sensing capability was evaluated. Distinct from previous systems centered on colorimetric freshness indication or chemically/photocrosslinked sensing networks, PCDGPL employs a physically crosslinked, freeze-thawed PVA/CMC/pectin/β-CD matrix to couple lysozyme-associated antibacterial preservation with NaCl-enabled tensile and compressive deformation responses; a full-formulation-minus-β-CD control further isolated the network-modulating contribution of β-CD. The hydrogel network was proposed to be stabilized by freeze–thaw-induced PVA physical junctions, together with multiple hydrogen-bonding interactions among CMC, pectin, and β-cyclodextrin. Glycerol improved flexibility and moisture retention, NaCl provided ionic conductivity, and lysozyme incorporation contributed to the antibacterial activity of the film. The optimized PCDGPL film showed balanced mechanical properties, stable cyclic tensile/compressive behavior, and reliable strain-dependent resistance responses under stretching and compression. It also exhibited effective antibacterial activity against Escherichia coli and Staphylococcus aureus with good cytocompatibility. In strawberry preservation tests, PCDGPL reduced weight loss to approximately 2.5% and decay rate to 15%, while maintaining approximately 97% of the initial firmness after 10 days. This work provides a promising hydrogel-based active packaging platform for strawberry preservation, together with a prospective capability for mechanical deformation sensing. Full article

Hydrogels used for fracture sealing during heavy-oil thermal recovery are repeatedly exposed to high-temperature steam, dehydration, pressure disturbance, and cooling, conditions that often lead to progressive network deterioration and loss of sealing efficiency. To address this limitation, a thermally triggered self-reinforcing covalent–physical double-network nanocomposite hydrogel was developed by combining a sparse MBAA-crosslinked P(NaAMPS-co-NVP-co-AM) covalent scaffold with a reversible Laponite-mediated physical network. The material response was systematically evaluated through cyclic hydrothermal treatment at 180 °C, while fracture-sealing and resealing performance was examined separately under steam-exposure conditions. Artifact-controlled experiments were further introduced to distinguish genuine cycle-induced reinforcement from dehydration, continued post-curing, and conventional thermal aging. The results show that the NaAMPS/NVP/AM molar ratio of 40/20/40 with 1.00 wt% Laponite provided a suitable balance between precursor processability, hydrothermal stability, and mature network stiffness. After five thermal cycles at 180 °C, the storage modulus of the Lap-DN hydrogel increased from 74.4 to 89.1 kPa, while the compressive stress at 50% strain increased from 0.641 to 0.842 MPa, corresponding to reinforcement ratios of 1.198 and 1.314, respectively. Meanwhile, the mean equivalent pore diameter decreased from 6.2 to 4.8 μm, indicating progressive refinement of the load-bearing network. The hydrogel retained 76.3% of its initial water and 81.6% of its initial volume after five cycles in the reference brine and preserved a cycle-5 modulus retention of 101.3% even at 150,000 mg/L salinity. In fracture-sealing tests, Lap-DN sustained a breakthrough pressure of 3.47 MPa and reduced fracture conductivity by 92.4% in a 1.60 mm fracture. More importantly, the same sealing body maintained a breakthrough pressure of 4.55 MPa after five steam impact–recovery cycles in a 1.20 mm fracture, corresponding to 106.1% of the first-cycle value, while 95.0% of the pre-breakthrough pressure resistance was restored within 30 min of cooling. These results are consistent with a cycle-induced reorganization of the Laponite-mediated physical constraints within the permanent covalent scaffold, although the transient dissociation and reassociation of individual polymer–Laponite junctions were not directly observed. Within this evidence-based interpretation, cyclic thermal perturbation is associated with mechanical reinforcement and repeated fracture resealing rather than acting solely as a damaging factor. This work provides a materials-design strategy for hydrogel sealing systems operating under cyclic steam and high-salinity conditions. Full article

Coastal deltas worldwide are among the regions most vulnerable to land subsidence caused by intensive groundwater extraction, posing serious challenges to urban infrastructure and environmental sustainability. Shanghai exemplifies a typical coastal city experiencing severe land subsidence. Although groundwater abstraction has been strictly regulated and largely prohibited for most purposes, dewatering during deep excavations has become the primary cause of groundwater level fluctuations and the associated soil deformation. This study investigates the deformation mechanisms of Shanghai’s soft soil strata (layers ④ and ⑤₃) under complex groundwater level fluctuations, using a multi-scale experimental approach. Stress-path-controlled triaxial tests were conducted to simulate staged dewatering, repeated dewatering, and artificial recharge processes. The results reveal an approximately linear stress–strain relationship during dewatering, with cumulative irreversible compression observed after cyclic loading. Partial deformation recovery occurred upon recharge, but only at relatively low pressure levels; once the recharge pressure exceeded a certain threshold, considerable axial compression was induced even as radial expansion continued. Microstructural analyses using an Environmental Scanning Electron Microscope (ESEM) and Mercury Intrusion Porosimetry (MIP) show that cyclic effective stress led to the fragmentation of clay aggregates and pore collapse, reducing total pore volume by approximately 10–17%. The deformation mechanism is attributed to the slippage and reorientation of clay particles under face-to-face (F–F) and line-to-face (L–F) contacts. These findings provide critical insights into the multi-scale behavior of soft soils under hydraulic stress and support the development of more sustainable land subsidence mitigation strategies in urban environments. Full article

Instrumented rock-bolt monitoring requires strain records that retain integrity and asset context after local processing and wireless transmission. An Internet of Things (IoT) strain-sensing system with LoRa telemetry and asset metadata was evaluated on a cantilever fixture. The node converted tare-referenced bridge counts to apparent strain, applied temperature compensation using a lagged temperature term, evaluated alarms locally, and buffered summaries for LoRa transfer. Histories were assessed using sequence continuity and a 32-bit cyclic redundancy check (CRC-32). Ten monotonic loading runs showed linear responses to nominal screw advance (R² > 0.9997); fitted slopes had a coefficient of variation of 0.55%. Across three fixed-setting tests spanning 5.1–8.0 °C, unchanged embedded compensation reduced the magnitude of fitted apparent thermal sensitivity by 89.1–95.5%. In all 45 operator-controlled alarm trials, trigger or non-trigger outcomes matched expectations recorded before dashboard inspection. Of 60 planned application-layer history transfers, 50 passed; the remaining ten comprised four failures, three interruptions, and three invalid or contaminated trials. Passed transfers included exact reconstruction of a 1024-record circular buffer. Retrieved metadata passed CRC-32 verification and matched the registered laboratory asset. These results characterize a one-asset laboratory workflow before packaged-bolt, underground, and multi-asset validation. Full article

To improve the seismic performance and post-earthquake recoverability of low- and mid-rise steel frames, this study investigates the seismic performance and layout strategy of a self-centering friction damper (SCFD) through experimental and numerical studies. The SCFD combines the superelastic restoring capability of shape memory alloy (SMA) bars with the energy dissipation provided by non-asbestos organic (NAO) friction materials. Monotonic and cyclic tests were conducted to characterize the mechanical behavior of Ni–50.8 at. % Ti SMA bars and the hysteretic performance of the SCFD, based on which a numerical model of the damper was established and validated. An uncontrolled frame and four controlled frames employing diagonal, chevron, improved lower toggle-brace, and improved upper toggle-brace layouts were comparatively investigated to evaluate the effects of brace configuration, installation position, and damper quantity on seismic performance. The proposed damper exhibited an equivalent damping ratio ranging from 24% to 32%. When the SMA strain exceeded 6%, the residual deformation of the damper increased significantly, indicating that excessive SMA deformation should be avoided in practical design. Among the investigated configurations, the improved upper toggle-brace layout, combined with additional dampers installed at the first story, showed the best overall performance. Compared with the uncontrolled multi-story structure, the residual inter-story drift ratio was reduced by 76.7–93.5%, while the maximum acceleration reduction reached 28.9%. However, local acceleration amplification was observed in some cases because of the increased structural stiffness. These findings provide practical guidance for the layout design and engineering application of self-centering friction dampers in low- and mid-rise steel frames. Full article

Understanding the dynamic evolution of pore and fracture structure (PFS) in coal under mining disturbance is essential for safe coal extraction. In this study, coal specimens collected from the Dongqu Mine, Taiyuan, Shanxi Province, China, were subjected to stepwise cyclic confining pressure loading–unloading tests using a triaxial in situ nuclear magnetic resonance (NMR) system. Based on T₂ spectrum measurements, the real-time evolution of PFS, stress–strain response, permeability-related behavior, average pore diameter, and fractal characteristics were systematically investigated. The results show that irreversible damage developed in the coal specimens during cyclic confining pressure loading–unloading. With increasing cycle number, the load-bearing capacity gradually decreased, internal damage intensified, and pore expansion and coalescence became more pronounced. Seepage pore porosity showed an overall increasing trend, indicating a gradual enhancement of inferred permeability. Therefore, seepage pore porosity can be used as an effective indicator for evaluating permeability-related evolution in coal. During both loading and unloading stages, the relative volumes of small pores (SP), medium pores (MP), and large pores and fractures (LPF) continued to increase, whereas their average pore diameters fluctuated. This indicates that pore volume growth was controlled not only by the enlargement or shrinkage of pre-existing pores but also by new PFS generation. Fractal analysis showed that the fractal dimensions of MP, LPF, and total pores exhibited clear scale-dependent evolution, whereas the calculated SP fractal dimensions were lower than 2 and were therefore not suitable for pore-surface fractal interpretation. Among the valid pore systems, LPF exhibited the highest fractal dimension, indicating that LPF dominate the structural complexity of coal. These findings provide new insight into the fractal evolution of unloading-induced PFS damage and offer theoretical support for mitigating gas outburst and water inrush hazards during coal mining. Full article

Constitutive models for clays have historically treated yield geometry, plastic-flow direction, and compression as separate problems, with little regard for their interaction. This paper presents a controlled numerical assessment of how three components—Chatwong et al.’s verified teardrop yield surface, a stress-fractional flow rule, and an AJOP-derived hardening modulus— interact when coupled in a 2 × 2 × 2 factorial design. The components are integrated incrementally along one idealized shear-strain-controlled constant-p′ path with an approximate undrained variant for two independently calibrated clays (Boston Blue Clay and London Clay) under a specified state-dependent fractional order. Within this scope, the main flow effect is consistently the largest single quantity for both soils, and the flow × compression interaction is comparably large wherever defined. Compression’s role grows substantially with the overconsolidation ratio, and the main geometry effect is markedly soil-dependent, scaling with the surface-shape parameter. Two structural singularities are identified: a phase-transformation point in the teardrop surface’s non-associated flow rule, absent from the fractional rule, and a hardening singularity in the AJOP-based modulus, whose tangent falls to the swelling index at a finite, soil-dependent preconsolidation stress, bounding the evaluable overconsolidation range of the compression-related interactions; a proportional-κ variant removes this singularity by construction while preserving the factorial ranking, identifying it as a property of the constant-κ embedding, not of AJOP itself. Under an approximate undrained path, the geometry × flow interaction carries over unchanged, while compression’s role is suppressed several-fold. The borrowed yield surface and flow rule are validated independently against 379 points from real undrained triaxial tests across four calibrated soils using this paper’s own re-calibrated predictions; the fractional–AJOP framework itself is assessed for internal consistency only, and its laboratory validation, together with K₀, cyclic and multi-axial paths, remains for future work. Full article

This paper presents a modified version of the Booker et al. cycle-based pore pressure generation model for use with strain-controlled cyclic loading tests on sandy soils. The original Booker et al. model has been widely used in geotechnical engineering because of its simplicity and computational efficiency; however, it was developed using stress-controlled cyclic test data and does not accurately capture the pore pressure response observed in strain-controlled cyclic loading. In strain-controlled tests, excess pore pressure typically develops rapidly during the early stages of loading and more gradually as liquefaction is approached, resulting in a pore pressure–cycle ratio relationship fundamentally different from that produced by the original model. To address this limitation, a Modified Booker Model was developed through curve fitting of laboratory test data obtained from strain-controlled cyclic triaxial and cyclic direct simple shear tests. The model was evaluated using the results of 51 cyclic triaxial tests and 101 cyclic direct simple shear tests performed on clean sands and sand–silt mixtures with fines contents both above and below the threshold fines content (TFC). The model produced excellent agreement with measured pore pressure responses, yielding average coefficients of determination (R²) ranging from 0.921 to 0.989 depending on the test type and soil conditions. The results indicate that the Modified Booker Model provides a practical, accurate, and computationally efficient method for predicting pore pressure generation during strain-controlled cyclic loading of sands and silty sands. Full article

This paper investigates the seismic performance of precast concrete shear-wall subassemblies connected by post-cast ultra-high performance concrete (UHPC) zones and short lap-spliced reinforcement with a lap length of $10d$, where d denotes the diameter of the reinforcement bar. Seven quasi-static cyclic tests were conducted, including one cast-in-place control specimen, five specimens with horizontal UHPC back-cast joints at the wall base, and one exploratory specimen with both horizontal and vertical UHPC back-cast joints. The variables considered were the joint arrangement and the axial compression ratio. The specimens with horizontal joints generally exhibited compression-flexure-dominated damage, and the crushing zone shifted from the wall-footing interface to the ordinary concrete immediately above the UHPC back-cast zone. The specimen with the vertical joint (TW6) exhibited bending-shear damage, accompanied by limited in-plane lateral slip at the beam–wall joint and shear damage of several vertical bars. Specimen TW2, with an axial compression ratio of 0.30, was identified as a construction-quality-sensitive case because an insufficient local UHPC cover caused splitting damage and reduced hysteretic stability. The strain measurements indicate that, within the limits of the present instrumentation, the 10d lap in the UHPC zone provided effective stress transfer in the tested specimens; however, direct interface-slip and bond-slip tests are still required for generalized design verification. Under an axial compression ratio of 0.20, TW1 and TW6 showed comparable seismic indices to the cast-in-place specimen, but the conclusions are limited to the tested configurations. All specimens reached ultimate drift ratios greater than 1/100, and their seismic performance is discussed together with failure mode, stiffness degradation, energy dissipation, and connection reliability. Full article

In this study, the microstructural changes and coarsening behavior of Ag₃Sn in Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge (mass%) during high-temperature aging were investigated. Additionally, low-cycle fatigue tests were conducted to compare the fatigue behavior of Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge with that of Sn-3.0Ag-0.5Cu. At room temperature, SbSn phases are dispersed in the β-Sn matrix. As the temperature rises, Sb atoms dissolve in the β-Sn phase; thus, the SbSn phases disappear, and some of the atoms aggregate. The activation energy was 45 kJ/mol for the coarsening of Ag₃Sn in Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge due to aging. Ag₃Sn coarsening was estimated to be controlled by the lattice diffusion of Ag atoms in the β-Sn phase. Furthermore, it was confirmed that the solid solution of Sb atoms in the β-Sn phase reduces the solubility limit of Ag atoms in the β-Sn phase, which delays the coarsening of Ag₃Sn. Regarding fatigue properties, while both alloys exhibited comparable low-cycle fatigue behavior at room temperature, the fatigue ductility exponent’s increase was confirmed to be suppressed for the Sn-6.4Sb-3.9Ag-0.25Ni-0.003Ge alloy at 175 °C. This trend suggests that the delayed coarsening of Ag₃Sn maintains the cyclic strain-hardening exponent, thereby influencing high-temperature fatigue behavior. Full article

This study focuses on the low-cycle fatigue behavior and microstructural damage mechanisms of 316L austenitic stainless steel in cryogenic environments to enhance understanding of its fatigue performance and failure mechanisms over a wide temperature range. Uniaxial tensile and strain-controlled low-cycle fatigue tests were performed at 293 K, 173 K, and 77 K; microstructural evolution and damage mechanisms were explored via interrupted tests combined with multiple microscopic techniques and quantitative martensite analysis. The results show that the room temperature fatigue stress response has three stages, while low temperatures induce continuous cyclic hardening that stabilizes quickly; fatigue life increases with lower temperature and strain amplitude, more notably at high strains. Low temperatures enhance strength, increase hardness, slightly reduce plasticity, but maintain good toughness, suppressing crack initiation and propagation with ductile fracture. The findings clarify cryogenic fatigue damage mechanisms, providing experimental and theoretical support for cryogenic pressure-bearing component design and safety assessment. Full article

3D concrete printing (3DP) enables automated construction with reduced material waste and enhanced geometric flexibility. However, its structural performance remains sensitive to anisotropy, mix design, and printing parameters, thereby complicating quality control. Self-sensing cementitious materials provide a promising approach by enabling intrinsic strain monitoring during fabrication and service. In this study, a hybrid multi-material printing strategy was developed using a conductive cement-based mix incorporating graphite (G), milled carbon microfibers (MCMF), and chopped carbon microfibers (CCMF), alongside a plain cement-based matrix. Based on percolation analysis, an optimal composition of 2 wt.% G, 0.25 wt.% MCMF, and 0.0625 wt.% CCMF was selected. Reinforced beam specimens were fabricated with the conductive material embedded in either the tensile (bottom) or compressive (top) region, combined with two internal architectures: diagonal infill and solid-base configuration. Four configurations were defined: Pattern 1 (bottom/diagonal), Pattern 2 (bottom/solid-base), Pattern 3 (top/diagonal), and Pattern 4 (top/solid-base). Cyclic three-point bending tests with spatially distributed electrical measurements were conducted to evaluate the electromechanical response in the elastic range. Specimens with the conductive layer located in the tensile region (Patterns 1 and 2) consistently exhibited higher gauge factors than those in the compressive region (Patterns 3 and 4). Pattern 2 exhibited the best sensing performance, with an average gauge factor of 556 and SNR of 31. Across all configurations, SNR decreased with increasing electrode spacing, with reductions of up to 31.0%, demonstrating the effect of current path length on sensing performance. Full article

Protective coatings and surface-protection systems improve structural durability, but the long-term performance of durability-sensitive infrastructure also depends on the cyclic stability of supporting soil–rock mixture (SRM) foundations. In this study, undrained multistage strain-controlled cyclic triaxial tests were conducted on reconstructed SRMs with rock block contents of 0%, 10%, 20%, 40%, and 60% under confining pressures of 100, 200, and 400 kPa. Hysteresis-loop morphology, secant shear modulus, normalized shear modulus ratio, damping ratio, normalized damping ratio, and fitting parameters were evaluated. The results show that hysteresis loops evolved from narrow and steep to wider and fuller forms as strain amplitude increased, indicating stiffness degradation and enhanced hysteretic dissipation. The secant shear modulus decreased from 35.835 to 158.871 MPa to 3.296–12.854 MPa, corresponding to an overall reduction of approximately 85%–94%, while the damping ratio increased from 0.036 to 0.063 to 0.195–0.268. Higher rock block content and stronger confinement increased absolute stiffness, but rock block content advanced normalized degradation and damping development, whereas confinement delayed these normalized responses. These findings provide experimental evidence for dynamic-parameter selection, deformation-compatibility evaluation, and cyclic stability assessment of complex SRM foundations. Full article