Search Results (326)

The degradation of concrete under wetting–drying cycles significantly compromises the safety and durability of bridge structures; however, existing constitutive models often exhibit limitations in practical engineering applicability. To improve the engineering applicability of existing constitutive models, this study proposes a porosity-dependent uniaxial compressive constitutive model for concrete located in the wetting–drying zones of in-service bridge piers. This model is theoretically grounded in the strain equivalence principle and the Weibull statistical distribution. To validate the theoretical framework, six groups of concrete specimens with varying target porosities (15%, 20%, and 25%) were subjected to 15 consecutive 30-day sulfate wetting–drying exposure intervals, corresponding to a total exposure duration of 450 days. The macroscopic evolutions of porosity, mass variation, permeability coefficients, and uniaxial compressive stress–strain behavior were systematically evaluated. Furthermore, an independent field validation was conducted utilizing core samples extracted from the Saiqi Bridge, an in-service structure exposed to natural water-level fluctuations over a 25-year service period. The experimental results indicate that the theoretical stress–strain relationships predicted by the proposed model are in good agreement with the empirical measurements. In the field application, the core data revealed a reduction in concrete compressive strength from the initial design value of 40 MPa to 38.2 MPa. The porosity inversely predicted by the proposed model (16.9%) showed good agreement with the actual measured porosity (17%) of the bridge piers. By explicitly incorporating pore characteristics, the proposed model characterizes the mechanical deterioration of concrete. Consequently, it provides theoretical support for the performance assessment, numerical simulation, and structural strengthening of in-service bridges exposed to repeated wetting–drying exposure. Full article

Mechanical loading of connective tissues is traditionally prescribed by force magnitude. In viscoelastic tissues, a constant external force does not produce a constant internal mechanical environment: stress and strain evolve continuously after load onset, creating a time-varying tissue-level mechanical history relevant to resident cells. This distinction is rarely accounted for in clinical loading protocols or scaffold design. The rate of evolution is governed by the stress relaxation time constant (τ). How τ controls the persistence of mechanical signals under force-controlled sustained loading remains poorly quantified. Thus, we developed a three-dimensional finite element model of the Wistar rat maxillary first molar tooth–periodontal ligament (PDL)–bone complex with a PDL geometry reconstructed from micro-CT imaging by original frame-by-frame manual segmentation and compared outcomes across three τ values spanning two orders of magnitude under identical 0.5 N sustained loading. Under the same applied force, stress retention at 100 s ranged from 68% to 97%, while concurrent deformation creep showed an inverse relationship. These results demonstrate that τ strongly governs the persistence of mechanical signals under sustained force-controlled loading in this model. Supplementary simulations under oblique loading and perturbed PDL modulus confirmed that τ remains the dominant constitutive determinant of stress retention across altered loading directions and stiffness conditions. Full article

The pressuremeter test (PMT) measures in situ soil properties under the original stress state with minimal disturbance. However, interpreting PMT data for constitutive parameters remains reliant on empirical correlations, and a key challenge is the poorly understood size effect arising from the equipment dimensions. This study aims to systematically quantify such size effects to provide a scientific basis for optimizing the design of laboratory PMTs. A series of 36 PMT simulations were performed using the finite element method (FEM), incorporating the Duncan–Chang E-B hyperbolic model. Six cylindrical soil models of diameters ranging from 0.6 m to 2.4 m were established for both sand and clay, under three overburden pressures (200 kPa, 1000 kPa and 3000 kPa). The radial stress, strain distributions and borehole wall displacement were systematically analyzed. The analysis reveals that the size effect originates from the truncation of the radial strain integration path. In all cases, borehole wall displacement increases with model diameter, characterized by a steep rise for diameters below 1.2 m and a plateau for those above 1.2 m. Although clay produces larger displacements than sand, and higher stress produces larger displacements than lower stress, the identified pattern remains robust. Considering both the displacement–diameter relationship and practical cost constraints, an optimal equipment diameter of 1.2 m is recommended. Full article

Expansion joint anchorage zones are prone to premature cracking and fatigue deterioration under repeated wheel impact and interfacial stress concentration. Engineered cementitious composites (ECCs) are promising anchorage materials because of their tensile strain-hardening behavior, multiple fine cracking, and high deformation capacity. However, how ECC strength–ductility characteristics affect vehicle-induced stress redistribution and fatigue damage accumulation remains unclear. This study develops a material–structure–fatigue framework for ECC anchorage zones. Three PVA-ECC mixtures were tested, and their measured constitutive relationships were incorporated into a three-dimensional vehicle–expansion joint coupled finite element model validated using reported field strain data from a C50 concrete anchorage zone. Critical tensile stress histories were extracted for rainflow counting and Miner-based fatigue assessment. Results show that ECC reduced tensile stress concentration and increased tensile safety margins compared with C50 concrete. Under the defined loading scenario, the estimated fatigue life increased from 9.93 years for C50 concrete to 83.15 years for the best-performing ECC scheme. Ten-year comparative field observations supported the predicted durability trend. By linking ECC strength–ductility characteristics with vehicle-induced stress redistribution and cumulative fatigue damage, the proposed framework provides a quantitative basis for fatigue-resistant material selection and durability-oriented design of expansion joint anchorage zones. Full article

The cyclic material properties are crucial for accurate assessment of structural response; however, conventional numerical methods often fail to replicate the mechanical degradation caused by ultra-low cycle fatigue (ULCF) damage accumulation. This paper focuses on a novel constitutive model characterizing the continuous degradation in yield stress and stiffness under large-strain tension–compression cyclic loads. A series of 32 cyclic tests on circular notched specimens covering a range of stress triaxialities are first revisited to systematically identify the cyclic softening behavior. The corresponding limitations of the widely applied classical Chaboche theory are examined, and an enhanced elastoplastic constitutive framework is proposed accordingly. On this basis, the stress-weighted ductile fracture model (SWDFM), which is developed from micro-damage mechanics, is then employed as the internal damage criterion of the proposed constitutive model. Explicit functional relationships linking the evolved yield stress and Young’s modulus to the imposed damage index are established and calibrated against the test data. Based on these findings, a new cyclic ductile constitutive model is developed, which is programmed into the UMAT subroutine compatible with ABAQUS/Standard. Numerical validations against the experimental cyclic responses exhibit good agreement, as indicated by the considerably low average errors of 5% for both strength and stiffness, demonstrating its validity in terms of the hysteretic behavior simulation for metals subjected to progressive ULCF damage. Full article

Coal-mining-induced goaf areas are widely distributed in China and pose potential risks to high-speed railways. Repeated train-induced cyclic loading may further disturb the already weakened ground and aggravate deformation of the subgrade. A study on the goaf ground soil along the Taijiao High-Speed Railway utilized a GDS dynamic triaxial apparatus and controlled variable method to examine how waveforms, cyclic stress ratios (CSRs), effective confining pressures, vibration frequencies and cycles affect soil dynamics. The results show that cumulative plastic strain and residual pore pressure ratio generally tended to stabilize after rapid early development; however, both responses increased markedly within the 2–3 Hz frequency range. Among the investigated variables, the cyclic stress ratio (CSR) exerted the most significant influence and showed an exponential relationship with cumulative plastic strain and residual pore pressure ratio, whereas effective confining pressure produced a nearly linear decreasing trend. A dynamic stress–strain backbone curve was constructed, and by introducing the influence of vibration cycles into the H-D framework, the modified model achieved better agreement with the experimental backbone curves than the conventional H-D model. Furthermore, ABAQUS simulations further demonstrated that train speed and subgrade form significantly influence the distribution of dynamic stress and vertical displacement in goaf ground, with a more severe response in the cutting section. The optimized constitutive model and numerical results provide theoretical support for foundation design, long-term stability assessment and settlement prediction of high-speed railways constructed over goaf ground. Full article

Lunar regolith simulant (LRS) geopolymers are promising construction materials for lunar in situ resource utilization, but their brittle behavior and limited crack resistance restrict their structural applications. This study investigated the effect of basalt fiber length on the mechanical properties, failure modes, stress–strain behavior, constitutive relationship, and microstructure of CQU-1 LRS geopolymers. Basalt fiber-reinforced LRS geopolymers were prepared under weak alkali activation and high-temperature curing at 80 °C. The basalt fiber content was fixed at 0.1%, and six fiber lengths of 0, 6, 9, 12, 15, and 18 mm were considered. Compressive and flexural tests were conducted after curing for 1 d and 7 d, and the normalized stress–strain curves were fitted using the Saenz L.P., Carreira D.J., and Zhenhai Guo models. The results showed that basalt fiber length significantly affected the mechanical performance of LRS geopolymers. An appropriate fiber length improved strength, stiffness, ductility, and post-peak load-bearing capacity, whereas excessively short or long fibers weakened the reinforcing effect. The 15 mm fiber group exhibited the best overall performance. After curing for 1 d, its compressive strength reached 2.23 MPa, 49.7% higher than that of the control group, and its elastic modulus increased approximately 2.5-fold. After curing for 7 d, its compressive strength reached 13.44 MPa, 32.0% higher than that of the control group. The Zhenhai Guo model provided the best fit for the stress–strain curves. SEM-EDS analysis showed that basalt fibers improved interfacial bonding and promoted gel enrichment near the fiber–matrix interface. Overall, 15 mm was recommended as the optimal basalt fiber length for CQU-1 LRS geopolymers under the conditions used in this study. Full article

Loess in seasonally frozen regions is prone to water-induced softening and dynamic instability, posing severe challenges for geotechnical engineering. Rubber particles, as sustainable waste-tire-derived material, offer potential for loess improvement. This study aims to elucidate the dynamic characteristics and modulus attenuation evolution of rubber particle–loess mixtures under multi-factor coupling effects. Dynamic triaxial tests were conducted to investigate the influences of rubber content, particle size, moisture content, and freeze–thaw cycles. Results reveal that the optimal mix is 5% rubber content with 40-mesh rubber particles, which yields the highest dynamic strength (i.e., the maximum dynamic stress that can be sustained before failure). The dynamic constitutive relationship follows the Hardin–Drnevich hyperbolic model. Increased moisture content and more freeze–thaw cycles reduce the maximum dynamic elastic modulus and strain, while higher confining pressure enhances them. A dynamic elastic modulus attenuation model was established to characterize strain-softening behavior. These findings clarify the dynamic response mechanisms of modified loess, providing a theoretical basis for its engineering application in seasonally frozen regions. Full article

Existing analytical models for Fiber-Reinforced Polymer (FRP)-strengthened timber beams are generally limited to individual strengthening techniques and cannot readily accommodate hybrid reinforcement systems. This study develops a generalized analytical model to predict the flexural capacity of timber beams strengthened with near-surface-mounted (NSM) FRP bars, externally bonded FRP sheets, or their hybrid combination within a unified theoretical framework. The model is formulated based on internal force equilibrium and strain compatibility, incorporating a constitutive model for timber with linear elastic tensile behavior and a bilinear compressive stress–strain relationship including post-peak softening. The generalized formulation can be readily adapted to different strengthening configurations through appropriate simplifications. The proposed model was validated against experimental results obtained from four-point bending tests on small-scale timber beams strengthened with NSM GFRP bars and externally bonded GFRP sheets. The analytical predictions showed good agreement with the experimental results, with differences generally ranging from 2% to 23%, demonstrating satisfactory predictive accuracy. The experimental results further showed that the hybrid strengthening system increased the flexural capacity of the timber beams by up to 84% compared with the unstrengthened control beams, while also improving stiffness, ductility, and overall structural response. Failure was primarily due to timber tensile rupture and longitudinal splitting, whereas the GFRP reinforcement remained effective without rupture, indicating efficient utilization of the strengthening system. The proposed generalized analytical model provides a practical and reliable design tool for predicting the flexural strength of timber beams strengthened with various FRP reinforcement configurations, thereby supporting the structural rehabilitation and sustainable retrofitting of timber structures. Full article

Q420 high-strength steel exhibits pronounced anisotropy due to its rolling process, and conventional uniaxial tensile testing is incapable of acquiring strain field evolution information during the local necking stage. In this study, quasi-static uniaxial tensile tests were conducted on Q420 cold-rolled high-strength steel sheets at six orientations (0°, 15°, 30°, 45°, 60°, and 90°) using Digital Image Correlation (DIC) technology. The evolution of the strain field and the corresponding stress–strain responses at different orientations were systematically investigated. The results show that the DIC technique effectively captured the full-field strain evolution of the specimens from uniform deformation to local necking and final fracture in all directions. Taking the 0° direction as an example, the local maximum engineering strain prior to fracture reached 35.866%, whereas the average fracture strain within the gauge section was only approximately 22.5%, corresponding to a ratio of approximately 1.6 and clearly demonstrating the severe strain concentration within the necking zone. The stress–strain curves corresponding to different rolling directions exhibited pronounced anisotropy. The tensile strength was highest in the 90° direction and lowest in the 0° direction; however, the 0° direction exhibited the best ductility, whereas the 45° direction showed the poorest ductility. Among the six orientations, the midpoint transverse engineering strain exhibited the largest absolute value in the 45° direction, further indicating that this orientation is the most susceptible to plastic instability. In this work, DIC-based full-field measurement was combined with multi-directional tensile testing to quantitatively characterize the relationship between local strain concentration and anisotropy. The findings provide high-precision experimental data for the calibration of anisotropic constitutive models and the optimization of forming processes. Full article

Future lunar missions, like the International Lunar Research Station (ILRS), demand single-launch multi-point operations, urgently requiring reusable energy-absorbing structures. Integrating shape memory alloy (SMA) into honeycombs offers a promising solution; however, deformation exceeding the SMA’s recoverable limit induces structural residual deformation, altering the configuration and degrading subsequent energy absorption. To address this, we propose a semi-analytical, data-calibrated hybrid model predicting SMA honeycomb residual deformation. A four-stage linear constitutive model is established capturing superelasticity and martensitic yielding. Cell walls are idealized as equivalent beams. Using layered fiber integration and numerical interpolation, a nonlinear moment–curvature relationship is constructed, enabling rapid structural residual deflection evaluation from material residual strains. Finite element results confirm that initial residual deformation stabilizes the honeycomb into a reusable configuration, governing subsequent plateau stresses. Calibrated by uniaxial test data, the proposed model accurately predicts residual deformation ratios and reusable plateau stresses with errors within 8%. By bridging material-level strain with structural-level deformation, this approach circumvents computationally expensive full-scale simulations and costly experimental trials, providing a highly efficient tool for designing reusable SMA absorbers. Full article

Background/Objectives: The family constitutes a primary ecological system shaping infant emotional and mental health. Parent responsiveness in particular shapes early regulatory capacities in the developing child. Added contextual stress such as that associated with natural disasters may strain caregiving relationships. Brief, universally accessible parenting interventions offer scalable support for strengthening early relational health and may be useful in contexts of natural disaster-related stress as well as in the general population. This qualitative study examined the perceived impact and contextual relevance of MERTIL (My Early Relational Trust-Informed Learning) for Parents, a brief digital psychoeducational parenting program targeting early relational health, among families raising young children in disaster-affected communities. Methods: Fourteen parents residing in the Hunter New England and Central Coast region of New South Wales, Australia, with young children aged 0–5 years, participated in semi-structured interviews conducted approximately 6 months after completing MERTIL for Parents. Interviews explored lived experiences of parenting in the context of natural disaster (analysed via applied phenomenological methods) and parents’ perceptions of program components that supported everyday caregiving (analysed via reflexive thematic analysis and content analysis). Results: Parents described interconnected personal, relational, and environmental stressors that influenced aspects of the parent–infant relationship. Key retained knowledge from the program included a normalisation of parenting challenges, a strengthened understanding of attachment, trust, safety and repair, and attuned, emotion-focused parenting practices. Conclusions: This pilot study illuminates the lived experience of parenting in disaster prone regions and highlights the potential for this brief, universal digital parenting program to provide support for early relational health in such contexts. Full article

Ultra-high-performance concrete (UHPC) has attracted extensive attention because of its superior mechanical performance and durability. However, many existing tensile constitutive models are still obtained mainly by fitting macroscopic stress–strain curves, and the coupling among tensile damage development, steel-fiber parameters, and structural-scale response has not been sufficiently clarified. In this work, an acoustic-emission-informed tensile damage model was established for UHPC. Direct tensile tests were carried out on UHPC specimens containing steel fibers with aspect ratios of 43, 65, and 100 and volume fractions ranging from 0.5% to 3.0%, while acoustic emission signals were collected during loading. The normalized cumulative AE count was adopted as a damage indicator, and its evolution with tensile strain was described using a Weibull-type function. A fiber factor combining fiber volume fraction and aspect ratio was further incorporated into the damage constitutive equation. The proposed relationship was checked against 14 independent tensile datasets reported in the literature. After correction, the mean relative error of the predicted model parameter was reduced to 2.6%, with a standard deviation of 4.1%, and the fitted stress–strain curves all achieved R² values above 0.85. The constitutive model was then implemented in ABAQUS for the simulation of reinforced UHPC beams. By introducing a member-level reduction coefficient of μ = 0.84, the numerical load–deflection curve showed improved agreement with the experimental beam response. The coefficient is empirical and is applicable only to the beam configuration investigated here unless further validation is performed. Overall, the proposed model provides a damage-based link among AE monitoring, steel-fiber reinforcement parameters, and member-scale numerical analysis. Full article

Glass fiber–reinforced polymer (GFRP) reinforcement provides an effective alternative to conventional steel in concrete structures due to its corrosion resistance. Nevertheless, the lower elastic modulus of GFRP necessitates careful consideration of serviceability behavior in GFRP-reinforced concrete members. This study presents a numerical sectional analysis model for predicting the flexural response and ultimate capacity of hybrid reinforced concrete beams incorporating embedded GFRP profiles in combination with either mild steel or GFRP reinforcement bars under monotonic static loading. The proposed model employs realistic nonlinear stress–strain relationships for concrete and steel, together with secant moduli of elasticity evaluated at different loading stages. Particular emphasis is placed on detailed stress distribution in flexural sections, including the contribution of tension stiffening in the post-cracking regime. The formulation integrates nonlinear constitutive material behavior with theoretical sectional equilibrium to evaluate the effective flexural secant stiffness. For practical serviceability assessment and to reduce dependence on complex analytical procedures, strain vectors and stiffness matrix components are derived using elasticity coefficients that reflect modulus degradation obtained from numerical analysis. The accuracy of the model is verified through comparison with experimental results, including ultimate flexural capacity and moment–deflection responses. Many crucial parameters were studied, such as the longitudinal reinforcement ratio, type of reinforcement, concrete compressive strength, position of the I-GFRP profile, and rotation of the I-GFRP profile. The results of this study demonstrated that both the longitudinal reinforcement ratio and the rotation of the I-GFRP profile have a significant influence on the ultimate load capacity and deflection behavior. The close agreement between numerical predictions and experimental observations demonstrates the reliability and applicability of the proposed model for structural engineering analysis and design. Full article

Mean atomic bond strain (MABS), based on the globally averaged bond length, has recently emerged as a new strain metric that retains clear physical meaning even as severe atomic neighborhood reconstruction occurs. It has been shown to exhibit a nearly perfect linear relationship with global stress throughout the elastic and plastic deformation in single-crystal face-centered cubic (FCC) metals, contradicting conventional expectations based on nonlinear dislocation activity. Whether this near-linear relationship holds in other materials stands out as an important and intriguing question. In this study, we examine the MABS–stress relationship in representative unary, binary, and ternary metallic glasses (MGs), where neither a crystal structure nor dislocations are present. Large-scale molecular dynamics simulations of uniaxial tensile tests and statistical analysis of millions of atomic bonds are performed. Irrespective of their differing compositions, all the MGs exhibit a persistent near-linear relationship between total MABS (all bonds included) and global stress up to fracture, even in the presence of significant local nonaffine displacements (shear transformation zones and shear bands), with the Pearson correlation coefficient consistently exceeding 0.99. Unlike the nonaffine displacements, the spatial distribution of individual atomic bond strain does not localize under the uniaxial loading. In the MGs containing more than one element, MABS computed for a single bond type may not correlate as linearly with global stress as total MABS. The results demonstrate that the persistent near-linear total MABS–stress relationship over the entire deformation process, recently discovered in single-crystal FCC metals, also applies to MGs despite their vastly different atomic structures. This strengthens the candidacy of total MABS as a universal stress descriptor across materials classes and deformation regimes. With further development and implementation in atomistic simulations and constitutive modeling, the MABS concept has the potential to reshape our understanding of materials mechanics and generate new insights into the design of stronger, tougher, and more thermally and chemically stable materials. Full article