Search Results (177)

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 examines fatigue crack growth behavior in induction-hardened S38C axle steel with a gradient microstructure. High-frequency three-point bending fatigue tests were conducted to evaluate crack growth rates (da/dN) across three depth-defined regions: a hardened layer, a heterogeneous transition zone, and a normalized core. Depth-resolved da/dN–ΔK relationships were established, and Paris Law parameters were extracted. The surface-hardened layer exhibited the lowest crack growth rates and flattest Paris slope, while the transition zone showed notable scatter due to microstructural heterogeneity and residual stress effects. These findings provide experimental insight into the fatigue performance of gradient-structured axle steels and offer guidance for fatigue life prediction and inspection planning. Full article

Magnesium (Mg) alloys are gaining widespread use in the automotive and construction industries for their potential to enhance performance and lower manufacturing costs, making them ideal for lightweight structural applications. However, despite these advantages, extruding Mg alloys remains technically challenging due to their inherently limited formability and the strong crystallographic textures that form during deformation. This study aimed to comprehensively characterize the ductile fracture behavior of ZM51M Mg alloy round bars under various stress states and to improve the reliability of ductile failure predictions through the application and calibration of multiple uncoupled damage criteria. Tensile and compressive tests were conducted on specimens of varying geometries (dogbone, notched R5, shear, uniaxial compression, and plane strain compression specimens) and dimensions, meticulously cut along the extrusion direction of the round bar. These tests encompassed a wide spectrum of stress–strain responses and fracture characteristics, including uniaxial tension, uniaxial compression, and shear-dominated states. An inverse analysis approach, involving iterative numerical simulation coupled with experimental data, was employed to precisely determine fracture strains from the test results. The plastic deformation behavior was accurately modeled using the combined Swift–Voce hardening law. Subsequently, three prominent uncoupled ductile fracture criteria—Rice–Tracey, DF2014, and DF2016—were calibrated against the experimental data. The DF2016 criterion demonstrated superior predictive accuracy, consistently yielding the most accurate fracture strain predictions and significantly outperforming the Rice–Tracey and DF2014 criteria across the tested stress states. The findings of this work provide significant insights for improving the assessment of formability and fracture prediction in Mg alloys. This research directly contributes to overcoming the challenges associated with their inherent formability limitations and complex deformation textures, thereby facilitating more reliable design and broader adoption of Mg alloys in advanced lightweight structural solutions. Full article

The patch loading resistance of slender steel plate girders is a critical factor in the design of launched steel and composite steel–concrete bridges. Traditional design methods enhance patch loading resistance through various stiffening techniques, with contributions typically estimated via code expressions calibrated on experimental data that do not always reflect the complexities of full-scale bridge applications. Finite Element (FE) modeling offers a more realistic alternative, though its practical application is often hindered by modeling uncertainties and nonlinearities. To bridge this gap, this paper introduces an advanced FE modeling approach. It provides a comprehensive description of an FE model that accurately predicts both the load–displacement behavior and the patch loading resistance. The model is benchmarked against a broad set of experimental tests and systematically investigates the effects of key modeling parameters and their interactions—material stress–strain law, boundary condition representation, stiffness of the load introduction area, initial geometric imperfections, and solving algorithms. Key findings demonstrate that a bilinear elastoplastic material model with hardening is sufficient for estimating ultimate resistance, and kinematic constraints can effectively replace rigid transverse stiffeners. The stiffness of the load application zone significantly influences the response, especially in launched bridge scenarios. Initial imperfections notably affect both stiffness and strength, with standard fabrication tolerances offering suitable input values. The modified Riks algorithm is recommended for its efficiency and stability in nonlinear regimens. The proposed methodology advances the state of practice by providing a simple yet reliable FE modeling approach for predicting patch loading resistance in real-world bridge applications, leading to safer and more reliable structural designs. Full article

Analysis of internal pressure failure is a crucial aspect of assessing pipeline integrity. By combining the unified yield criterion with actual burst data, the applicability of different yield criteria is elucidated. Based on the distribution law of burst data, a linear average yield criterion is proposed. The results indicate that the yield function of the linear average yield criterion is a linear expression, and the yield path forms an equilateral non-equiangular inscribed dodecagon within the von Mises circle. For the evaluation of failure pressure, this yield criterion exhibits the highest level of applicability, followed by the ASSY and Tresca yield theories. The linear average yield criterion limits the failure pressure prediction error, with low strain-hardening (0 ≤ n ≤ 0.06) to within 3%. Full article

Traditional laboratory rutting tests are performed at a constant temperature by neglecting pavement temperature variation. The mechanical properties of asphalt are susceptible to temperature variation. This sensitivity to temperature variations significantly influences the performance and durability of asphalt pavements. Following this purpose, a stepwise temperature-controlled rutting test method was proposed to investigate the rutting development of double-layer asphalt pavement (DLAP) under variable temperature. A time-hardening model was developed and employed to evaluate the rutting performance of DLAP under variable temperature. Results indicate that the rutting development of DLAP exhibits a stepwise variation when subjected to variable temperatures. Within a specific constant temperature range, rutting development can be fitted using a power function of load cycles. The rutting deformation of DLAP predominantly occurs at 20 °C; once the temperature exceeds 50 °C, the rutting development accelerates and becomes difficult to stabilize. The time-hardening model effectively captures the rutting development under variable temperature. The predicted values align closely with field values, which demonstrates the model’s feasibility in calculating rutting deformation under variable temperature. Under actual service conditions, the rutting development of DLAP follows a periodic S-shaped growth, yet this trend can still be represented by a power-law function. DLAP exhibits satisfactory durability and structural stability, effectively addressing the challenges posed by traffic loads and high temperatures in test sections. Full article

The Modified Maximum Force Criterion (MMFC) and Marciniak–Kuczynski (MK) models were initially developed to evaluate strain localization in sheet metals. This study investigates their use in predicting the forming limit diagram (FLD) of a tubular material, specifically C1100 pure-copper tubes. To achieve this, uniaxial tensile tests were performed to develop a robust constitutive model, capturing the material’s hardening behavior with a combined Swift–Voce hardening law. A MATLAB code was then developed to theoretically predict the FLD using an enhanced MMFC model, termed MMFC2, alongside the established MK model. These predictions were validated against experimental results from tube expansion tests. Additionally, the theoretical FLDs were integrated into finite element simulations of the tube expansion test to forecast tube bursting behavior. The comparisons reveal that the MMFC2 model’s predictions align more closely with experimental outcomes than those of the MK model, highlighting MMFC2’s superior potential for predicting FLDs in tubular materials. Full article

Through alternating high–low temperature and humid heat tests, six sets of different humidity cycle numbers were applied to Q235B low-carbon steel and Q345B low-alloy steel. Monotonic tensile tests were conducted to compare the differences in monotonic performance degradations. The influence of humidity cycle numbers on the hysteretic and fatigue performance of Q235 steel was investigated through cyclic loading tests. A cyclic constitutive model based on the mixed hardening model was established and validated. The results show that the humid heat environment causes corrosion of the steel, and the degree of corrosion follows a power-law relationship with the number of humid heat cycles. Under monotonic loading, as the number of humid heat cycles increases, the strength and deformation performance of both steels degrade linearly, with Q345 low-alloy steel exhibiting more significant performance deterioration. The corrosion damage induced by the humid heat environment greatly reduces the low-cycle fatigue life of Q235 steel, and the more severe the corrosion, the lower the fatigue life. However, there is no significant effect on the development of the hysteretic curve shape. Under variable amplitude cyclic loading, as the corrosion degree increases, the hysteretic energy dissipation and energy dissipation rate continuously decrease. The two-segment backbone curve considering mass loss rate and the material hardening parameters based on the mixed hardening model can accurately describe the hysteretic characteristics of Q235 low-carbon steel under the humid heat environment. Full article

Soil-structure interface properties play an essential role in geotechnical engineering. The interface shear test is widely used to measure the interface properties. However, in the traditional interface shear test (TIST), distribution of shear stresses along contact surface is not uniform due to boundary effects. Thus, average mechanical response of the whole interface measured by TIST cannot be used to evaluate interface friction properties. In this paper, a novel interface shear apparatus (MIDST) is presented to investigate the shear behaviours of the soil-structure interface. A series of shear tests were conducted on Fujian standard sand-steel interface. Two shear force sensors simultaneously monitor the shear force along the interface: a pre-embedded sensor inside the interface/steel plate (responding to MIDST), while the other outside the interface (responding to TIST). Laboratory test results show that the pre-embedded internal sensor successfully detects the weakening characteristics of the interface, while the external sensor monitors the hardening law. The interface shear strength measured by internal sensor is significantly higher than that monitored by external sensor. A commercial DEM software Version 5.0, Particle Flow Code in Two Dimensions (PFC^2D), is employed to study the soil-structure interaction mechanism, and numerical test results show that the main reasons for the internal and external differences are the uneven shear stress distribution at the soil-structure interface and the boundary effect. In addition, numerical test results agree with the laboratory test results, indicating that the shear behaviours monitored by MIDST are relatively accurate and can provide a reference for engineering design. Full article

The grind-hardening process is capable of generating a martensitic-based hardened layer on the workpiece surface. The production of a hardened layer can significantly improve the application properties of the workpiece. In fact, theoretical research on the wear process of hardened layers is a powerful key to promoting the grind-hardening process, which is the main focus of the current experimental study. For this purpose, the paper carries out the grind-hardening experiment on AISI 1045 steel first by discovering the formation mechanism of the hardened layer. Then, friction and wear experiments are conducted on hardened workpieces to analyze the influence laws of different conditions on the friction coefficient and wear morphology, as well as its profile. On this basis, combined with the Archard wear model, finite element simulations are carried out on the wear process with different friction conditions. The wear depth is effectively predicted. The results show that the wear depth gradually rises with the increase in friction load and frequency. Additionally, considering different friction conditions, the errors between the predictive and experimental values of the wear depth with both average friction coefficient and variable friction coefficient are 4.36–15.22% and 1.57–10.4%, respectively, which validates theoretical research on the wear resistance of the hardened workpiece. Full article

The accurate calibration of snow parameters is necessary to establish an accurate simulation model of snow, which is generally used to study tire–snow interaction. In this paper, an innovative parameter inversion method based on in situ test results is proposed to calibrate the snow parameters, which avoids the damage to the mechanical properties of snow when making test samples using traditional test methods. A coupled Eulerian–Lagrangian (CEL) model of plate loading in snow was established; the sensitivity of snow parameters to the macroscopic load–sinkage relationship was studied; a plate-loading experiment was carried out; and the parameters of snow at the experimental site were inverted. The parameter inversion results from the snow model were verified by the experimental test results of different snow depths and different plate sizes. The results show the following: (1) The material cohesive, angle of friction, and hardening law of snow have great influence on the load–sinkage relationship of snow, the elastic modulus has a great influence on the unloading/reloading stiffness of snow, and the influence of density and Poisson’s ratio on the load–sinkage relationship can be ignored. (2) The correlation coefficient between the inversion result and the matching test data is 0.979, which is 0.304 higher than that of the initial inversion curve. (3) The load–sinkage relationship of snow with different snow depths and plate diameters was simulated by using the model parameter of inversion, and the results were compared with the experimental results. The minimum correlation coefficient was 0.87, indicating that the snow parameter inversion method in this paper can calibrate the snow parameters of the test site accurately. Full article

Studying the factors affecting machining accuracy, surface quality, and machining efficiency in the powerful honing machining process system, analyzing the basic law between various errors and machining quality, exploring the method of evaluating the quality of honing, and improving the machining quality and transmission performance of hardened gears has important engineering application value. Firstly, this paper establishes an effective abrasive grains micro-edge honing quality evaluation model, proposes a method based on the Trapezoidal Fuzzy Analytic Hierarchy Process (Tra-FAHP) and Set Pair Analysis (SPA) to comprehensively evaluate the quality of the honing process, and obtains the influence weights of each factor on the quality of honing. Secondly, the paper analyzes the influence rules of three types of abrasive grain sizes on helix error, tooth pitch error, tooth profile error, surface roughness, and honing efficiency. Finally, the correctness of the established comprehensive evaluation model of honing quality was verified with the threshold method and weights. The research results show that the model can correctly evaluate the quality of hardened gear honing and can be applied to studying the influence of abrasive grain micro-edge honing on machining characteristics. Full article

Shale is a common rock in oil and gas extraction, and the study of its nonlinear mechanical behavior is crucial for the development of engineering techniques such as hydraulic fracturing. This paper establishes a new coupled elastic–plastic damage model based on the second law of thermodynamics, the strain equivalence principle, the non-associated flow rule, and the Drucker–Prager yield criterion. This model is used to describe the mechanical behavior of shale before and after peak strength and has been implemented in ABAQUS via UMAT for numerical computation. The model comprehensively considers the quasi-brittle and anisotropic characteristics of shale, as well as the strength degradation caused by damage during both the elastic and plastic phases. A damage yield function has been established as a criterion for damage occurrence, and the constitutive integration algorithm has been derived using a regression mapping algorithm. Compared with experimental data from La Biche shale in Canada, the theoretical model accurately simulated the stress–strain curves and volumetric–axial strain curves of shale under confining pressures of 5 MPa, 25 MPa, and 50 MPa. When compared with experimental data from shale in Western Hubei and Eastern Chongqing, China, the model precisely fitted the stress–strain curves of shale at pressures of 30 MPa, 50 MPa, and 70 MPa, and at bedding angles of 0°, 22.5°, 45°, and 90°. This proves that the model can effectively predict the failure behavior of shale under different confining pressures and bedding angles. Additionally, a sensitivity analysis has been performed on parameters such as the plastic hardening rate b, damage evolution rate B_ω, weighting factor r, and damage softening parameter a. This research is expected to provide theoretical support for the efficient extraction technologies of shale oil and gas. Full article

As an important civil and military infrastructure, airport runway pavement is faced with threats from cluster munitions, since it is vulnerable to projectile impacts with internal explosions. Aiming at the damage assessment of an island airport runway pavement under impact, this work dealt with discrete modeling of rigid projectile penetration into concrete pavement and the calcareous sand subgrade multi-layer structure. First, the Discrete Element Method (DEM) is introduced to model concrete and calcareous sand granular material features, like cohesive fracture and strain hardening due to compression, with mesoscale constitutive laws governing the normal and shear interactions between adjacent particles. Second, the subsequent DEM simulations of uniaxial and triaxial compression were performed to calibrate the DEM parameters for pavement concrete, as well as subgrade calcareous sand. Prior to the multi-layer structure investigations, penetration into sole concrete or calcareous sand is validated in terms of projectile deceleration and depth of penetration (DOP) with relative error ≤ 5.6% providing a reliable numerical tool for deep penetration damage assessments. Third, projectile penetration into the airport runway structure with concrete pavement and calcareous sand subgrade was evaluated with validated DEM model. Penetration numerical simulations with various projectile weight, pavement concrete thickness as well as striking velocity, were performed to achieve the DOP. Moreover, the back-propagation (BP) neural network proxy model was constructed to predict the airport runway penetration data with good agreement realizing rapid and robust DOP forecasting. Finally, the genetic algorithm was coupled with the proxy model to realize intelligent optimization of pavement penetration, whereby the critical velocity projectile just perforates concrete pavement indicating the severest subsequent munition explosion damage. Full article

This publication deals with the comparative analysis of theoretical and empirical models suitable for predicting forming limit curves in the case of aluminum–magnesium alloys. The Stören–Rice and Hill–Bressan–Williams equations were evaluated and justified by inverse parameter identification. They showed good agreement with the measured strain values. Using the graphical Modified Maximum Force Criterion, it was demonstrated that the Voce hardening law is more suitable than the Swift one for characterizing this group of alloys, but the weighted combination of the two hardening laws is preferable. Full article