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Highlights The outstanding mechanical performance and flowability of unidirectionally arrayed chopped strands (UACSs) give them an advantage in the manufacture of engineering structures with complex geometry. For the application of practical structures, the impact responses and damage evolution of material under low‐velocity impact must be investigated in advance. In this study, UACS laminates and continuous carbon fiber laminates with a stacking sequence of [0/90]4s and a thickness of 2 mm were fabricated for low‐velocity impact tests at 7, 11, 15, and 20 J. The impact responses and postimpact intralaminar damage area were analyzed according to the experimental results, including impact load responses and ultrasound C‐scan inspections. Moreover, to predict the damage evolution of the internal structure, the 3D finite element models were constructed in ABAQUS using a progressive damage model (PDM) through a user‐material subroutine VUMAT. Compared with continuous carbon fiber laminates, the dissipated energy of UACS laminates increases by approximately 10.64% and 57.37% for the 15 and 20 J, respectively. However, the intralaminar damage area of UACS laminates decreased by 29.96% and 28.16% at 15 and 20 J, respectively, since the discontinuous slits in UACS laminates can guide damage paths and suppress damage propagation. The regularly arrayed short fiber reinforced composite was studied. Revealed the low‐velocity impact responses and predicted the damage evolution. UACS and CFRP laminates have comparable impact performance. Illustrated the slits design can suppress the damage to a relatively small area. [ABSTRACT FROM AUTHOR]

Backfilling is a promising measure for controlling surface subsidence in mined-out areas and disposing solid wastes from the mineral processing, there are increasing demands of enhanced toughness and anti-cracking properties of backfill materials to prolong the service life under the complex loads. In this study, polypropylene (PP) fibers were employed to improve performance of backfills, four-point bending and uniaxial compression tests were conducted to investigate the failure process and damage evolution of fiber-reinforced aeolian-sand backfill materials (FABs) using Digital Image Correlation (DIC) and Acoustic Emission (AE) techniques. The results show that the compressive strength tends to decrease with the increasing fiber volume fractions, while the four-point bending strength shows a tendency to increase initially and then decrease, and the optimum volume fraction of PP fiber is 0.6%. At the optimal fiber volume fraction, PP fibers with lengths of 3 mm and 9 mm resulted in a 65.25% and 81.62% increase in the four-point bending strength of FABs, respectively. As indicated by DIC measurements, PP fibers with a length of 9 mm were more effective in controlling the horizontal and vertical displacements of FABs under four-point bending loads than that of 3 mm, and the cracks developed more slowly at the same deflection. In addition, PP fibers with a length of 9 mm have stronger crack extension delay characteristics due to longer effective anchorage distance, as evidenced by more frequent acoustic emission ringing counts and higher cumulative ringing counts. The results of the study may provide a theoretical basis for the application of FABs materials in backfilling. [ABSTRACT FROM AUTHOR]

Creep damage assessment is crucial for ensuring the long‐term reliability of key components operating at high temperatures. However, the existing studies on creep damage are mainly focused on constant loading conditions, while the effect of cyclic loading, which is a common loading mode in practice, remains unclear. In this paper, a series of stress‐controlled cyclic creep tests on the Inconel 718 superalloy were performed to investigate the influence of cyclic loading on creep damage evolution. The ex‐situ microstructural analyses, including fracture surface observations and EBSD measurements, were conducted to reveal the damage mechanisms under cyclic creep conditions. Furthermore, a cavity nucleation and growth model that accounts for the additional cavity closure was developed for the healing effect of cyclic creep damage evolution. The prediction results were consistent with the experimental data of cavity nucleation life and experimental life within a factor of 2. Performing cyclic creep tests under various holding time and stresses.Establishing a cavity nucleation and growth model considering cavity closure.Considering the effect of cyclic loading on creep damage evolution.Revealing the microscopic interactions under cyclic creep conditions. [ABSTRACT FROM AUTHOR]

In order to study the dynamic damage evolution law of tunnel‐lining concrete with non‐through crack under single‐side sulfate attack, a 420‐day sulfate attack concrete test was conducted and the uniaxial compression and acoustic emission (AE) tests were carried out on each corrosion time. The test results showed that the compressive strength of each group can be divided into rising stage and falling stage, and the existence of non‐through crack reduced the compressive strength of concrete specimens and accelerated the corrosion of concrete specimens by sulfate. AE ringing count can be divided into compaction stage, elastic stage, yield stage, and post‐peak stage; the variation patterns of AE varied at different stages. Sulfate attack caused the yield point of concrete to advance. With the increase of corrosion time, microcracks increased gradually, cement mortar was consumed continuously, concrete spalling occurred, the proportion of AE cumulative ringing count Stage II decreased gradually, and the proportion of Stage III increased. Non‐through crack changed the energy storage of Stages II and III and reduced the AE activity of concrete after corrosion. The deeper the crack was, the smaller the average cumulative ringing count was and the lower the AE activity was. AE cumulative ringing counts can be used to characterize the damage evolution of corroded concrete. [ABSTRACT FROM AUTHOR]

The Chaudonneret model cannot fully and effectively characterize the linear correlation between the strain energy density release rate and the number of cycles in the damage evolution stage of low carbon alloy steels under multiaxial non-proportional loading. In order to solve this problem, the fatigue failure process of Q355B is captured by digital image correlation technology, and the factors affecting fatigue failure under multiaxial loading are analyzed in combination with fracture morphology characteristics. Based on the concept of critical plane, a new stress combination form is introduced to reflect the failure factors, and the corresponding damage evolution model is proposed. The model considers the interaction between different stresses and can describe the damage evolution law under non-proportional loading. Compared with different types of life prediction models, the distribution range of life prediction results of the improved model under multiaxial non-proportional loading has a good correlation with the experimental values. [ABSTRACT FROM AUTHOR]

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The damage evolution process of layered rock is influenced by its fine structure, lamination direction, and confining pressure, exhibiting significant anisotropic characteristics. This study focuses on shale as the research object, employing indoor tests and theoretical analysis to define damage variables and initial damage based on ultrasonic wave velocity. This research investigates the damage evolution law of layered rock under varying confining pressures and dip angles. The findings reveal that damage variables defined using transverse wave velocity effectively reflect the damage evolution process. Additionally, confining pressure significantly affects damage evolution, with increasing pressure causing a rightward shift in the damage variable–strain curve and an increase in initial damage. The slab inclination angle also influences damage evolution; samples with 45° and 60° inclinations are more susceptible to damage, with initial damage showing a trend of increasing and then decreasing. To accurately describe the relationship between damage variables and strain during the loading process, this paper establishes a segmented damage evolution equation characterized by wave velocity. Initially, an inverse proportional function is employed to characterize the strain before crack closure. Subsequently, a logistic function represents the curve from crack strain to peak strain. This combined approach provides a comprehensive depiction of the damage evolution. This study underscores the importance of considering confining pressure and laminar inclination in the analysis of rock stability and integrity. These results provide critical insights into the damage evolution characteristics of layered rocks, offering valuable references for engineering safety assessments. [ABSTRACT FROM AUTHOR]

Liquid nitrogen (LN2) fracturing has various advantages, such as low reservoir damage, minimal environmental impact, and excellent permeability. In this study, the cracking pattern and damage evolution characteristics of bedded coal subjected to LN2 fracturing were investigated. The deterioration features of the mechanical parameters and failure mechanisms were examined in a comparable manner using Brazilian splitting tests. Additionally, the damage characteristics of bedded coal during LN2 fracturing were explored. The results indicated that LN2 cooling promoted the development of thermal cracks, consequently reducing the effective bearing capacity of the coal. Randomly distributed thermal cracks actively contributed to macroscopic crack propagation, increasing the proportion of shear cracks and the complexity of the fracture surface. Different bedding angles led to distinct failure modes, significantly impacting the proportion of shear cracks and the fracture surface complexity. Moreover, the bedding planes constantly influenced the propagation direction of the fracturing cracks, resulting in a macroscopic damage zone that expanded preferentially at the weak bedding planes with the borehole at the center. With increasing bedding angles, both the degree and rate of damage of coal decreased sequentially. Consequently, it was feasible to employ LN2 fracturing in low-permeability reservoirs along the bedding planes, facilitating swift and efficient reservoir fracturing. [ABSTRACT FROM AUTHOR]

AbstractMicrowaves have great potential to increase the efficiency of hard rock breakage during mechanical excavation in engineering. This study conducted uniaxial compression tests on granite specimens after microwave irradiation at 4.85 kW. The results demonstrated a linear decrease in uniaxial compressive strength and elastic modulus correlating with increasing irradiation durations. Acoustic emission data indicated increased normalized crack closure stress and decreased normalized crack initiation and damage stress, suggesting complex crack propagation and evolution patterns under microwave influence. 3D Digital Image Correlation revealed that as heating time increased, the macrocrack leading to specimen failure shifted from being load-dominated to involving both load and microwave-induced thermal cracks. A simple four-parameter damage constitutive model for granite (a1, r1, a2, and r2) effectively described the damage evolution under the coupling effect of microwave and uniaxial load. The model accurately characterized the complete stress–strain curves, including both microcrack compaction and post-peak stages, revealing that initial damage escalates with longer heating, though the progression rate decreases. [ABSTRACT FROM AUTHOR]

Highlights Dewetting is one of the most common damage modes in particulate filled polymer composite, which greatly damages the structural integrity of the composite and leads to the deterioration of its mechanical properties. Studying the dewetting evolution process of composite is of great significance for evaluating the meso damage degree of composite and suppressing the development of dewetting damage. This article constructs an axisymmetric cylindrical cell model of a single particle inclusion matrix, derives the interface dewetting evolution process of the model under uniaxial tensile loading condition, and analyzes the influence of model geometric parameters and external loading conditions on the dewetting process. Subsequently, numerical models were constructed at both micro and meso scales, and dynamic tensile calculations were performed to analyze the correlation between the dewetting rate, porosity, and mechanical performance. Finally, a cylindrical cell specimen was designed to observe the interface dewetting evolution under uniaxial tensile conditions, confirming the conclusions of theoretical analysis and numerical simulation. Constructed a theoretical model for the dewetting process of interface. Conducted numerical analysis of dewetting process at both meso and micro scales. Designed interface dewetting experiment and analyzed the dewetting process. [ABSTRACT FROM AUTHOR]

Numerous studies have demonstrated that under low-velocity, low-energy impact conditions, although the surface damage to fiber-reinforced composite laminates may be minimal, significant internal damage can occur. Consequently, a progressive damage finite element model was specifically developed for thermoplastic carbon fiber-reinforced composite laminates subjected to low-speed impact loads, with the objective of analyzing the damage behavior of laminates under impacts of varying energy levels. The model utilizes a three-dimensional Hashin criterion for predicting intralayer damage initiation, with cohesive elements based on bilinear traction–separation law for predicting interlaminar delamination initiation, and incorporates a damage constitutive model based on equivalent displacement to characterize fiber damage evolution, along with the B-K criterion for interlaminar damage evolution. The impact response of laminates at energy levels of 5 J, 10 J, 15 J, 20 J, and 25 J was analyzed through numerical simulation, drop-hammer experiments, and XCT non-destructive testing. The results indicated that the simulation outcomes closely correspond with the experimental findings, with both the predicted peak error and absorbed energy error maintained within a 5% margin, and the trends of the mechanical response curves aligning closely with the experimental data. The damage patterns predicted by the numerical simulations were consistent with the results obtained from XCT scans. The study additionally revealed that the impact damage of the laminates primarily stems from interlaminar delamination and intralayer tensile failure. Initial damage typically presents as internal delamination; hence, enhancing interlaminar bonding performance can significantly augment the overall load-bearing capacity of the laminate. [ABSTRACT FROM AUTHOR]

Thermoplastic composites have a high application demand in aerospace, marine military and other cutting‐edge industry. However, it poses a considerable obstacle in achieving three‐dimensional (3D) thermoplastic composites because of the inadequate infiltration of highly viscous thermoplastic resins. In this paper, high‐toughness Polyetheretherketone (PEEK) resin‐based 3D orthogonal carbon fiber thermoplastic composites were designed and obtained. Low‐velocity impact test was conducted on 3D orthogonal woven composite (3DOWC) under the energy levels of 5 and 10 J, and its performance was compared with that of the 2D unidirectional layup composite (2DULC) and the 2D plain layup composite (2DPLC). The results showed that 3DOWC possessed superior elastic energy absorption capacity and less damage morphology compared to 2D composites. 3DOWC had the highest contact force value of 2420.25 N at 10 J, which is 36.83% higher than that of 2DPLC. Furthermore, a finite element model in multi‐scale was established to investigate the damage evolution and failure mechanism of the 3D orthogonal woven CF/PEEK composites. The damage morphology observed in both experimental and numerical findings demonstrated that the matrix shedding, while the yarn fractured on the nonimpact side beneath the impact point. Additionally, enhancing the tensile strength of the yarn in the bottom layer can lead to further improvement in impact resistance. This work provides an innovative method for manufacturing 3D thermoplastic composites and lays the foundation for the impact simulation analysis of such composites. Highlights: A novel approach was introduced for fabricating 3D carbon fiber/PEEK composites, which exhibits remarkable resistance to impact.A comprehensive investigation was conducted to evaluate the impact properties of 3D thermoplastic composite compared to 2D composite.A finite element model in multi‐scale including failure criteria was established to simulate the damage evolution. [ABSTRACT FROM AUTHOR]

To study the damage and acoustic emission (AE) energy evolution of basalt under high temperature, a series of tests under uniaxial stress are carried out on basalt heated at 25 °C, 200 °C, 400 °C, 600 °C, 800 °C and 1000 °C. Through the comprehensive analysis of AE parameters such as absolute energy and amplitude, the AE characteristics and damage evolution laws of basalt were explored. The results show that high temperature has a significant effect on the characteristics of rock stress–strain curve. With the increase of temperature, the compaction stage of the curve becomes longer, the plasticity increases, and the peak strength of basalt decreases. The higher the heat treatment temperature, the faster the strength decreases, and the strength decreases by 63.91% at 1000 °C. The AE localization points converge from the dispersed state to the aggregated state. With the increase of temperature, the period of convergent nucleation of the AE localization sites is advanced, high amplitude AE signals shifted from a concentrated distribution near the peak stress to a discrete distribution throughout the entire process. The heat treatment of the rock has an additive effect on the burstiness. 600–800 °C can be used as the threshold temperature of basalt to transform from brittle failure to plastic failure. The high temperature effect is responsible for the transition of the AE cumulative absolute energy at 400–600 °C. The influence of high temperature on damage evolution is discussed. The initial damage increases exponentially after 800 °C. With the increase of temperature, the evolution rate of damage variable becomes faster and gradually changes from linear to nonlinear. [ABSTRACT FROM AUTHOR]

This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading. The calibration of four typical failure parameters for 40CrMnSiB steel was conducted through experiments and subsequently applied to simulations. The numerical simulation results employing the four failure criteria were compared with the differences and similarities observed in freeze-recovery tests and ultra-high-speed tests. This analysis addressed the critical issue of determining failure criteria for the fracture of a metal shell under internal explosive loads. Building upon this foundation, the damage parameter Dc, linked to the cumulative crack density, was defined based on the evolution characteristics of a substantial number of cracks. The relationship between the damage parameter and crack velocity over time was established, and the influence of the internal central pressure on the damage parameter and crack velocity was investigated. Variations in the fracture modes were found under different failure criteria, with the principal strain failure criterion proving to be the most effective for simulating 3D crack propagation in a pure shear fracture mode. Through statistical analysis of the shell penetration fracture radius data, it was determined that the fracture radius remained essentially constant during the crack evolution process and could be considered a constant. The propagation velocity of axial cracks ranged between 5300 m/s and 12600 m/s, surpassing the Rayleigh wave velocity of the shell material and decreasing linearly with time. The increase in shell damage exhibited an initial rapid phase, followed by deceleration, demonstrating accelerated damage during the propagation stage of the blast wave and decelerated damage after the arrival of the rarefaction wave. This study provides an effective approach for investigating crack propagation and damage evolution. The derived crack propagation and damage evolution law serves as a valuable reference for the development of crack velocity theory and the construction of shell damage evolution modes. [ABSTRACT FROM AUTHOR]

Phosphogypsum backfill technology is an important way of backfill mining. However, phosphogypsum has problems such as poor water resistance and low strength. Therefore, in this study, phosphogypsum and carbide slag (CS) were mixed to form the phosphogypsum backfill (PB). The effects of the CS content on the workability, mechanical properties, and microstructure of PB were studied by means of pH value, bleeding rate, fluidity, strength, water resistance, SEM, and XRD. The results showed that the incorporation of CS significantly improved the working performance. The softening coefficient initially climbed and subsequently declined. Peak stress and MOE of PB showed a trend of rise-fall, reaching the peak when CS content was 10%. The damage evolution process of PB was revealed. The process of energy dissipation of PB during uniaxial compression showed a law of increasing and then decreasing with increasing CS dosage. The test group composed of 90% phosphogypsum and 10% CS was the best experimental scheme. These results were hoped to provide guidance for the comprehensive utilization of phosphogypsum and CS and the theoretical basis for the application of PB in backfill mining. [ABSTRACT FROM AUTHOR]

Highlights It is important to study damage evolution as well as failure of carbon fiber reinforced polymer (CFRP) plates bolted joints. Therefore, the quasi‐static tensile test on single‐lap and double‐lap CFRP plates bolted joints was conducted. Meanwhile, the tensile strength prediction model for titanium alloy bolted joint of CFRP plates was established based on the improved 3D Hashin failure criterion, then a theoretical model was proposed to accurately predict the load distributions and tilt angle of bolted joints. Thus, the load–displacement curves were divided into four stages, and load distributions at different stage points as well as the relationship between tilt angle of bolt and load variation were obtained. The damage evolution of single‐lap and double‐lap at different stage points was analyzed respectively, and failure mechanisms were revealed based on load distribution. The results show that the ultimate failure of single‐lap is caused by the intrusion of bolt head into CFRP plates, while double‐lap is caused by the compression deformation of central plate. The numerical simulation works are in high agreement with the experimental results. Calculate the load distribution at single‐lap and double‐lap bolted joints. Obtain the relationship between bolts tilt angle and load variation. Analysis of damage evolution in bolt‐hole wall of carbon fiber reinforced polymer (CFRP) plates. Using loads to reveal the failure mechanisms of single‐lap and double‐lap bolted joints of CFRP plates. [ABSTRACT FROM AUTHOR]

This research examines the microstructure, deformation and hysteresis curves of corn kernels with different water content, to quantify the quasi-brittle mechanical properties of corn kernels. A significant finding was that with the increasing water content from 10 to 30%, the maximum load that corn kernels can bear increases and then decreases gradually. The bearing capacity of corn grain with 14% moisture content was the highest. The limit load is 160 N. The relationship between load and fatigue life of corn kernel was obtained by a compressive fatigue test. The fatigue load–fatigue life curve of corn grains was established. It was concluded that the higher the load, the shorter the fatigue life, and with the increase in water content, the fatigue life of corn kernels would gradually decrease. This is because with the increase in water content, first, the linear elastic stage of corn grain gradually decreases, and the nonlinear stage gradually increases. The second is the transition from brittle fracture to quasi-brittle fracture, and the load required to produce damage inside the grain is gradually reduced. Through damage theory and Micro-CT test, the nonlinearity of damage accumulation in corn kernels was proved. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) can monitor and evaluate the cracking situations of hydraulic structures for it is real-time and non-destructive. However, a current challenge of this approach is to accurately identify the various stages during the cracking process. The innovation of this paper lies in the application of AE data in analyzing the stage characteristics during the whole process of hydraulic concrete fracture. First, the slope changing of the cumulative ringing count curve was used to determine the cracking stages of hydraulic concrete. Second, the function of inter-event times (denoted as F-function) was used to further investigate the AE characteristics proximity to the final fracture. Last, the spatial-temporal-energy evolution of cracks was studied. The results show that: (1) The whole process of hydraulic concrete failure shows an obvious stage characteristic from the perspective of AE feature and it can be distinguished to five stages by the slope change of the cumulative ringing count curve; (2) The F-function can be used to identify the last two cracking stages, and it is capable of early warning the macroscopic cracking in ahead of b-value; (3) The spatial-temporal-energy distribution of cracks helps to better understanding the generation and evolution for cracks inside hydraulic concrete. [ABSTRACT FROM AUTHOR]

This paper is concerned with environmental corrosion during service of load‐bearing aluminum alloys fabricated by additive manufacturing (AM) with a focus on damage evolution characterization and identification of dominated failure mechanisms of pre‐corroded selective laser melted aluminum alloy. An experimental strategy for analysis of the damage and failure process is presented, combining 3D surface measurement, 3D digital image correlation, and scanning electron microscopy, to provide a multi‐source experimental characterization of corrosion morphology, strain field evolution, and fracture morphology. Statistics and machine learning methods were employed to process the measured multi‐source experimental data, showing that local average roughness has a strong influence on macro‐crack initiation position. The analysis focuses on four primary types of fatigue micro‐crack initiation, namely, internal defect, diffuse corrosion, corrosion micro‐pit, and corrosion jut; internal defect and diffuse corrosion are unique features for powder bed fusion (PBF) AlSi10Mg. The micro‐crack initiation mechanisms for all four types are (i) local stress concentrations due to adjacent material micro‐structural defects, (ii) interaction of underlying alloy microstructure and corrosion‐induced stress/strain, and (iii) local stress/strain concentration at corrosion micro‐pit and jut, respectively. Highlights: Fatigue damage and failure mechanism of pre‐corroded SLM AlSi10Mg were investigated.Experimental strategy was proposed to provide associated multi‐source information.Effect of corrosion morphology characteristics on macro‐crack initiation was evaluated.Main fatigue micro‐crack initiation forms and corresponding mechanisms were analyzed. [ABSTRACT FROM AUTHOR]

Recently developed multi-scale fiber (i.e., CaCO3 whisker, polyvinyl alcohol (PVA) fiber, and steel fiber) reinforced rubberized concrete exhibits excellent mechanical properties and spalling resistance at high temperatures. Measurement of macro properties such as strength and Young's modulus cannot reveal and characterize damage mechanisms, particularly those relating to the multi-scale fiber strengthening effect. In this study, acoustic emission (AE) technology is applied to investigate the impact of multi-scale fiber on the damage evolution of rubberized concrete exposed to high temperatures, under the uniaxial compression and tension loading processes. The mechanical properties, AE event location, peak frequency, b-value, the ratio of rise time to amplitude (RA), average frequency (AF) values, and AE energy of specimens are investigated. The results show that the number of events observed using AE gradually increases as the loading progresses. The crumb rubber and fibers inhibit the generation and development of the cracks. It is concluded that both the peak frequency and b-value reflect the extension process of cracks. As the cracks develop from the micro scale to the macro scale, the peak frequency tends to be distributed in a lower frequency range, and the b-value decreases gradually. At the peak stress point, the AE energy increases rapidly and the b-value decreases. The specimens without multi-scale fibers exhibit brittle failure, while the specimens with fibers exhibit ductile failure. In addition, adding multi-scale fibers and crumb rubber increases the peak frequency in the medium and high frequency ranges, indicating a positive effect on inhibiting crack development. After being subjected to high temperatures, the maximum and minimum b-values decrease, reflecting an increase in the number of initial cracks due to thermal damage. Meanwhile, the RA and AF values are used to classify tensile and shear cracks. The specimens fracture with more shear cracks under compression, and there are more tensile cracks in specimens with multi-scale fibers under tension. [ABSTRACT FROM AUTHOR]

Sheet metal formation plays a cost-effective and significant role in the fabrication of automobile components. Typically, a forming limit diagram (FLD) is used to determine the strain limit of the material fracture during hot forming. In this study, the Erichsen cupping test is conducted on an Al(7075) sheet at 300, 350, 400, and 450 °C to determine the FLD. The results demonstrate the displacement increases with increasing temperature and load, and it is decreased at 450 °C. Finite element analysis (FEA) of the Erichsen cupping test of the Al sheet is performed with the damage theory using ABAQUS software, and the results are compared with the experimental results. To minimize errors in the Finite Element Analysis (FEA), simulations were conducted by applying the fracture energy value ( G f ). It was observed that the displacement increased in the load–displacement curve as the fracture energy value ( G f ) increased at all temperature values. Additionally, as the G f value increased with temperature, the energy absorption capacity until fracture also increased. [ABSTRACT FROM AUTHOR]

This paper significantly extends investigations into internal damping ratios in both undamaged and damaged conditions for normal-strength concretes (NSCs) and high-strength concretes (HSCs). This study examines concretes with compressive strengths ranging from 42 to 83 MPa. Cyclic loads were applied using a servo-controlled hydraulic testing machine, and for each cyclic step, the dynamic elastic modulus ( E d ) and internal damping ratio (ξ) were determined through acoustic tests. The results show that the normal-strength concretes ( f c = 42 MPa) exhibited an undamaged internal damping ratio of ξ = 0.5 % , reaching a maximum of ξ = 2.5 % at a damage index of 0.8. Conversely, the high-strength concrete mixtures ( f c = 83 MPa) showed an undamaged internal damping ratio of ξ = 0.29 % , with a peak value of ξ = 0.93 % at a damage index of 0.32. The initial internal damping values are influenced by porosity and transition zones, which affect the material behavior under cyclic loads. Progressive damage leads to increased Coulomb damping due the cracking process. Few studies have quantified and comprehended the internal damping ratio under cyclic loading-induced damage, and this research advances our understanding of NSC and HSC behavior under dynamic excitation and damage evolution, especially in impact scenarios. [ABSTRACT FROM AUTHOR]

Depleted gas reservoirs are important natural gas storage media, thus research on the mechanical properties and damage evolution of reservoir rocks under alternating load conditions has significant practical implications for seal integrity studies. This paper conducted multi-level cyclic loading triaxial compression experiments on medium-porosity medium-permeability sandstone under different confining pressures and used acoustic emission (AE) instruments to detect the AE characteristics during the experiment, analyzing the mechanical characteristics, AE, and damage evolution characteristics. The experimental results show that after cyclic loading, the peak strength of sandstone increased by 14–17%. With the increase in the upper limit stress of cyclic loading, the elastic modulus showed a trend of first increasing and then gradually decreasing. The damage variable of rock samples rose with a rise in the upper limit stress of cyclic loading and confining pressure, and the rock damage was mostly localized at the peak stress. The AE b-value increased generally as confining pressure increased, showing that fractures occurred quicker and more unevenly at lower confining pressures. The distribution of RA-AF values shows that a sudden increase in stress causes the initiation and expansion of cracks in medium-permeability sandstone, and that tensile and shear cracks form continuously during the cyclic loading process, with shear cracks developing more pronounced. This research can provide some theoretical guidance for the long-term stable operation and pressure enhancement expansion of depleted gas reservoir storage facilities. [ABSTRACT FROM AUTHOR]

Abstract Backfilling is a promising measure for controlling surface subsidence in mined-out areas and disposing solid wastes from the mineral processing, there are increasing demands of enhanced toughness and anti-cracking properties of backfill materials to prolong the service life under the complex loads. In this study, polypropylene (PP) fibers were employed to improve performance of backfills, four-point bending and uniaxial compression tests were conducted to investigate the failure process and damage evolution of fiber-reinforced aeolian-sand backfill materials (FABs) using Digital Image Correlation (DIC) and Acoustic Emission (AE) techniques. The results show that the compressive strength tends to decrease with the increasing fiber volume fractions, while the four-point bending strength shows a tendency to increase initially and then decrease, and the optimum volume fraction of PP fiber is 0.6%. At the optimal fiber volume fraction, PP fibers with lengths of 3 mm and 9 mm resulted in a 65.25% and 81.62% increase in the four-point bending strength of FABs, respectively. As indicated by DIC measurements, PP fibers with a length of 9 mm were more effective in controlling the horizontal and vertical displacements of FABs under four-point bending loads than that of 3 mm, and the cracks developed more slowly at the same deflection. In addition, PP fibers with a length of 9 mm have stronger crack extension delay characteristics due to longer effective anchorage distance, as evidenced by more frequent acoustic emission ringing counts and higher cumulative ringing counts. The results of the study may provide a theoretical basis for the application of FABs materials in backfilling.

An in-depth understanding of the mechanical properties and damage and fracture mechanism of selected rocks in a diversion tunnel plays an important role in promoting the efficient construction and safety of rock blasting excavation in a diversion tunnel. To study the mechanical properties and damage evolution characteristics of selected rocks in diversion tunnels under uniaxial loading, the uniaxial compression and uniaxial splitting tests of granite and tuff were carried out. In terms of mechanical properties, the evolution characteristics of complete stress-strain curves, instantaneous modulus-strain curves, and input energy density-strain curves were analyzed. In the aspect of damage characteristics, the macroscopic and mesoscopic failure modes were analyzed and the damage fracture mechanism was revealed. Compression-shear failure mainly occurred in granite and tuff under uniaxial compression, showing the characteristics of elastic-brittle fracture failure. Both granite and tuff showed a failure mode of coexistence of “compression-shear failure zone at the loading ends” and “tension-shear failure zone in the middle” under uniaxial splitting. The compression-shear fracture of granite was relatively smooth, and the matrix and mineral particles produced fine particles due to friction in the process of shear slip. The compression-shear fracture of tuff was relatively rough and the characteristics of shear slip were not prominent enough. The fracture failure of granite and tuff was mainly caused by the common fracture of rock matrix and mineral particles. Based on the Lemaitre equivalent strain principle, the pre-peak-post-peak two-stage damage constitutive model established by Weibull statistical distribution theory can accurately describe the static stress-strain relationships of granite and tuff under uniaxial compression.

The mechanical behaviors of hybrid metal–composite joints with different protrusion densities were investigated by combining numerical and experimental methods. High-fidelity finite element models that considered the failure modes of all components were developed, and specimens based on metal additive manufacturing technology were tested under quasi-static tensile load to verify the numerical calculations. The results showed that the load capacity and the dominant fracture mode of joints were significantly affected by the metal protrusion density. The failure mechanisms of joints under different protrusion conditions exhibited a clear difference, which proved the possibility of an optimal and functional joint design. [ABSTRACT FROM AUTHOR]

Characterizing the fatigue behavior of cement-stabilized aggregates (CSAs) is essential to semirigid base asphalt pavement design. However, the relevant research is relatively limited and retains significant challenges. Therefore, fatigue tests subjected to multilevel loads were designed, and a mechanical damage evolution rule was proposed to describe the CSA's damage behavior better. Four-point bending fatigue tests were conducted following the designed loading steps composing different cyclic stress levels and frequency combinations. The damage evolution patterns in sequential and disorder loading cases, together with the plastic strain accumulation trends, were analyzed to uncover the factors influencing CSA's damage evolution. It was found that the general damage evolution of CSA exhibited a three-stage pattern, and it was affected by the cyclic stress level, loading sequence, and history of plastic and damage evolution. Remarkably, loading frequency appeared to have a negligible impact. Plastic strain and damage evolution demonstrated congruent evolution trends in most cases; however, they differed in disorderly loading. To address these, a new damage evolution rule was proposed based on the continuum damage mechanics and driven by the equivalent plastic strain rate. The damage dissipation rate was introduced to characterize the impact of effective stress level, and the damage variable and plastic strain path were also included in the proposed rule to reflect the effect of loading or damage history. The comparison results between the fitted and measured damage evolution curves validated the effectiveness in characterizing the fatigue damage behaviors of CSA when subjected to multilevel loads. Furthermore, the proposed damage evolution rule was also employed to model the damage curves of CSA's uniaxial and indirect tensile fatigue tests with single-level loads. The commendable agreement between the fitting and experimental results confirmed the validity of the proposed rule and showed its broad applicability under different fatigue loading forms. [ABSTRACT FROM AUTHOR]

Ceramic matrix composites (CMCs) have been widely used in aerospace thermal-structures due to their excellent high-temperature performance. It is essential to understand the damage evolution of CMCs. However, in previous research work, the effect of thermal stress induced damage during CMCs fabrication on tensile response was often ignored. A damage evolution model that considers axial and radial thermal stresses to predict tensile response of unidirectional ceramic matrix composites was proposed in this study. The average relative errors between the current prediction and experimental data in the literature were calculated as 1.64 % and 1.91 %, validating this approach. Meantime, the damage evolution laws of interface debonding and the critical stress of matrix cracking in the Budiansky–Hutchinson–Evans (BHE) model were corrected to satisfy the discontinuous interfacial shear stress. According to the experimental data, the current model predicted critical stresses of matrix cracking better than the BHE model, with error rate reductions of 6.52 % and 15.38 %. [ABSTRACT FROM AUTHOR]

Understanding the damage evolution of thermal barrier coatings (TBCs) is crucial for optimizing TBCs systems and predicting service lifetime. This study investigates the correlation between mechanical properties and the thermal cycle lifetime of TBCs with conventional air plasma sprayed (APS) and micro-agglomerated particles embedded (EMAP) plasma sprayed structures, utilizing the Gd 2 Zr 2 O 7 (GZO) and GSc 0.075 Ce 0.3 Z (GSCZ) material systems. The damage evolution and cracking behavior of TBCs with varying material compositions and coating structures are evaluated using a combination of three-point bending tests and digital image correlation (DIC) techniques. Experimental results demonstrate that the thermal cycling lifetime of conventional APS TBCs correlates positively with the fracture toughness of the ceramic layer. Specifically, the conventional APS GSCZ coating with a fracture toughness of 1.12 MPa/m1/2 and the APS GZO coating with a fracture toughness of 0.97 MPa/m1/2 exhibit lifetimes of 34 cycles and 31 cycles, respectively. Moreover, the EMAP structural design exhibits notable advantages in enhancing the thermal cycle lifetime of TBCs across all material systems. DIC results confirm that strain accumulation during interface cracking of EMAP TBCs is effectively mitigated compared to conventional APS TBCs. The loose and porous characteristics of this structure significantly improve the compliance and interface fracture toughness of the TBC system, thereby alleviating TBC failure dominated by interface cracking. [ABSTRACT FROM AUTHOR]

Xiyu conglomerate, widely distributed in the Xinjiang province of China, plays a crucial role in tunnel construction given its mechanical properties under freeze–thaw cycles. Composed mainly of gravel and cementing material, the heterogeneity in the mechanical properties of Xiyu conglomerate results in a damage evolution mechanism under freeze–thaw cycles distinct from that of common rocks. In accordance with the local climatic conditions, this study conducted instantaneous uniaxial monotonic loading and cyclic loading–unloading tests on Xiyu conglomerate specimens with varying freeze–thaw cycle numbers. The relationship between fundamental physical–mechanical properties of Xiyu conglomerate (porosity, P-wave velocity, uniaxial compressive strength, elastic modulus, etc.) and the number of freeze–thaw cycles was analyzed. Deformation characteristics and energy evolution patterns under cyclic loading–unloading for different freeze–thaw cycle numbers were investigated. Computed tomography (CT) scanning experiments were employed to analyze the crack propagation mechanism of Xiyu conglomerate specimens under freeze–thaw damage conditions. In response to observed anomalies in Xiyu conglomerate, our study developed a novel damage evolution model, integrating experimental insights to precisely quantify the combined impacts of freeze–thaw cycles and cyclic loading–unloading. This model not only reflects the unique characteristics of Xiyu conglomerate but also offers new theoretical perspectives on understanding its degradation process. The findings of this research contribute theoretical support to tunnel construction projects in the Xinjiang region of China. Highlights: Research reveals how Xiyu conglomerates respond to natural freeze-thaw cycles. Analyzing Xiyu conglomerate deformation and energy during freeze-thaw and cyclic loading. Developing a dissipated energy based freeze-thaw damage evolution model. Using CT scans to explore freeze-thaw damage mechanisms of inhomogeneous Xiyu conglomerate. [ABSTRACT FROM AUTHOR]

To study the deformation failure and damage evolution law of weathered granite (WG) under different confining pressures, triaxial compression simultaneous acoustic emission (AE) tests were conducted on WG, and the mechanical and AE parameter characteristics of WG were obtained. It is shown that with the increase of confining pressure, the strength and modulus of elasticity of WG increase, and the failure pattern evolves from splitting failure to shear failure. Using the Mohr-Coulomb criterion, the cohesion c of WG is calculated to be 7.03 MPa, and the angle of internal friction φ is 61.95°. Analysing the AE peak frequency and energy at the characteristic points of the differential stress-axial strain curves, it is evident that the confining pressure limits crack evolution. The fractal characteristics of the WG AE ringing counts at each confining pressure are good, and the correlations between their ln r-ln C(r) curves and the fitted curves are all above 0.90. The WG at each confining pressure showed an increasing growth rate in the values of the damage variables and a rapid and substantial decrease in the fractal dimension before failure occurred. The study's results can provide a theoretical basis for the stability analysis of the WG surrounding rock. [ABSTRACT FROM AUTHOR]

Aiming at effectively utilizing recycled coarse aggregate (RCA) in sustainable construction, it is necessary to study the internal damage evolution of steel fiber–reinforced recycled-aggregate concrete (SFRAC) under dynamic tensile loads and the reinforced mechanism of steel fiber. The influences of the steel fiber content, the recycled-aggregate replacement ratio, and the loading rate on the mechanical properties and dynamic damage of SFRAC were studied using the Brazilian disc splitting test and acoustic emission (AE) technology. Then, the mechanism of crack evolution was investigated by means of the parameter analysis method. The results indicate that the existence of RCA makes the mechanical properties of recycled-aggregate concrete worse than those of normal concrete and weakens the strain rate effect of splitting tensile strength, whereas this negative influence can effectively be improved by steel fiber. The preferable steel fiber contents obtained from the splitting tensile strength and peak displacement are 1.0% and 1.5%, and under these conditions, the SFRAC replaced by 30% RCA has a mechanical performance superior to that of normal concrete. It is also found that the damage degree and energy absorbing capacity of SFRAC can be identified by analyzing the ring and energy counts of the AE signal. Furthermore, the evolution of the crack pattern of SFRAC under dynamic axial tensile load is well reflected by the rise angle and average frequency. Increased steel fiber content and recycled-aggregate replacement ratio can change the failure mode to a complex tensile-shear mixed failure, and the shear crack gradually becomes the main crack with increasing loading rates. Practical Applications: The public environment crisis from the greenhouse effect led to a series of measures from all industries worldwide. The widespread use of concrete has brought with it serious environmental and energy-saving problems. The construction industry preliminarily attempts to replace natural aggregate by recycled aggregate obtained by crushing construction solid waste in green low-carbon buildings, which shows considerable carbon sequestration and emission reduction. However, recycled aggregate has poor mechanical properties such as low strength and high porosity. When participating in concrete configuration, this defect seriously affects the strength of the material and limits its wide application in construction engineering. For a component with strength requirements or special purposes, fiber can be adopted to improve the mechanical properties of recycled-aggregate concrete. This study examines the damage process of fiber-reinforced recycled-aggregate concrete with the microscopic method and proposes a satisfactory mix proportion. Naturally, these analysis methods require more time and effort than a basic macroscopic analysis. Moreover, proper research on the mechanism of damage evolution under dynamic loading is crucial. [ABSTRACT FROM AUTHOR]

Abstract To address the issue of roadway support failure in narrow coal pillars under dual-lane layout, this study takes the 4309 working face of Changping Coal Mine as the engineering background and employs theoretical calculations, numerical simulations, and on-site monitoring to investigate the instability mechanisms of narrow coal pillars under dual-lane conditions and to optimize technical solutions. The results indicate that the internal stress distribution within the coal pillar is influenced by the advanced support stress, and as the working face advances, the gradually increasing advanced support pressure causes the vertical stress peak within the coal pillar to shift away from the goaf area. Computational analysis reveals that the vertical stress in the top region of a 6 m narrow coal pillar is 38% higher than that in the bottom region, with an average stress of 16 MPa in the coal pillar. The asymmetric high-level stress concentration within the coal pillar significantly affects its stability. A UDEC (Universal Distinct Element Code) model was established to compare four simulation schemes with cut-off angles of 0°, 5°, 10°, and 15°. Based on the analysis of damage parameters and fracture distribution in the narrow coal pillar roadway, it was concluded that the stability is best when the cut-off angle is 10°. The dense drilling cut-off unloading technology was applied to the 4309 working face of the Changping Mine based on the aforementioned research. On-site monitoring results show that the relative deformation of the roof and bottom plates and the two sides of the test section were controlled within 267 mm and 198 mm, respectively, effectively resolving the deformation and instability issues of the narrow coal pillars.

The exploitation of shale gas is promising due to depletion of the conventional energy and intensification of the greenhouse effect. In this paper, we proposed a heat-fluid-solid coupling damage model of supercritical CO2 (SC-CO2) compound fracturing which is expected to be an efficient and environmentally friendly way to develop shale gas. The coupling model is solved by the finite element method, and the results are in good agreement with the analytical solutions and fracturing experiments. Based on this model, the fracture propagation characteristics at the two stages of compound fracturing are studied and the influence of pressurization rate, in situ stress, bedding angle, and other factors are considered. The results show that at the SC-CO2 fracturing stage, a lower pressurization rate is conducive to formation of the branches around main fractures, while a higher pressurization rate inhibits formation of the branches around main fractures and promotes formation of the main fractures. Both bedding and in situ stress play a dominant role in the fracture propagation. When the in situ stress ratio (σx/σy) is 1, the presence of bedding can reduce the initiation pressure and failure pressure. Nevertheless, it will cause the fracture to propagate along the bedding direction, reducing the fracture complexity. In rocks without bedding, hydraulic fracturing has the lengthening and widening effects for SC-CO2 induced fracture. In shale, fractures induced at the hydraulic fracturing stage are more likely to be dominated by in situ stresses and have a shorter reorientation radius. Therefore, fracture branches propagating along the maximum principal stress direction may be generated around the main fractures induced by SC-CO2 at the hydraulic fracturing stage. When the branches converge with the main fractures, fracture zones are easily formed, and thus the fracture complexity and damage area can be significantly increased. The results are instructive for the design and application of SC-CO2 compound fracturing.

Abstract To investigate the characteristics of destabilization damage in coal-rock complexes. Mechanical property tests were conducted on coal, rock, and their complexes. An infrared thermal camera was employed to real-time monitor the infrared (IR) radiation response signals during the destabilization damage process. A numerical model of coal-rock destabilization damage was developed, and its validity was verified. Deformed stress fields and displacement contours were obtained during the destabilization damage process. Upon destabilization, numerous cracks form at the base of the “coal” section, extending towards the interface, resulting in the formation of a wave-like deformation region. The differentiation in infrared thermal images is more pronounced in the “coal” section compared to the “rock” section. A high-stress region is evident at the interface, resulting in an area of high stress differentials. However, the bottom of the “coal” section also exhibits a region with high stress differentials and a more pronounced tendency towards destabilization damage. Displacement contours revealed that numerous units at the bottom of the “coal” section had slipped and misaligned, leading to the accumulation of damage and an elevation in the local damage level. It is a crucial factor contributing to the notable phenomenon of IR thermal image differentiation.

The damage evolution and failure process of pre-corroded additive manufacturing AlSi10Mg through in-situ tensile experiments under an optical microscope and micro-scale digital image correlation（μ-DIC） were investigates . Combining the microscopic deformation field evolution，material microstructure，three-dimensional corrosion morphology and fracture microscopic morphology to analyze the initiation and propagation of micro-cracks in pre-corroded AlSi10Mg. The results show that the stress concentration around the corrosion pits and subsurface defects（caused by the additive manufacturing process） leads to the initiation of micro-cracks. There are multiple micro-cracks initiating at the same time，and the propagation and coalescence of micro-cracks originated from the key damage regions dominate the final failure of the specimen. Material micro-structure and corrosion morphology have an important influence on crack propagation.

Bedding structure affects the mechanical properties and stability of engineering rock masses. To elucidate the influence of bedding angle on rock deformation and damage process, longitudinal wave velocity tests and uniaxial compression tests were performed on yellow sandstone at bedding angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Furthermore, the influence of the bedding angle on the peak strength, elastic modulus, and failure mode was analyzed. Initial bedding damage and load damage were characterized based on the degradation degree of elastic modulus and evolution characteristics of dissipative energy; moreover, the entire evolution process of coupled layer–load damage was simulated using the logistic function. The influence of the bedding angle on the damage evolution law of yellow sandstone was discussed, and a piecewise constitutive model for simulating the entire deformation process of uniaxial compression was established, combined with the damage mechanics and effective medium theories. The results reveal that with increasing bedding angle, longitudinal wave velocity increases gradually, peak strength and elastic modulus decrease first, then increase, and then decrease, and anisotropy is obvious. The failure mode is closely related to the bedding dip angle. When the dip angle ranges from 0° to 60°, splinter-type tensile failure occurs mainly through the weak side of shear bedding. Moreover, when the dip angle is 75° and 90°, shear slip and splinter tensile failure occur along the weak side of the bedding. The damage evolution curve based on dissipative energy can be divided into four processes: initially undamaged, damage initiation, damage acceleration, and damage deceleration termination. A theoretical damage model constructed using the logistic function can effectively simulate and predict the entire damage evolution process. The ratio of maximum value to minimum value of initial bedding damage is approximately 1.41, indicating that bedding angle substantially affects the initial damage. The piecewise constitutive model can describe the entire stress–strain process of layered yellow sandstone under uniaxial compression, and the theoretical model curves agree well with experimental data. Parameters a and r represent the initial damage degree and damage evolution rate, respectively. Larger a values typically correspond to a lower initial damage degree and higher peak strength. The larger r is, the faster the damage variable develops and the greater the maximum damage evolution rate is. Thus, the theoretical curve shape of the constructed constitutive model is determined by parameters a and r.

To address the issue of roadway support failure in narrow coal pillars under dual-lane layout, this study takes the 4309 working face of Changping Coal Mine as the engineering background and employs theoretical calculations, numerical simulations, and on-site monitoring to investigate the instability mechanisms of narrow coal pillars under dual-lane conditions and to optimize technical solutions. The results indicate that the internal stress distribution within the coal pillar is influenced by the advanced support stress, and as the working face advances, the gradually increasing advanced support pressure causes the vertical stress peak within the coal pillar to shift away from the goaf area. Computational analysis reveals that the vertical stress in the top region of a 6 m narrow coal pillar is 38% higher than that in the bottom region, with an average stress of 16 MPa in the coal pillar. The asymmetric high-level stress concentration within the coal pillar significantly affects its stability. A UDEC (Universal Distinct Element Code) model was established to compare four simulation schemes with cut-off angles of 0°, 5°, 10°, and 15°. Based on the analysis of damage parameters and fracture distribution in the narrow coal pillar roadway, it was concluded that the stability is best when the cut-off angle is 10°. The dense drilling cut-off unloading technology was applied to the 4309 working face of the Changping Mine based on the aforementioned research. On-site monitoring results show that the relative deformation of the roof and bottom plates and the two sides of the test section were controlled within 267 mm and 198 mm, respectively, effectively resolving the deformation and instability issues of the narrow coal pillars. [ABSTRACT FROM AUTHOR]

Short fiber reinforced polymers (SFRP) based on unidirectionally arrayed chopped strands (UACS) offer exceptional formability and great mechanical properties. To ensure its stability and safety in applications, it is crucial to enhance the impact performance of UACS laminates. This study investigated the low‐velocity impact (LVI) responses and damage evolution of UACS laminates with different slit sizes and continuous carbon fiber reinforced polymer (CFRP) laminates under various impact energies (4, 7, and 11 J). The curves of force and energy were recorded during LVI tests, and the post‐impact damage area was detected by the ultrasonic C‐scan technique. Moreover, a user‐defined subroutine VUMAT, containing a progressive damage model and a Johnson‐Cook constitutive model, was written to mimic the damage evolution. Based on experiments and numerical prediction, it was found that when the size was reduced from 25 to 5 mm, the vertical slits had the effect of suppressing delamination and could restrain the propagation of delamination, which explains the distinct difference in delamination area. Highlights: The effect of slit size on the impact behavior of UACS laminate was revealed.The damage mechanism was simulated with a progressive damage model.The novel UACS laminate exhibits excellent energy absorption capacity.The resistance of the slits greatly suppresses the delamination behavior. [ABSTRACT FROM AUTHOR]

AbstractThe reactive material-metal composite jet (RMM-CJ), exhibiting a dual penetration-enhancement effect is of growing concern. In the present study, the composite jets of reactive material-copper (RM–Cu), reactive material-titanium (RM–Ti), and reactive material-aluminum (RM–Al) impacting multi-spaced plates were studied experimentally and numerically. A comprehensive analysis of the damage effects was conducted based on experimental and simulation results. The results show that the damage area of each layer of plate is closely related to the mass distribution of reactive material. The relationship of the mass of each layer of reactive material with time is given, and the deflagration gain is quantified. The research results provide a useful reference for the design and optimization of reactive material-metal composite liners. [ABSTRACT FROM AUTHOR]

Unveiling the mechanical properties and damage mechanism of the complex composite structure, comprising backfill and surrounding rock, is crucial for ensuring the safe development of the downward-approach backfill mining method. This work conducts biaxial compression tests on backfill–rock under various loading conditions. The damage process is analyzed using DIC and acoustic emission (AE) techniques, while the distribution of AE events at different loading stages is explored. Additionally, the dominant failure forms of specimens are studied through multifractal analysis. The damage evolution law of backfill–rock combinations is elucidated. The results indicate that DIC and AE provide consistent descriptions of specimen damage, and the damage evolution of backfill–rock composite specimens varies notably under different loading conditions, offering valuable insights for engineering site safety protection. [ABSTRACT FROM AUTHOR]

The study of constitutive relationship and damage degradation is crucial in solving the stability challenges faced in the rock engineering. In this work, the stress-strain relationships of different type of rocks subjected to uniaxial loading processes are investigated in details. Experimental results demonstrate measurements, such as uniaxial compressive strength (UCS), tangent deformation modulus, peak strain, and Poisson's ratio (v). A novel piecewise constitutive model is proposed that utilizes both a constitutive model during compaction and a conventional damage model using the strain equivalence assumption and logistic growth theory to represent the characteristics of stress-deformation curves during both compaction and post-compaction stages. The performance of the proposed constitutive models in capturing deformation characteristics of damaged rocks is demonstrated to be more outstanding in comparison to existing models. In all experimental cases discussed in this study, the proposed model outperforms existing reference models in terms of the coefficients of determination ( R 2 ), with the former having coefficients of determination greater than 0.95. Furthermore, physical meanings of relevant model parameters are found to be closely associated with properties of experimental stress-strain curves. [ABSTRACT FROM AUTHOR]

To investigate the load-bearing capacity and failure modes of unidirectional fiber-reinforced laminates subjected to uniaxial loads, finite element analyses were conducted to predict mechanical responses such as plastic accumulation and damage evolution. The Ladeveze constitutive model based on the 2D continuum damage theory was introduced and a user material subroutine was developed based on this model to consider the plastic behavior of the composites, where the isotropic plastic strengthening was assumed. Subsequently, a LS-DYNA finite element simulation model for unidirectional laminate plates was established to explore typical failure behaviors under loading conditions of longitudinal tension, longitudinal compression, transverse tension, and in-plane shear, respectively. A comparative analysis with experimental results was carried out to validate the efficacy of the developed subroutine. Finally, a logarithmic rate-dependent correction function was introduced to predict the damage modes of composite materials under various strain rate loads. The sensitivity of the rate effect in unidirectional fiber-reinforced laminates and its correlation with load-bearing components were investigated. [ABSTRACT FROM AUTHOR]

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A compression module system placed under a microscope was utilized to conduct uniaxial compression testing of sandstone samples. The test system can acquire the image of crack propagation on the specimen surface in real time. The focus of this study was to analyze how the motion of sandstone composition particles affect the failure mechanism of the samples under minimal loading rates. The results indicate that the load displacement curves align with the macroscopic failure laws under different loading rates. Furthermore, the lower the loading rate, the greater the deformation and crushing degree of sandstone during failure. The failure mode becomes more complex and gradually transitions from tension failure to shear-tension failure. The crack evolution of sandstone was caused by the uncoordinated movement of its components, and the weak structure induces cracks under the action of external load. Microcracks are initially generated at the interface between mineral particles and the sandstone matrix and propagate along the boundary between mineral and matrix. The interaction between component particles in sandstone leads to the connection break between particles which forms microcracks, and results in local deformation of the sample. The aggregation of multiple cracks leads to the instability and failure of sandstone. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work explores the dynamic fracture characteristics of recycled tyre polymer (RTP) fibre reinforced concrete after exposure to 20, 105, 250, 400 and 600 °C. Split Hopkinson pressure bar tests were performed to characterize the dynamic compressive properties under strain rates of 40–120 s−1, in terms of the failure mode, strain-stress response, dynamic strength, dynamic increase factor (DIF), peak strain and energy absorption capacity. Results indicate that the failure pattern varies from splitting failure to core failure, and finally to pulverization failure due to strain rate effect, regardless of exposure temperatures. The dynamic strength and DIF are enhanced by strain rate effect but drop by 56.1% and 23.9% at 600 °C, respectively, while no explosive spalling occurs because of the thermal expansion of RTP fibres. The temperature-dependent dynamic fracture mechanism is closely related to the physicochemical reactions in the concrete matrix, bridging or rupture of RTP fibres and breaking of coarse aggregates. [ABSTRACT FROM AUTHOR]

This study used a static bidirectional multifunctional loading system. The system conducted bidirectional compression tests on scaled specimens of slurry masonry schist under freeze–thaw cycling conditions. This study aimed to investigate the influence of bidirectional stress coupling with freeze–thaw cycles on the mechanical properties of slurry masonry schist. The results indicate that lateral pressure can increase the peak stress of slurry masonry schist, while freeze–thaw cycles have an adverse effect on the material's internal pore structure, counteracting the gain effect of lateral pressure. This study also employed acoustic emission (AE) technology to analyze the evolution of slurry masonry schist failure characteristics. The findings reveal that freeze–thaw cycles accelerate the failure of slurry masonry schist during loading, and lateral pressure to some extent mitigates the damage development of slurry masonry schist. The synergistic effect of lateral pressure and freeze–thaw cycles alters the fracture mode of slurry masonry schist. Acoustic emission signal localization demonstrates numerous AE localization points in the interface transition zone, forming a coherent signal band where cracks propagate toward complete interface penetration. The crack extension process of the slurry masonry schist was investigated using the digital image correlation (DIC) method. The results indicated that macroscopic cracks formed in the strain localization zone, resulting in fracture damage to the specimens, with interfacial debonding identified as the primary failure mode for slurry masonry schist structures. [ABSTRACT FROM AUTHOR]

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