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This study systematically investigates the effects of high-power continuous wave laser (CWL) treatment on the mechanical behavior and failure mechanisms of SM400A steel, comparing these outcomes with those of untreated specimens. The findings reveal that while CWL treatment enhances surface hardness, it has minimal impact on the strength of thick structural steel components. However, excessive laser energy density leads to surface defects and softening of the microstructure, adversely affecting the material's toughness. This results in a reduction in elongation at fracture, transitioning the failure mode from ductile to brittle. The study concludes that to ensure the safe use of laser-treated structures, the laser energy density should be carefully controlled not to exceed 3000 J/cm2.

The tensile behavior of an injection mold glass fiber reinforced polyamide matrix composite was determined between 10-6-10-1 s-1 strain rates at 25, 65 and 90°C for the loading axis 0o, 30o and 90o to the fiber plane. Microscopic studies were conducted to identify typical fracture mechanism involved at different temperatures. The composite exhibited the highest flow stress and elastic moduli sensitivities on the strain rate in the 0o specimens, followed by the 30o and 90o specimens. The highest rate sensitivity was detected in the specimens tested at 25°C and the rate sensitivity declined as the test temperature increased from 25°C to 65 and 90°C. The observed rate sensitivity of the composite was ascribed to the rate sensitivity of the matrix while the elevated temperatures enhanced the fiber-matrix bonding.

Inspired by the microstructures of shells, SiC fibers (SiCf) are introduced into Ti layers, creating hybrid layers of SiCf/Ti, which are combined with Ti2AlNb foils to prepare multilayer SiCf/Ti–Ti2AlNb hybrids in a hot-pressed sintering instrument. The solid-phase bonding interface, mainly including the α+β biphasic structures and B2-rich phases, guarantees an ideal interface connection between the SiCf/Ti and Ti2AlNb layers after the sintering. Herein, the SiC fibers-made SiCf/Ti–Ti2AlNb presents a higher tensile strength and elasticity modulus on the tensile instrument of Model No. Byes (2010), compared with Ti/Ti2AlNb. During the tensile process, the brittle fractures of SiCffirst occur, and the loads are transferred to the bonding interface of the Ti2AlNb and Ti layers, generating the crack propagation and resulting in SiCf/Ti–Ti2AlNb fracture. This is mainly because the crack is extended in succession to the bonding interface that is composed of brittle phases such as O and α2, as well as ductile phases such as α, β and B2. This produces the ductile and brittle ruptures at the bonding interface, forming the ductile-brittle mixture fractures at the SiCf/Ti and Ti2AlNb interfaces. In the case of vertical fractures related to the fiber length, brittle fractures are observed on the SiC fibers, which produce high forces that affect their bonding interfaces, resulting in axial interstices and transverse fractures. These obtained results demonstrate a novel method for structural design and fabrication of the innovative composite materials.

This paper focuses on the high-temperature tensile failure mechanism of RTM (resin transfer moulding)-made symmetric and asymmetric composite T-joints. The failure modes as well as the load-displacement curves of symmetric (three specimens) and asymmetric (three specimens) composite T-joints were determined by tensile tests at room and high temperatures. Progressive damage models (PDMs) of symmetric and asymmetric composite T-joints at room and high temperatures were established based on mixed criteria, and the result predicted from the aforementioned PDMs were compared with experimental data. The predicted initial and final failure loads and failure modes are in good agreement with the experimental results. The failure mechanisms of composite T-joints at different temperatures were investigated by scanning electron microscopy. The results reveal that while the failure mode of asymmetric T-joints at high temperatures resembles that at room temperature, there is a difference in the failure modes of symmetric T-joints. The ultimate failure load of symmetric and asymmetric T-joints at elevated temperatures increases and reduces by 18.4% and 4.97%, albeit with a more discrete distribution. This work is expected to provide us with more knowledge about the usability of composite T-joints in elevated temperature environments.

Since Al-Mg-Si alloys are widely used in the transportation industry, it is important to produce a sound and robust weld between the sheets of these alloys. The focus of this work is on the tensile-shear and cross-tension strengths of the consumable pin-friction stir spot welds (CP-FSSWs) without an exit-hole between the Al-6061 aluminum sheets. Before welding, a hole was created at the joint region in the base sheets and then, it was filled using a rotating consumable pin. The tensile-shear, cross-tension, and microhardness tests were employed to evaluate the mechanical properties of the spot welds. The results showed that the pre-created hole was entirely filled during the welding process. While a complete bond was formed between the consumable pin and the lateral surface of the hole, there were three distinct regions at the interface of the pin and the bottom of the hole: complete bond, kissing bond, and defects. Enhancement of the tool rotational speed decreased the area of the complete bond in the weld compared to the other regions. A linear relationship existed between the bonding area and weld failure load in the cross-tension test. The proposed relationship approved the impact of the swirly region at the interface of the base sheets on the weld strength. While in the cross-tension test, the weld failure load decreased from ∼2800 to ∼1950 N, it improved from ∼10,500 to ∼12,000 N in the tensile-shear test with enhancement of the tool rotational speed from 700 to 2000 rpm. The hardness measurements demonstrated that there was no common heat affected zone softening after CP-FSSW.

Two types of the weld joint of Inconel 617 alloy were produced using gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) processes with ERNiCrCoMo-1 filler metal and ENiCrCoMo-1 electrode, respectively. The weld metal showed the segregation of the principle alloying elements like Mo and Cr along the inter-dendritic spaces, triggering the formation of secondary phases. The microstructure characterization of the interface ensured the high dilution, which could be attributed to the closeness in melting point and chemistry of base and filler metal. Microhardness variation, tensile testing at room and high temperature, and Charpy impact test were conducted to investigate the effect of the Mo segregation in the weld zone and heterogeneity in the microstructure of weldments on the mechanical behavior of both the welded joints. The cross-weld tensile tests were conducted at room temperature and 550°C. The tensile test samples failed from the weld zone for each condition with a tensile strength value close to the base metal, which ensured the applicability of the joint for end service. The tensile strength of GTAW-RT, GTAW-HT, SMAW-RT, and SMAW-HT were measured as 766 ± 22 MPa, 570 ± 5 MPa, 760 ± 7 MPa, and 600 ± 8 MPa, respectively. A non-uniform hardness plot was witnessed with the hardness of the GTAW-weld and SMAW-weld zone of 257 ± 8 HV and 285 ± 5 HV, respectively, in the transverse direction. The impact toughness of the weld zone was 84 ± 2 J and 48 ± 4 J for GTAW and SMAW weld zone. The average impact toughness of the GTAW-weld zone was approximately 42% higher than the value of the SMAW-weld zone. In a nutshell, it can be concluded that the welded joint of Inconel 617 produced using the GTAW process with ERNiCrCoMo-1 filler had the best metallurgical and mechanical properties.

Three-dimensional (3D) needled carbon fiber reinforced carbon and silicon carbide (C/C–SiC) composites have the significant advantages of low density, high strength, and long lifespan, which are widely used in aerospace and other industrial fields. In this paper, based on the microstructure of the composites, a multi-scale finite element model is established to predict their mechanical properties and failure behaviors under the tensile load. The multi-scale model has been validated by the static tensile test and the microstructure of fracture. With this model, the effects of the fiber volume fraction, the interfacial bonding strength, the content of residual silicon (Si) elements, and the porosity on the mechanical properties of needled C/C–SiC composites are systematically analyzed. The results show that the stress-strain curve of the composites under the longitudinal tensile load has two nearly linear segments. The final failure strength of the composites increases with the increase of the interfacial bonding strength, the fiber volume fraction and residual Si elements, while decreases with the increase of the porosity. In addition, based on the established multi-scale finite element model, the damage evolution process and failure mechanism of the needled composites are investigated in detail. The proposed scheme could effectively predict the mechanical properties of the needled C/C–SiC composites and capture the microscopic damage evolution, which would help to optimize the design of composites.

The addition of steel fibres to concrete can result in changes to its mechanical properties. Therefore, research has been conducted on the characterisation of unidirectional tensile performance failure of steel fibre nano high-strength concrete. Increasing the amount of steel fibre can significantly improve the concrete's crack resistance, tensile strength, and flexural stiffness. However, it also affects the deformation characteristics of concrete and reduces its stiffness. Research has shown that as the steel fibre content increases, the total deformation of concrete increases while the crack propagation width decreases. Excessive steel fibre content can lead to a decrease in the stiffness of concrete and adverse degradation. In practical applications, the appropriate amount of steel fibre should be selected based on the specific situation to ensure the mechanical properties and effectiveness of concrete.

Dynamic tensile fracturing of two quasi-brittle geomaterials during high strain rate spalling as observed in situ utilizing ultra-high speed single bunch X-ray phase-contrast radiography is presented (image acquisition rate of 1.4 MHz with 32 μm pixel size). A spalling experimental set-up, based on a single Hopkinson bar, has been developed to apply indirect dynamic tension with strain rates up-to 1000 s-1. Experiments were performed on a pink granite (low porosity content and large quantity of pre-existing cracks) and an ultra-high strength concrete (comparatively high porosity content and low quantity of pre-existing cracks). The in situ results show that the two tested materials exhibit notable differences in tensile failure patterns. In parallel, point-wise measurements of the rear face velocity have been obtained showing a pronounced difference in the velocity pull-back response. X-ray micro-tomography inspection has been performed on the samples post-mortem. The effects on the microstructure and the initial quantity of defaults on the observed dynamic tensile failure are discussed.

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Tensile failure in superplastic alumina shows a close similarity to ductile failure in metallic materials containing microvoids or hard inclusions. Microcracking, which appears as strain exceeding ~ 90% of the failure strain and leading to macroscopic cracking for final failure, is not caused by the propagation of the largest preexistent defects, but by extensive cavity coalescence. Such coalescence is found to occur as the thickness of the intervoid matrix decreases to a certain level due to an increase in the number and size of cavities. The data also show that there is no explicit critical grain size for the onset of microcracking, although microcracking and failure tend to occur at smaller strains as the initial grain size increases.

Sheet molding compounds (SMCs) as an alternative material for low-cost and lightweight automotive structural components require special attention to their failure behavior and collision safety. This study aims to analyze the energy-absorbing response and variability of unsaturated polyester matrix SMCs under the range of strain rates from 10−3/s to 500/s through quasi-static and dynamic tensile tests. Additionally, the tensile process and fracture morphology were characterized using Digital Image Correlation and Scanning Electron Microscopy to reveal the underlying rate-dependent failure mechanism. The results demonstrate a pronounced positive correlation between the tensile strength and absorbed energy of SMCs with strain rates. Specially, the absorbed energy exhibits substantial variability, primarily attributable to the plastic damage behavior during the nonlinear phase. A transition in the failure mode from debonding to pseudo-delamination, accompanied by a more extensive failure area at high strain rates, serves as the main mechanism for enhancing the material energy absorption capacity.

In this paper, shale gas cores from the Lower Silurian Longmaxi Formation in the Zhaotong National Shale Gas Demonstration Area were selected to study the hydration effect of different fluids on the fracture morphology inside the shale, the rock tensile strength and the Brazilian tensile failure mode. Fresh water and slick water were adopted for hydration pretreatments and the CT technique was used to compare the changes of the fabric in the shale. Then, Brazilian tensile tests were carried out to study the tensile strength and tensile failure modes of the shale specimen after hydration pretreatment. Finally, two horizontal wells in the study area were selected to perform pilot tests of hydration pretreatment in their fracturing operation sites. And the following research results were obtained. First, in the process of spontaneous imbibition, the hydration effect of fresh water is superior to that of slick water in promoting the fracture complexity of marine shale in the same hydration duration. Second, fresh water has greater surface tension and lower viscosity and its hydration effect can not only promote the propagation of original fractures but induce new micro-fractures or branches, while the hydration effect of slick water mainly promotes the propagation of original fractures. Third, due to hydration effect, marine shale is damaged and its tensile strength is reduced. After the hydration pretreatment by fresh water and slick water, the tensile strength of the shale specimens are reduced by 35.6% and 18.1%, respectively. Fourth, according to the propagation paths of main fractures, the Brazilian tensile failure modes of hydrated shale can be divided into four types (i.e., step shaped, dog-leg shaped, branching shaped and arc shaped) or their combinations, while the tensile failure mode of unhydrated shale is only a straight line. Fifth, hydration effect can effectively increase the complexity of the hydraulic fractures in marine shale, so if the conditions permit, it is recommended to inject a certain amount of fresh water at a high pumping rate within the limited pressure after perforation and to shut in the well until the hydraulic fracturing operation. And in order to reduce the difficulties of pumping the proppant during the hydraulic fracturing operation, a pumping strategy of “low proppant concentration, large volume of slurries” can be adopted to reach the expected proppant volume.

Fracture toughness and surface energy density are critical parameters in the simulation of hydraulic fracturing in shale formations. In this study, a microscopic insight into the mechanisms of tensile failure in kerogen is advanced by molecular dynamics simulations for the first time. The elastic properties, critical stress, surface energy density, and fracture toughness of kerogen are analyzed systematically. Our work reveals that kerogen is potentially a weak component in shale, which may serve as a region of fracture initiation and preferential fracture propagation path. The critical energy release rate Gcis higher than the doubled surface energy density γs(Gc≥ 2γs), which indicates that there may be pronounced plastic deformation in kerogen in the tensile failure. This work sets the stage for the determination of various shale mechanical properties and surface energy density to examine fracturing effectiveness in shale media from the molecular scale.

Softening of the heat-affected zone degrades the mechanical properties of high-strength steel-welded joints. This work revealed the key mechanism to suppress the adverse effects of the soft zone on joint performance by analyzing the constraint between different zones. The base metal (BM) can compete with the soft zone for plastic deformation when the soft zone is strongly constrained by the hard zone, which helps to disperse local strain and prevent premature necking. The constraint mode of the soft zone tends to evolve asymmetrically from bilateral to unilateral during the deformation. Reducing the width of the soft zone helps to achieve unilateral constraint, thus shifting the fracture location from the soft zone to the BM.

Sand production is a challenging issue in upstream oil and gas industry, causing operational and safety problems. Therefore, before drilling the wells, it is essential to predict and evaluate sanding onset of the wells. In this paper, new poroelastoplastic stress solutions around the perforation tunnel and tip based on the Mohr–Coulomb criterion are presented firstly. Based on the stress models, a tensile failure induced sanding onset prediction model for cased-perforated gas wells is derived. Then the analytical model is applied to field data to verify its applicability. The results from the perforation tip tensile failure induced sanding model are very close to field data. Therefore, this model is recommended for forecasting the critical conditions of sand production analysis. Such predictions are necessary for providing technical support for sand control decision-making and predicting the production condition at which sanding onset occurs.

Sills, saucer‐shaped sills, and cone sheets are fundamental magma conduits in many sedimentary basins worldwide. Models of their emplacement usually approximate the host rock properties as purely elastic and consider the plastic deformation to be negligible. However, many field observations suggest that inelastic damage and shear fracturing play a significant role during sill emplacement. Here we use a rigid plasticity approach, through limit analysis modeling, to study the conditions required for inelastic deformation of sill overburdens. Our models produce distinct shear failure structures that resemble intrusive bodies, such as cone sheets and saucer‐shaped sills. This suggests that shear damage greatly controls the transition from flat sill to inclined sheets. We derive an empirical scaling law of the critical overpressure required for shear failure of the sill's overburden. This scaling law allows to predict the critical sill diameter at which shear failure of the overburden occurs, which matches the diameters of natural saucer‐shaped intrusions' inner sills. A quantitative comparison between our shear failure model and the established sill's tensile propagation mechanism suggests that sills initially propagate as tensile fractures, until reaching a critical diameter at which shear failure of the overburden controls the subsequent emplacement of the magma. This comparison also allows us to predict, for the first time, the conditions of emplacement of both conical intrusions, saucer‐shaped intrusions, and large concordant sills. Beyond the application to sills, our study suggests that shear failure significantly controls the emplacement of igneous sheet intrusions in the Earth's brittle crust. We investigate the conditions for inelastic deformation induced by inflating sills for which we propose an empirical scaling lawThe damage patterns calculated in our simulations resemble the inclined sheets of cone sheets and saucer‐shaped sillsSills propagate laterally by tensile opening at sill tips, but at a given size shear failure may become favored

The aim of the present study is to utilize fractographic methods employing scanning electron microscope (SEM) images to investigate the effects of build direction and orientation on the mechanical response and failure mechanism for Acrylonitrile–Butadiene–Styrene (ABS) specimens fabricated by fused deposited modeling (FDM). The material characterized here is ABS-M30 manufactured by Stratasys, Inc. Measurements of tensile strength, elongation-at-break and tensile modulus measurements along with the failure surfaces were characterized on a range of specimens at different build direction and raster orientation: ±45°, 0°, 0/90°, and 90°. The analysis of mechanical testing of the tensile specimens until failure will contribute to advances in creating stronger and more robust structure for various applications. Parameters, such as build direction and raster orientation, can be interdependent and exhibit varying effects on the properties of the ABS specimens. The ABS-M30 specimens were found to exhibit anisotropy in the mechanical response when exposed to axial tensile loading. The stress-strain data was characterized by a monotonic increase with an abrupt failure signifying brittle fracture. In certain combinations of build direction and raster orientation tensile failure was preceded by slight softening. The tensile strength and modulus, and elongation-at-break were found to be highly dependent upon the raster orientation and build direction. The relationship between the mechanical properties and failure was established by fractographic analysis. The fractographic analysis offers insight and provides valuable experimental data for the purpose of building structures in orientations tailored to their exemplified strength. For instance, specimens loaded such that bonds between adjacent rasters are the primary load bearing mechanism offer the least significant failure resistance. Other examples are shown where artifacts of the FDM fabrication process act to enhance tensile strength when configured properly with respect to the load. The results highlighted in this study are fundamental to the development of optimal design of complex ultra-light structure weight with increased structural efficiency. The study also presents a systematic scheme employing analogs to traditional fiber-reinforced polymer composites for the designation of build orientation and raster orientation parameters.

This paper investigates the influence of concrete/gypsum bedding layers and their orientation angles on the tensile failure mechanism in the three-point bending test based on experiments and numerical simulations. Rectangular samples containing different combinations of concrete and gypsum layers were prepared, i.e. one layer of gypsum and one layer of concrete, one layer of gypsum and two layers of concrete, and two layers of gypsum and two layers of concrete. In each configuration, bedding layer angles varied between 0° and 90° with increment of 30°. A total of 36 specimens including 12 configurations were prepared and tested. In addition, numerical simulations were conducted on the concrete/gypsum bedding layers at different angles of 0°, 15°, 30°, 45°, 60°, 75°, and 90°. Results show that the bedding layer orientation and bedding layer thickness affect the observed tensile failure process including the failure pattern and tensile strength. A pure tensile failure occurred when the bedding layer angle was 0°, while a sliding failure evolved by increasing the joint angle. When the bedding layer angle was 90°, the failure in boundary of layer was observed. Specimens with one layer of concrete and one layer of gypsum at 0° inclination angle had the highest tensile strength. However, increasing the number of layers and inclination angles decreased the tensile strength of specimens as the number of weak layers in the direction of loading increased.

Welding armour steel plate is a crucial task in the construction of combat vehicle structures. The shield metal arc welding (SMAW) with austenitic stainless steel (ASS) filler is used to prepare the defect free weld joints under suitable welding parameters. Tensile property enhancement in the fusion zone of the weld joint inhibits bullet penetration in a combat environment. An examination has also been conducted into the effect of microstructures in base metal, weldments, and the influence on tensile fractured surfaces. Tensile failure occurs in the weld centreline due to the reduced tensile strength of the filler material. When compared to the relevant literature, these welds demonstrated 48% joint efficiency and good tensile strength. This present work was development of a finite element analysis (FEA) model to analyse the tensile failure of base metal and weld joints with different factors of safety (FOS) such as FOS 0, FOS 1.5, and FOS 3. The FEA was carried out to predict the load-carrying capacity under tensile load. The simulation and experimental findings concur, implying that the suggested approaches were utilized effectively for structural analysis of armour weld joint using typical FEA techniques.

Natural and synthetic inclusions may modify the tensile strength and the failure pattern of surrounding rocks. Understanding the failure mechanism could improve rock failure prediction and induced geohazard mitigation. Due to difficulties in controlling the geometrical and mechanical properties of embedded inclusions in the laboratory, we simulate the dynamic tensile failure of inclusion-bearing rock specimens using a two-dimensional particle flow code model. We investigate the effects of strength ratio, loading rate, and treatment temperature on the nominal tensile strength of inclusion-bearing specimens and discuss the brittleness index to interpret the strength evolution. We identify the dominant effect on the nominal tensile strength as strength ratio for a low tensile strength inclusion and loading rate and treatment temperature for a high tensile strength inclusion. The change in dominant effect is associated with induced cracks primarily formed in the rock/inclusion part with lower tensile strength and highlights key factors to control inclusion-induced rock failure. This study also reveals that low strength, large size inclusions promote a decrease in brittleness index and accelerate the degradation of inclusion-bearing rocks.

Static and dynamic splitting tests were conducted on ring marble specimens with different internal diameters to study the tensile strength and failure modes with the change of the ratio of internal radius to external radius (ρ) under different loading rates. The results show that the dynamic tensile strength of disc rock specimen is approximately five times its static tensile strength. The failure modes of ring specimens are related to the dimension of the internal hole and loading rate. Under static loading tests, when the ratio of internal radius to external radius of the rock ring is small enough (ρ<0.3), specimens mostly split along the diametral loading line. With the increase of the ratio, the secondary cracks are formed in the direction perpendicular to the loading line. Under dynamic loading tests, specimens usually break up into four pieces. When the ratio ρreaches 0.5, the secondary cracks are formed near the input bar. The tensile strength calculated by Hobbs' formula is greater than the Brazilian splitting strength. The peak load and the radius ratio show a negative exponential relationship under static test. Using ring specimen to determine tensile strength of rock material is more like a test indicator rather than the material properties.

Mechanisms of blast-induced Traumatic Brain Injury (BTBI), particularly those linked to the primary pressure wave, are still not fully understood. One possible BTBI mechanism is cavitation in the cerebrospinal fluid (CSF) caused by CSF tensile failure, which is likely to increase strain and strain rate in the brain tissue near the CSF. Blast loading of the head can generate rarefaction (expansion) waves and rapid head motion, which both can produce tensile forces in the CSF. However, it is not clear which of these mechanisms is more likely to cause CSF tensile failure. In this study, we used a high-fidelity 3-dimensional computational model of the human head to test whether the CSF tensile failure increases brain deformation near the brain/CSF boundary and to determine the key failure mechanisms. We exposed the head model to a frontal blast wave and predicted strain and strain rate distribution in the cortex. We found that CSF tensile failure significantly increased strain and strain rate in the cortex. We then studied whether the rapid head motion or the rarefaction wave causes strain and strain rate concentration in cortex. We isolated these two effects by conducting simulations with pure head motion loading (i.e. prescribing the skull velocity but eliminating the pressure wave) and pure blast wave loading (i.e. eliminating head motion by fixing the skull base). Our results showed that the strain increase in the cortex was mainly caused by head motion. In contrast, strain rate increase was caused by both rapid head motion and rarefaction waves, but head motion had a stronger effect on elevating strain rate. Our results show that rapid motion of the head produced by blast wave is the key mechanism for CSF tensile failure and subsequent concentration of strain and strain rate in cortex. This finding suggests that mitigation of rapid head motion caused by blast loading needs to be addressed in the design of protective equipment in order to prevent the tensile failure of CSF.

The nonlinear finite deformations and ultimate failure modes of photo-cured polymers are closely related to the ambient temperatures, typically exhibiting enhanced stretchability and a peak of ultimate break strain near the glass transition temperature Tg. The origin of this type of temperature-dependent failure phenomenon lies in the evolution of visco-elasto-plastic flowing dynamics as well as the alteration of polymer chain mobility during glass transition. In the past few decades, theoretical models for the strength of polymers were developed independent of the visco-elasto-plastic deformation history and the glass transition dynamics. These models could not provide reasonable explanations for the peak of ultimate break strain in photo-cured polymers, nor predict the poor stretchability at ultra-low and ultra-high temperatures. In this paper, we propose a general model for the temperature-dependent deformation and tensile failure of photo-cured polymers, in which the breaking phenomenon is dominated by a competition between the brittle failure at low temperature, the visco-plastic failure at moderate temperature and the hyperelastic failure at high temperature. Through the comparison between theoretical predictions and typical experiments, the model is proved to be efficient in predicting the deformation and failure of both photo-cured thermosets and thermoplastics.

Off-axis plies have a great influence on the tensile failure stress of carbon fiber reinforced polymer (CFRP) multidirectional laminate. Matrix cracks in the off-axis plies will cause negative effect on the layers, leading to fatal failure of the laminate. A microscale cohesive zone model is proposed to explore the influence of matrix cracks in the off-axis plies on the tensile failure of [0/th]ns laminates. Simulations of tensile failure of [0/th]s laminate were performed by varying the off-axis ply angle th ranging from 15deg to 90deg and the cohesive properties to investigate the effects of off-axis plies to the failure of the laminates. Tensile tests of [0/th]2s laminates with various off-axis ply angles were conducted to validate the simulations of microscale model. The simulation results with matrix cracking are in high agreement with the experimental results, illustrating the influence of off-axis plies on the tensile failure of [0/th]ns laminates.

Fibre-hybrid composites are attracting an ever-increasing interest from academia and industry. It is therefore vital to develop a solid understanding of their basic mechanical properties. Measuring and predicting the tensile failure of hybrid composites however remains a challenging task. This paper describes how failure develops in unidirectional (UD) hybrid composites, and how this can be predicted using fibre break models. It also provides recommendations for experimental measurements of the hybrid effect, which is a synergetic increase of the failure strain of low elongation fibres when hybridised with higher elongation fibres. Finally, limitations of our understanding of the tensile failure of hybrid composites are discussed and recommendations for future research are proposed.

Characteristics of root pullout resistance determine the capacity to withstand uprooting and the slope protection ability of plants. However, mechanism underlying the uprooting of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau, China remains unclear. In this study, a common taproot-type shrub, Caragana korshinskiiKom., in northeastern Qinghai-Xizang Plateau was selected as the research material. Mechanism of root-soil interaction of vertical root of C. korshinskiiwas investigated via a combination of a single-root pullout test and numerical simulation analysis. The results indicated that, when pulling vertically, axial force of the roots decreased with an increase in buried depth, whereas shear stress at root-soil interface initially increased and then decreased as burial depths increased. At the same buried depth, both axial force and shear stress of the roots increased with the increase in pullout force. Shear stress and plastic zone of the soil surrounding the root were symmetrically distributed along the root system. Plastic zone was located close to the surface and was caused primarily by tensile failure. In nonvertical pulling, symmetry of shear stress and plastic zone of the soil surrounding the root was disrupted. We observed larger shear stress and plastic zones on the side facing the direction of root deflection. Plastic zone included both shear and tensile failure. Axial force of the root system near the surface decreased as deflection angle of the pullout force increased. When different rainfall infiltration depths had the same vertical pulling force, root axial force decreased with the increase of rainfall infiltration depth and total root displacement increased. During rainfall infiltration, shear stress and plastic zone of the soil surrounding the root were prone to propagating deeper into the soil. These findings provide a foundation for further investigation of soil reinforcement and slope protection mechanisms of taproot-type shrub species in the loess area of northeastern Qinghai-Xizang Plateau and similar areas.

Applying steel slag (SS) to mine backfilling not only alleviates environmental pressure caused by solid waste disposal but also provides a cost-effective and high-performance filling material for mining operations. Although SS-based backfill (SS-CPB) has been widely used in shallow surface mining, its mechanical properties under deep mining conditions still require further investigation. This study examines the mechanical properties and damage evolution patterns of SS-CPB under the combined effects of high-temperature curing and cyclic loading. The results indicate that as the curing temperature increases, the peak strength, elastic modulus, and stress yield level of SS-CPB exhibit an initial increase followed by a decrease. At a curing temperature of 60 °C, SS-CPB achieves its maximum peak strength (5.11 MPa), elastic modulus (0.61 GPa), and stress ratio (σc/σp) of 94.6%. High-temperature curing enhances the hydration reaction of SS-CPB and accelerates the crystallization of C–S–H gel, leading to increased material brittleness, The brittleness indices of SS-CPB under curing conditions of 20 °C, 40 °C, 60 °C, and 80 °C are 40.2%, 56.6%, 76.5%, and 95.5%, respectively. Consequently, the failure mode transitions from tensile failure to a combined “tensile + shear” failure mode. With increasing mining depth and geothermal temperature, the plasticity and ductility of the backfill material are enhanced after cyclic static loading. The coupled effect of fatigue loading and high-temperature conditions intensifies the propagation of initial pores and microcracks in the interfacial transition zone (ITZ), resulting in a more developed “tensile + shear” crack network in the specimens.

It is important to analyze the damage evolution process of surrounding rock under different water content for the stability of engineering rock mass. Based on digital speckle correlation (DSCM), acoustic emission (AE) and electromagnetic radiation (EMR), uniaxial hierarchical cyclic loading and unloading tests were carried out on sandstones with different fracture numbers under dry, natural and saturated water content, to explore the fracture propagation, failure precursor characteristics and damage response mechanism under the influence of water content effect. The results show that with the increase of water content, the peak stress and crack initiation stress decrease gradually, and the decreases are 15.28%–21.11% and 17.64%–23.04%, respectively. The peak strain and crack initiation strain increase gradually, and the increases are 19.85%–44.53% and 19.15%–41.94%, respectively. The precracked rock with different water content is mainly characterized by tensile failure at different loading stages. However, with the increase of water content, the proportion of shear cracks gradually increases, while acoustic emission events gradually decrease, the dissipative energy and energy storage limits of the rock under peak load gradually decrease, and the charge signal increases significantly, which is because the lubrication effect of water reduces the friction coefficient between crack surfaces.

The thermal effects of coal combustion considerably influence the physical and chemical properties, structural characteristics, and stability of rocks, posing a serious threat to the safety of coal mining operations. In this study, the impacts of temperature on the physical and chemical characteristics (i.e., mineral phase, microstructure, and mechanical strength) of sandstone were investigated by employing experimental methods, including microstructural analysis, uniaxial acoustic emission (AE), and nuclear magnetic resonance (NMR). The results indicate that temperature alters the mineral phase and the pore characteristics, and these two factors jointly affect the mechanical properties of sandstone. The influence of temperature on the mechanical strength of sandstone is categorized into low-temperature strengthening and high-temperature damage, with a threshold temperature identified at 600 °C. The low-temperature strengthening effect encompasses both pore strengthening and mineral phase strengthening, while the high-temperature damage effect primarily results from pore damage. As the experimental temperature rises, both the number of AE events and the AE energy transition from a surge in the post-peak failure stage to a stepwise increase during the loading process. This transition implies that the failure mode of the sandstone sample evolves from brittle failure to tensile failure.

Under the joint action of anchoring force and high in situ stress, the broken rock mass (BRM) in deep metal mines is actually under three-dimensional (3D) compressive stress, and its triaxial compression mechanical behavior is the key factor to control the stability of the surrounding rock. Therefore, it is necessary to perform research on the macro-mechanical behavior and micro-structural evolution of BRM under such similar stress state. In this work, based on 2D images, we propose a high-efficiency and low-cost method to reconstruct the 3D topographic features of the BRM. The particle flow code is used to study the effects of confining pressures and particle sizes on the mechanical properties, porosity, coordination number, acoustic emission characteristics, and fragmentation characteristics of the BRM. The results show that as the confining pressure increases, the compressive capacity and volume shrinkage of the BRM increase. The compressive capacity of the BRM reduces, and the secondary fragmentation become more violent with the increasing of particle sizes. At lower confining pressure, the rotation and translation of the BRM are main reasons for the change in the porosity. At higher confining pressure, the secondary fragmentation of the BRM as well as the migration of the small volume of rock are responsible to the change in the porosity. Secondary fragmentation of the BRM is mainly induced by tensile failure. The ratio between shear and tensile cracks in number decreases with increasing particle size of BRM. The results can provide some guides for the support design of the BRM in deep metal mines.

Many advanced rock breaking methods are emerged form improving the ROP in deep formation drilling in recent years, such as electric pulse rock breaking, ultrasonic rock breaking and hydraulic rock breaking. However, the traditional mechanical rock breaking is still the mainstream rock-breaking method. A detailed understanding of the rock cutting mechanism is essential to achieve high efficiency in rock breaking and to optimize the cutting parameters. This study establishes the simulation model of heterogeneous granite cut by polycrystalline diamond compact (PDC) cutter using FDEM, and the friction work factor is put forward to characterize the friction work proportion of PDC cutter in cutting process. Analysis is done on the variations in friction work factor, force, and failure mechanism of granite under different cutting depths. The results show that the three-dimensional force increase gradually with the increase of cutting depth. When the cutting depth is shallow, the tensile (Type I) failure is dominated, ductile failure mainly occurs to granite and the size of chips is small. When the cutting depth is deep, the proportion of tensile failure is low, the internal shear crack of granite gradually dominates, the failure mode of granite gradually changes to brittle failure, the chips gradually become larger. Friction work factor and failure factor can visualize the change of friction energy consumption of PDC cutter in rock cutting and the failure mode of rock. This study leads to an enhanced understanding of rock breaking mechanisms in rock cutting, and provides the basis to improve the PDC bit design.

Considering the fact that most coal mines in China involve extracting multiple seams, the cumulative overburden rock damage caused by the sequential mining of multiple seams is a scientific problem that must be addressed. In this study, the overburden failure and fracture propagation behavior of two typical, spatially overlapping, sequentially extracted seams #2−2and 4−2of the Buertai coal mine in the Shendong coalfield were systematically investigated. The results showed that the fractal dimension of overlying strata fractures exhibited a “power function” increasing trend with the advancing distance. The height of the overburdened hydraulic fracture zone (HFZ) of seam #2−2increased by 26.2% due to the additional disturbance caused by the extraction of seam #4−2. The total height of the connected HFZs of two seams was approximately 155 m. The upper seam extraction had a significant depressurization effect on the lower seam in that the vertical stress generally decreased. The front abutment pressure increased with the advance distance before the goaf was square, then decreased, and finally increased abruptly at a location approximately 100 m from the stopping line. The total overburden failure volume during the sequential extraction increased quasi-exponentially, at first with the advance distance and then linearly after the overlying strata completely failed. As the advance distance increased, the ratio of tensile failure increased and exceeded that of shear failure. The ratio of tensile to shear failures stabilized at 1.5:1 after the complete failure of the overlying strata. The results also provide a basis for understanding the overburden failure behavior and analyzing the HFZ of sequentially extracted multiple seams and a reference for water-preserving coal mining and mine hazard control and prevention.

Coal wall spalling characteristics and stability control mechanisms in steeply inclined coal seam (SICS) mining are more complex and dynamic due to the imbalanced mechanical constraint environment of the coal wall. This study investigates the characteristics of coal wall spalling in SICS mining using field measurements, theoretical analysis, and numerical simulations. The internal relationship between coal wall spalling and different influencing factors is also established, and the corresponding coal wall stability control measures are put forward. Results indicate that the primary form of coal wall spalling is wedge-shaped. Under the combined action of roof pressure and gravity, the wedge body produces two components along the dip and strike directions, forming two structural planes, a and b. The a-plane predominantly experiences shear slip failure, while the b-plane primarily undergoes tensile failure. The failure criteria for the a-plane and b-plane of the wedge body are determined, with mining height, coal strength, roof pressure, and coal seam dip angle being the main influencing factors in SICS mining. The stability relationship of the coal wall under various advancing distances is investigated using the 3DEC numerical simulation. The majority of coal wall spalling occurs as an asymmetric wedge body, and the relationship between different influencing factors and coal wall spalling is examined. A comprehensive preventive and control technique for coal wall spalling in SICS mining is proposed. The engineering application demonstrates positive results and provides theoretical and technical guidance for the prevention and control of coal wall spalling in SICS mining.

To study the failure modes and influence of related factors on the failure modes of pillars with weak interlayers, a hard − soft − hard structural mechanical model of pillars was established, in which a pillar with a weak interlayer in a limestone mine was used as the research object, and the expressions of the stress components of the weak interlayer were derived. On the basis of the mechanical characteristics of the weak interlayer, the failure modes of pillars with weak interlayers can be divided into tensile failure, shear failure, and comprehensive failure. Combined with the safety factor, the failure characteristics of the weak interlayer at different dip angles (θ) and thicknesses (h) were analyzed. The results revealed that the failure modes of pillars with weak interlayers are doubly influenced by the dip angle and the thickness of the weak interlayer. The compression safety factor (Fp) is positively correlated with θand negatively correlated with h. The smaller his, the greater the slope change of the Fpcurve. The shear safety factor (Ft) is negatively correlated with the dip angle in the range of 0° < θ≤ 45° but positively correlated with the dip angle in the range of θ> 45°. When θis fixed, the change in hhas little effect on Ft, and the maximum shear stress is at the top of the upper interface and the bottom of the lower interface. The numerical simulation results and engineering examples verify the rationality of the theoretical calculation results. The research results provide theoretical support for the safe mining of such mines.

Tensile strength is one of the important mechanical parameters for controlling the development of cracks in the Loess Plateau. However, the tensile strength of soil is difficult to be precisely measured due to the lack of satisfying laboratory techniques. Unconfined penetration test (UPT) is commonly used as an indicator to predict soil tensile strength characteristics, while there has been less research study about test parameter values range of UPT and micromechanical characteristics at failure. This study finished 50 groups of UPTs of remolded loess with different disk diameters (12.36–27.81 mm) at various sample heights (37–87 mm) based on Q2loess in Lintong areas, and the crack development and failure essence in the different failure modes process were investigated by the discrete element modeling. The results showed that disk diameters and sample height were closely correlated with the failure mode. The failure of remolded loess in the UPT is not only tensile failure, which also can occur compression failure and tensile–compression coupling failure. Among them, when the ratio of disk diameters to sample height is about in the range of 0.189–0.309, the sample appears tensile failure. In addition, the ratio of compressive and tensile crack numbers in the sample is 0.16–0.22 in the tensile failure mode. The numerical simulation method provides a way for the observation of failure process and crack development, thereby improving the understanding of failure essence in UPT. The findings will provide a reference way to improve test theory and method of loess tensile strength.

Abstract: A simple method for preparing artificial kidney stones with varying physical properties is described. BegoStone was prepared with a powder-to-water ratio ranging from 15:3 to 15:6. The acoustic properties of the phantoms were characterized using an ultrasound transmission technique, from which the corresponding mechanical properties were calculated based on elastic wave theory. The measured parameters for BegoStone phantoms of different water contents are: longitudinal wave speed (3,148–4,159 m/s), transverse wave speed (1,813–2,319 m/s), density (1,563–1,995 kg/m3), longitudinal acoustic impedance (4.92–8.30 kg/m2 s), transverse acoustic impedance (2.83–4.63 kg/m2 s), Young’s modulus (12.9–27.4 GPa), bulk modulus (8.6–20.2 GPa), and shear modulus (5.1–10.7 GPa), which cover the range of corresponding properties reported in natural kidney stones. In addition, diametral compression tests were carried out to determine tensile failure strength of the stone phantoms. BegoStone phantoms with varying water content at preparation have tensile failure strength from 6.9 to 16.3 MPa when tested dry and 3.2 to 7.1 MPa when tested in water-soaked condition. Overall, it is demonstrated that this new BegoStone preparation method can be used to fabricate artificial stones with physical properties matched with those of natural kidney stones of various chemical compositions.

Armour grade steel is high strength steel and it is used to build structures in defence applications. The weld zone of the armour weldment has lower tensile strength and deformation fracture in combat vehicles. In this study, experimental, computational, and analytical approaches are used to measure the failure assessment of tensile weld specimens. Tensile weld specimens are tested at strain rates of 0.1, 0.5, and 1 m/s and joint efficiencies of 56.2%, 61.2%, and 66.3%. Microstructures can be used to find a weld zone with different zones and ductile cracks in the fusion zone of tensile specimens. The computational approach of the Johnson Cook material model and the damaged material model is examined to assess the failure in the tensile test specimens with the help of different strain rates and temperatures. The analytical approach is used to calculate the stress, strain, and displacement values using safety applicable factors concerning tensile failure for armour grade steel, filler metal, and weld metal. According to MIL-STD-1185 standard, the different strain rates of tensile strength have been accepted within the range. The computational and analytical results are excellent methods for predicting tensile failure in armour weldments.

Isolation bearings play an important role in the seismic resilience of highway bridges. Flexible and high‐strength reinforcement has been applied in elastomeric isolation bearings to substitute conventional rigid steel plate reinforcement to enhance their lateral performance, for example, lower lateral stiffness and larger deformability. However, the main literature shows that existing flexible reinforcement, such as carbon/glass fiber fabric, may not guarantee a sufficient vertical load‐carrying capacity of elastomeric bearings to meet the design requirement of 30 MPa considering the vertical seismic effect. To this end, the emerging high‐strength steel woven wire mesh was introduced as an alternative flexible reinforcement for the bearings in this study to increase their ultimate compression capacity while maintaining superior lateral performance. Vertical compression tests were conducted on 34 specimens of the proposed unbonded steel‐mesh‐reinforced bearings (USRBs) to investigate the ultimate compression capacity. In addition to the general ultimate behavior of USRBs under vertical loading, the influence of various design parameters (i.e., individual rubber layer thickness, number of reinforcement layers, bearing design load) was investigated through comparisons among the specimens. From the test results, the compressive failure mechanism of USRBs was unveiled, which originated from the tensile failure of the steel mesh reinforcement. The steel mesh reinforcement was proved to increase the bearing ultimate compression capacity to an average of 52.0 MPa compared to fiber‐reinforced bearings, with 85% of specimens exceeding 30 MPa. Moreover, the compression capacity of USRBs was identified to be significantly affected by the individual rubber layer thickness. Specific discussions were further provided concerning the influence of potential manufacturing defects. Finally, suggestions were provided to further enhance the ultimate compression capacity of USRBs based on the results and discussions. The newly issued Chinese seismic design code for highway bridges has increased the vertical design load requirement for isolation bearings to 30 MPa. To meet this standard, we introduced high‐strength steel wire woven mesh as reinforcement for fiber‐reinforced bearings. The ultimate compression capacity of steel‐mesh‐reinforced rubber bearings was experimentally investigated, along with the factors influencing their performance. The results show that steel‐mesh reinforcement ensures that 85% of the specimens achieve a compression capacity exceeding 30 MPa. This capacity can be further improved by reducing the individual rubber layer thickness, decreasing the number of reinforcement layers, and minimizing reinforcement distortion or dislocation.

With the increase of underground engineering construction depth, the phenomenon of surrounding rock sudden failure caused by supporting structure failure occurs frequently. The conventional unloading confining pressure (CUCP) test cannot simulate the plastic yielding and instantaneous unloading process of supporting structure to rock. Thus, a high stress loading-instantaneous unloading confining pressure (HSL-IUCP) test method was proposed and applied by considering bolt’s fracture under stress. The wall thickness of confining pressure plates and the material of bolts were changed to realize different confining pressure loading stiffness (CPLS) and lateral maximum allowable deformation (LMAD). The superiority of HSL-ICPU method is verified compared with CUCP. The rock failure mechanism caused by sudden failure of supporting structure is obtained. The results show that when CPLS increases from 1.35 to 2.33 GN/m, rock’s peak strength and elastic modulus increase by 25.18% and 23.70%, respectively. The fracture characteristics change from tensile failure to tensile-shear mixed failure. When LMAD decreases from 0.40 to 0.16 mm, rock’s residual strength, peak strain, and residual strain decrease by 91.80%, 16.94%, and 21.92%, respectively, and post-peak drop modulus increases by 140.47%. The test results obtained by this method are closer to rock’s real mechanical response characteristics compared with CUCP.

Rockburst has always been a challenge for the safe construction of deep underground engineering. This study investigated the rockburst characteristics in highly-stressed D-shape tunnels under impact loads from rock blasting and other mining-related dynamics disturbances. The biaxial Hopkinson pressure bar was utilized to apply varying biaxial prestress and the same impact loads to cube specimens with D-shape hole. High-speed camera and digital image correlation (DIC) were used to capture the failure process and strain field of specimen. The test results demonstrate that the D-shape hole specimen experience rockburst under coupled static stress and impact load. Under this circumstance, the rockburst mechanism of the D-shaped hole specimens involves spalling in sidewall induced by impact load, indicating dynamic tensile failure. The high static prestress provides the initial stress field, while the impact load disrupts the stress equilibrium, result in the stress or strain concentration in the sidewall of the D-shape hole, inducing rockburst. Moreover, the rockburst process can be divided into (1) calm stage, (2) crack initiation, propagation, and coalesce stage, (3) spalling stage and (4) rock fragments ejection stage. Impact load triggers rockburst occurrence, while vertical stress further determines the rockburst characteristics. The influence range and magnitude of strain concentration zone and displacement deformation of the tunnel surrounding rock increases with increasing vertical stress, thus inducing more severe rockburst.

The redistribution of three-dimensional (3D) geostress during underground tunnel excavation can easily induce to shear failure along rockmass structural plane, potentially resulting in engineering disasters. However, the current understanding of rockmass shear behavior is mainly based on shear tests under 2D stress without lateral stress, the shear fracture under 3D stress is unclear, and the relevant 3D shear fracture theory research is deficient. Therefore, this study conducted true triaxial cyclic loading and unloading shear tests on intact and bedded limestone under different normal stress σnand lateral stress σpto investigate the shear strength, deformation, and failure characteristics. The results indicate that under different σnand σp, the stress–strain hysteresis loop area gradually increases from nearly zero in the pre-peak stage, becomes most significant in the post-peak stage, and then becomes very small in the residual stage as the number of shear test cycles increases. The shear peak strength and failure surface roughness almost linearly increase with the increase in σn, while they first increase and then gradually decrease as σpincreases, with the maximum increases of 12.9% for strength and 15.1% for roughness. The shear residual strength almost linearly increases with σn, but shows no significant change with σp. Based on the acoustic emission characteristic parameters during the test process, the shear fracture process and microscopic failure mechanism were analyzed. As the shear stress τincreases, the acoustic emission activity, main frequency, and amplitude gradually increase, showing a significant rise during the cycle near the peak strength, while remaining almost unchanged in the residual stage. The true triaxial shear fracture process presents tensile-shear mixture failure characteristics dominated by microscopic tensile failure. Based on the test results, a 3D shear strength criterion considering the lateral stress effect was proposed, and the determination methods and evolution of the shear modulus G, cohesion cjp, friction angle φjp, and dilation angle ψjpduring rockmass shear fracture process were studied. Under different σnand σp, Gfirst rapidly decreases and then tends to stabilize; cjp, φjp, and ψjpfirst increase rapidly to the maximum value, then decrease slowly, and finally remain basically unchanged. A 3D shear mechanics model considering the effects of lateral stress and shear parameter degradation was further established, and a corresponding numerical calculation program was developed based on 3D discrete element software. The proposed model effectively simulates the shear failure evolution process of rockmass under true triaxial shear test, and is further applied to successfully reveal the failure characteristics of surrounding rocks with structural planes under different combinations of tunnel axis and geostress direction.

There is limited applicability to the current method for testing the direct tensile strength of rocks because it places stringent requirements on the testing equipment. This work suggests a universal method based on the “compression-to-tension” idea in response to these difficulties. By applying pressure, this technique makes it possible to test the tensile strength of rocks directly with any conventional compression test machines. Granite was utilized as the test material in order to validate this suggested testing method, and the results showed what follows. Upon determining the true fracture area through digital reconstruction, an average calculated tensile strength of 5.97 MPa with a Cvof 0.04 was obtained. There is a positive correlation between tensile strength and the joint roughness coefficient (JRC) of the failure surface. The aggregation mode of AE events with the loading process conforms to the damage characteristics of rock tensile failure. The direct tensile testing method proposed in this study not only has high universality but also produces test results with outstanding consistency. Additionally, factors influencing the results of the tensile test are pointed out, and recommendations for optimizing the suggested testing method are offered.

To investigate the strength characteristics and failure mechanism of granite after thermal treatment are critical for geothermal energy storage and development. Acoustic emission (AE) is widely used to deduce the process of rock crack generation, development and penetration in laboratory tests, thus revealing the mechanism of rock failure. However, previous investigations have shown that laboratory tests cannot directly observe the interaction of thermal cracks and thermal stress, and more than 90%of AE tensile failure sources cannot be captured. This paper investigates the generation mechanism of thermal cracks and thermal stress distribution in thermally treated specimens using the discrete element method. After that, the evolution of AE failure sources is quantitatively analyzed by the moment tensor inversion results. The results showed that: (1) Thermal cracks destroy the internal structure of the specimen, thus weakening its mechanical properties. The number of thermal cracks increases with the temperature, further aggravating the damage to the mechanical properties of specimens; (2) as the temperature increases, the failure mode of the specimen changes from splitting failure to shear failure. Moment tensor inversion revealed that tensile failure dominated the final damage of samples. The shear and compaction failure sources increase with temperature, while tensile failure sources decrease; (3) the bvalue increased by 215%from 25 ∘C to 1000 ∘C. As the number of microcracks in a single AE event increases, the AE frequency decays exponentially, and most AE events have 1–5 microcracks.

Shale reservoir is the research hotspot in the development of unconventional oil and gas resources. The properties of bedding plane have an important influence on the mechanical behavior of shale. According to the fracture characteristics of layered shale under Brazilian splitting load, the effects of bedding angle, bond strength ratio and natural fractures on the tensile strength and fracture pattern of layered shale in Brazilian splitting test were studied by particle flow code. The evolution mechanism of meso–macro fracture of shale is analyzed by combining the dynamic change process of particle mesoscopic force chain and crack. The results show that three types of fracture patterns are observed: splitting tensile failure of shale matrix, splitting tensile failure along bedding plane and tensile–shear composite failure along shale matrix and bedding plane. Mesoscopic cracks initiate at the top and bottom loading points of the disk. After the peak load, mesoscopic cracks propagate through and appear dense force chains until macroscopic failure occurs. The bond strength ratio of bedding plane affects the failure pattern and peak strength of the specimen. With the increase in bedding angle, the tensile strength decreases gradually. Considering the influence of natural fractures, the tensile strength of shale is lower, and the crack propagation is more complex. The research model and results provide theoretical basis for the mechanical properties evaluation and fracture pattern analysis of shale.

A crystal plasticity model based on Electron Backscatter Diffraction (EBSD) experimental data has been developed to simulate the tensile behavior of additively manufactured TiAl alloys at various temperatures. To accurately capture the activity of different slip systems and their contribution to the material's plasticity, multiple slip systems across different phases are considered. The validity of the model is verified by comparing the simulation results, such as microscopic properties, with experimental and test data. Additionally, a continuous damage model is incorporated to analyze the damage behavior of additively manufactured TiAl alloys at different temperatures. Compared to experimental data, the crystal plasticity model incorporating damage effectively simulates the tensile failure behavior of TiAl alloys across a range of temperatures.

Biodegradable polylactic acid (PLA) melt-blown nonwovens are attractive candidates to replace non-degradable polypropylene melt-blown nonwovens. However, it is still an extremely challenging task to prepare PLA melt-blown nonwovens with sufficient mechanical properties for practical application. Herein, we report a simple strategy for the large-scale preparation of biodegradable PLA/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) melt-blown nonwovens with high strength and excellent toughness. In this process, a small amount of PHBV is added to PLA to improve the latter’s crystallization rate and crystallinity. In addition, when the PHBV content increases from 0 to 7.5 wt%, the diameters of the PLA/PHBV melt-blown fibers decrease significantly (with the proportion of nanofibers increasing from 7.7% to 42.9%). The resultant PLA/PHBV (5 wt% PHBV) melt-blown nonwovens exhibit the highest mechanical properties. The tensile stress, elongation, and toughness of PLA/PHBV (5 wt% PHBV) melt-blown nonwovens reach 2.5 MPa, 45%, and 1.0 MJ·m−3, respectively. More importantly, PLA/PHBV melt-blown nonwovens can be completely degraded into carbon dioxide and water after four months in the soil, making them environmentally friendly. A general tensile-failure model of melt-blown nonwovens is proposed in this study, which may shed light on mechanical performance enhancement for nonwovens.

Epoxy insulators are subjected to complicated mechanical stresses as well as strong electric field, resulting in frequent breakdown faults in gas-insulated transmission line (GIL). In this study, the synergic effects of biaxial stresses on electrical tree growth are investigated by pulling and compressing the epoxy samples in two perpendicular directions. Results show that tensile stress promotes the electrical tree growth, while compressive stress plays the role of suppressing first and then promoting as the stress value increases. That is, the relation between biaxial stresses is not only a competition but also a cooperation. The mathematical relations between the biaxial stresses and the tree growth rate are obtained by correlation analysis, and the energy model of brittle materials is proposed to explain the underlying mechanism, i.e., the tensile failure model for the competitive relation and the shear failure model for the cooperative relation. The energy model of epoxy resin is established quantitatively, and it is in good agreement with the experimental data. The outcomes of this study are hoped to provide references for the insulation design and material modification in UHV projects.