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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.

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.

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.

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.

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.

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.

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.

The study presented in this paper discusses a discontinuum-based model for investigating strength and failure in sedimentary rocks. The model has been implemented by UDEC to incorporate an innovative orthotropic cohesive constitutive law for contact. To reach this purpose, a user-defined model has been established by creating dynamic link libraries (DLLs) and attaching them into the code. The model reproduces rock material by a dense collection of irregular-sized deformable particles interacting at their cohesive boundaries which are viewed as flexible contacts whose stress-displacement law is assumed to control the fracture and the fragmentation behaviours of the material. The model has been applied to a sandstone. The individual and interactional effects of the microstructural parameters on the material compressive and tensile failure responses have been examined. In addition, the paper presents a new methodical calibration procedure to fit the modelling microparameters. It is shown that the model can successfully reproduce the rock mechanical behaviour quantitatively and qualitatively. The study also shows how discontinuum-based modelling can be used to characterize the relation between the microstructural parameters and the macro-scale properties of a material.

Tensile failure mechanisms in type I carbon fibre-reinforced epoxy resin have been studied by examining the modes of failure of cured and semi-cured CFRP and of fibre bundle specimens. The rigid matrix in the cured material modified the appearance of the fractured specimen but by detecting the acoustic emission generated during loading the basic fibre bundle behaviour was found to exert a major influence on fracture. Microscopic examination of fractured CFRP specimens has revealed that consecutive fibre failure may be restricted to sub-bundles as a result of shearing between these sub-bundles, and that the material is weakened by a number of internal failures that are not necessarily connected. Ultimate failure seems to be statistically determined and it is a characteristic of the material that some scatter in the strength of CFRP must be expected.

Variation of critical cut lengthIc in tensile failure of rubber vulcanizates has been studied with respect to the following variables: addition of short silk fibre, fibre concentration and orientation, ageing, reinforcing carbon black filler and elevated temperature. Strain crystallizing rubbers, e.g. natural (NR) and polychloroprene (CR), show higherIc values than non-strain crystallizing nitrile rubber (NBR). The addition of short fibres was found to cause an increase inIc in all cases. The increase is more prominent in the case of NBR than for NR and CR. TheIc values for unfilled NBR vulcanizates are low and a marginal increase is noted on the addition of carbon black. Addition of short fibres leads to a significant improvement in theIc values, which show a gradual increase with increase in fibre concentration in the composites.Ic exists only in the composites wherein the fibres are oriented along the direction of application of tensile stress rather than across it, and the decrease in tensile strength is marginal at the initial stages but a sharp fall is observed with increasing size of cut lengths. On ageing,Ic values for composites increase while those for unfilled vulcanizates decrease. Critical cut length values for the fibre reinforced composites at a higher temperature (e.g. 100° C) remained unchanged, but dropped in the case of unfilled vulcanizates.

Scanning electron microscopy and acoustic emission are used to investigate the initial stages of tensile failure in unflawed polycrystalline alumina. It is found that deformation twinning plays an important role in crack initiation even at low homologous temperatures, and that the temperature-dependent strength behaviour between 23 to 410° C is controlled by twinning.

Abstract: The tensile failure strength of ceramic composites can be measured by tests in bending or in tension, but care must be exercised over the experimental conditions. The strength values obtained are dependent on the test method and specimen size. It is shown that differences between strengths measured in bend and tensile tests can be understood in terms of the statistical distribution of the strengths of individual fibres.

Results are discussed from experimental and theoretical studies on the tensile failure of short, steel fiber‐reinforced mortar/concrete (SFRC) composites. A displacement‐controlled test method for conducting stable fracture tests on tension‐weak brittle materials developed in an earlier study has been used for conducting uniaxial tension tests. Several concrete, mortar, paste, and SFRC mixes were tested. Fracture of SFRC in tension is observed to be influenced largely by the matrix softening behavior, the fiber‐matrix interfacial response, and its composition parameters. The theoretical model proposed for the idealized SFRC composite takes into account these two primary nonlinear aspects of the failure mechanism in such composites, i.e.: (1) The inelastic behavior of the fiber‐matrix interface; and (2) the softening characteristics of the matrix. The model, in addition, is also realistically sensitive to the reinforcement parameters like fiber volume content, aspect ratio, and the elastic properties of the fiber.

The mechanical properties of one of the new high strength polymer modified hydraulic cements have been investigated. An important parameter for the material is the amount of polymer present, and the properties are found to be dependent upon the degree of drying. For example, in the wet state, polymer content has little effect upon ultimate flexural strength, but does cause nonlinearity in the stress-strain behaviour. Although increasing polymer content causes a reduction in the initial tangent modulus, it is shown that retardation of hydration may account for this. In the dry state, increasing polymer content leads to increasing flexural strength, fracture toughness and failure strain, but leaves initial elastic modulus relatively unchanged. It is concluded that removal of pores is not the principal strengthening mechanism since strength increases are consequent upon water removal from the microstructure in the presence of the polymer. A fibrillar pull-out model is proposed to explain the observed behaviour of both “wet” and “dry” material and ordinary Portland cement paste, which shows good correlation with experimental results. The principal effect of the polymer is to act as an adhesive at the interface between interacting CSH fibrils.

The ultimate tensile behaviour of fibre-reinforced cementitious composites is closely related to its failure mechanisms which in turn are dependent on reinforcement parameters such as fibre characteristics and the fibre/matrix interface properties. Based on the direct tensile tests of mortar specimens reinforced with various synthetic fibres, this paper attempts to explain such relationships and to indicate directions towards more effective fibre reinforcement.

The potential of the acoustic-ultrasonic stress-wave factor as a non-destructive testing technique for unidirectional carbon-fibre-reinforced polypropylene composite laminates has been investigated. The stress-wave factor is found to be a sensitive indicator of strength variation in these composites, and increases in proportion to fractional powers of the ultimate tensile strength. The lowest value of the stress-wave factor also correlates well with the fracture on the specimen. This method is also sensitive to strength variations associated with porosity and differences in the fibre: resin ratio.

This paper presents a theoretical treatment of the tensile strength of a unidirectional fibrous composite, subjected to a tensile load in the fibre direction. The fibres are treated as having a statistical strength distribution which results in fibre failure prior to composite failure. The failure geometry of the model is similar to the observed geometry of fractured glass/epoxy and glass/polyester composites. Failure criterion is established and the strength is shown to decrease as the length of the specimen is increased. This size effect is very small.

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.

The dynamic response and failure characteristics of tunnels vary significantly under various dynamic disturbances. These characteristics are crucial for assessing structural stability and designing effective support for surrounding rock. In this study, the theoretical solution for the dynamic stress concentration factor (DSCF) of a circular tunnel subjected to cylindrical and plane P-waves was derived using the wave function expansion method. The existing equivalent blast stress wave was optimized and the Ricker wavelet was introduced to represent the seismic stress waves. By combining Fourier transform and Duhamel’s integral, the transient response of the underground tunnel under near-field blasts and far-field earthquakes was determined in both the frequency and time domains. The theoretical results were validated by comparing them with those obtained from numerical simulations using ANSYS LS-DYNA software. Numerical simulations were conducted to further investigate the damage characteristics of the underground tunnel and evaluate the effect of initial stress on structural failure under both types of disturbances. The theoretical and numerical simulation results indicated that the differences in the dynamic response and damage characteristics of the underground tunnel were primarily due to the curvature of the stress waves and transient load waveform. The locations of the maximum DSCF values differed between near-field blasts and far-field earthquakes, whereas the minimum DSCF values occurred at the same positions. Without initial stress, the blast stress waves caused spalling damage to the rock mass on the wave-facing side. Shear failure occurred near the areas with maximum DSCF values, and tensile failure occurred near the areas with minimum DSCF values. In contrast, damage occurred only near the areas with maximum DSCF values under seismic stress waves. Furthermore, the initial stress exacerbated spalling and shear damage while suppressing tensile failure. Hence, the blast stress waves no longer induced tensile failure on the tunnel sidewalls under initial stress.

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.

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.

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.

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.

Weak interlayers play a crucial role in the seismic performance of bedding slopes; however, the effects of structural surface development within these layers remain underexplored. This study presents two scaled models of bedding slopes, each with different weak interlayers: one with a homogeneous weak layer and another with discontinuous interfaces. Shaking table tests were conducted to compare their seismic performance. The results show that the peak ground acceleration (PGA) values above the weak interlayer in model A were significantly higher than those in model B, with the differences increasing as the input wave amplitude increased. The peak earth pressure (PEP) values at the tensile failure boundary at the rear edge of model A were also higher, whereas those within the weak layer at the toe of model A were lower than those in model B. Deformation analysis revealed that the maximum principal strain in model A initially appeared at the upper part of the tensile failure boundary, while the maximum shear strain was concentrated near the rear edge within the weak layer. In contrast, model B exhibited the opposite strain distribution. These findings provide insight into the impact of weak interlayers on the dynamic response and deformation of bedding slopes, highlighting the importance of considering this factor in seismic landslide investigations and failure mode predictions.

An innovative critical plane determination approach with weight-averaged largest fatigue damage is proposed, in which the material failure modes can be considered. If material exhibits shear cracking behavior, a strain-based critical plane model with shear failure mode is selected to evaluate the weight function. Otherwise, other one with tensile failure mode is adopted. According to the proposed critical plane, a multiaxial fatigue lifetime estimation methodology is established for evaluating fatigue life. And, six kinds of materials are employed to validate the validity of presented methodology. The validation results reveal the presented methodology can estimate the orientation angles of failure plane accurately and supply satisfactory fatigue lifetime estimations for both shear and tensile failure mode materials. Furthermore, the proposed critical plane framework can be extended to be utilized with stress-based fatigue criteria, and prediction results show a good agreement with experimental data by another two materials.

The number of layers and ply orientations determined the service performance of carbon fiber-reinforced polymer (CFRP) materials. Under low-temperature service conditions, the unclear weakening mechanism of mechanical properties of CFRP aggravates the failure risks of aerospace structures. In present work, the unclear correlation between layers with alternating orientations and the tensile-failure mechanisms of CFRP, the low temperature-mechanical coupling micromechanical behavior, and the failure mechanism of CFRP was experimentally revealed by using a horizontal testing instrument integrated with a low-temperature loading module and real-time optical imaging function. Based on various temperatures in a range from −40 °C to room temperature (RT) and two strain rates, the gradually decreasing trends of tensile strength, Young's modulus, and elongation after fracture with decreasing temperature are obtained. Three failure modes including fiber brittle fracture, fiber pull-out, and interface debonding are proposed to reveal the low temperature-mechanical coupling failure mechanism. Low-temperature asynchronous shrinkage of carbon fiber and epoxy resin promoted the transition from fiber brittle fracture to delamination at the interface. The proposed instrument could establish the approximatively actual service conditions involving low temperature and mechanical load.

To determine the relationship between slabbing failure and the specimen height-to-width (H/W) ratio and to analyze the conditions, characteristics, and mechanism of slabbing failure in the laboratory, uniaxial compression tests were conducted using six groups of granite specimens. The entire failure process was recorded using strain gauges and high-speed cameras. The initiation and propagation of fractures in specimens were identified by analyzing the monitoring results of stress, strain, and acoustic emission. The experimental results show that changes in the specimen H/Wratio can transform the macro failure mode. When the H/Wratio is reduced to 0.5, the macro failure mode is dominated by slabbing. Low load-bearing ability is observed in specimens with slabbing failure, and the slabbing fractures are approximately parallel to the loading direction. Moreover, the fracture propagation characteristics and acoustic emission signals of slabbing failure specimens show typical tensile failure characteristics, indicating that slabbing failure is essentially a special tensile failure.

To explore the chemical and mechanical effects of acid mine drainage on water and rock, acid mine drainage (AMD) dissolution tests, triaxial compression tests, and acoustic emission tests were performed on limestone rock samples with different bedding dip angles. Combined with scanning electron microscopy and nuclear magnetic resonance analyses, the changes in the internal pores and surface morphologies of the rock samples before and after dissolution were analyzed. The results were as follows. (1) AMD dissolution mainly occurred in the shallow surfaces and bedding planes of the limestone samples. During dissolution, the shape of the matrix crystal disappeared to form small pores, and residual substances appeared during the dissolution of the bedding plane. These small pores were prone to the creation of large honeycomb-like dissolved pores. (2) With increasing bedding plane angle, the compressive strengths and elastic moduli of the limestone samples exhibited V-shaped distributions. Additional branch cracks were derived from the limestone samples after dissolution, and dissolution reduced the mechanical strength of the limestone by decreasing the crack initiation stress and damage stress. (3) With increasing bedding dip angle, the uniaxial failure modes of the rock samples changed from matrix tensile failure and shear failure along the bedding plane to plane tensile failure. After dissolution, the limestone matrix was prone to cracking and spalling along the surface of the sample. (4) There were differences in the triaxial compression failure modes between the dissolved limestone and the undissolved limestone. When α = 0° or 90°, the limestone samples formed additional branch fissures after dissolution. When α = 45°, the formation of penetrating cracks along the bedding plane was obviously controlled by the bedding plane. (5) A chemical–mechanical damage model was established and modified by the compression coefficient K, which could effectively reflect the deformation of the dissolved rock sample during loading.

This article was designed with a plurality of impact tests of three-dimensional four-directional braided composites, and the impact response of specimen impacted by a circular punch was studied. Ultrasonic C-scanning was used to detect the internal damage area to study the damage propagation process under multiple impact loads. The finite-element software ABAQUS was used to model the meso-structure of three-dimensional four-directional braided composites. Based on material characteristics, the three-dimensional Hashin damage criterion was used for the fiber bundle, and the maximum stress criterion was used for the matrix to judge the material damage. Combined with test and simulation results, the failure mode and damage evolution process of the specimen under multiple impact loads were studied. The results showed that the impact resistance of the three-dimensional woven composite material is affected by the braided angle. The larger the braided angle of the specimen, the better the impact resistance. The damaged area of the large braided angle material expanded to the periphery, and the damaged area of the small braided angle material was primarily developed in the longitudinal direction. The failure modes of the specimen during the impact process were primarily a longitudinal tensile failure of fiber bundles, transverse tensile failure and transverse compression failure of fiber bundles and matrix.

Fiberglass-reinforced ultraviolet cured-in-place pipe (UV–CIPP) composite material is one of the most trenchless materials for underground pipelines’ rehabilitation. In this paper, the bending resistance and damage evolution mechanism of glass fiber-reinforced UV-CIPP composites were investigated under the influence of glass fiber structure, the number of layers of glass fibers, the angle of fiber layups, and the thickness of the material by high-definition video, SEM and infrared thermal imaging. The results indicate that the damage evolution modes of UV-CIPP materials mainly include: (1) fiber pull-out and overall fiber bundle tensile failure caused by strong interfacial bonding, (2) fiber/matrix debonding and delamination, fiber fracture, and matrix cracking caused by weak interfacial bonding. Furthermore, among the seven different fiberglass structures of UV-CIPP materials, the [0°/90°] warp-knit axial/short-cut felt fiberglass fabric exhibit the best flexural performance, with a bending strength of 412 MPa and a bending modulus of 16.1 GPa for the 4 layers glass fiber fabric. Moreover, in the bending process of UV-CIPP materials, the surface temperature rises primarily due to fiber break, the temperature transition aligning with the stress transition. Finally, the energy release is mainly caused by the failure of the glass fibers, but the resin contributed comparatively little. This study provides a scientific reference for the structural design and optimization of UV-CIPP materials.

In order to understand the mechanical properties and the fracture surface roughness characteristics of thermally damaged granite under dynamic splitting, dynamic Brazilian splitting tests were conducted on granite samples after thermal treatment at 25, 200, 400, and 600°C. Results show that the dynamic peak splitting strength of thermally damaged granite samples increases with increasing strain rate, showing obvious strain‐rate sensitivity. With increasing temperature, thermally induced cracks in granite transform from intergranular cracks to intragranular cracks, and to a transgranular crack network. Thermally induced damages reduce the dynamic peak splitting strength and the maximum absorbed energy while increasing the peak radial strain. The fracture mode of the thermally damaged granite under dynamic loads is mode II splitting failure. By using the axial roughness index Z2a${Z}_{2}^{{\rm{a}}}$, the distribution ranges of the wedge‐shaped failure zones and the tensile failure zones in the fracture surfaces under dynamic Brazilian splitting can be effectively identified. The radial roughness index Z2r${Z}_{2}^{{\rm{r}}}$is sensitive to the strain rate and temperature. It shows a linear correlation with the peak splitting strength and the maximum absorbed energy and a linear negative correlation with the peak radial strain. Z2r${Z}_{2}^{{\rm{r}}}$can be used to quantitatively estimate the dynamic parameters based on the models proposed. The effects of thermal damage and the loading rate on dynamic splitting mechanical properties and fracture surface morphological characteristics of granite were determined. The surface roughness index Z2in the axial and radial directions of the Brazilian splitting sample was calculated. Prediction models of dynamic splitting parameters based on Z2r${{Z}_{2}}^{r}$are proposed. The effects of thermal damage and the loading rate on dynamic splitting mechanical properties and fracture surface morphological characteristics of granite were determined.The surface roughness index Z2${Z}_{2}$in the axial and radial directions of the Brazilian splitting sample was calculated.Prediction models of dynamic splitting parameters based on Z2r${Z}_{2}^{{\rm{r}}}$are proposed. The effects of thermal damage and the loading rate on dynamic splitting mechanical properties and fracture surface morphological characteristics of granite were determined. The surface roughness index Z2${Z}_{2}$in the axial and radial directions of the Brazilian splitting sample was calculated. Prediction models of dynamic splitting parameters based on Z2r${Z}_{2}^{{\rm{r}}}$are proposed.

• Establish a nonlocal friction model for analyzing the interaction between closed crack surfaces. • Implement surface contact algorithms with different inclination angles. • Study the effect factors of the initiation and propagation of wing cracks. • Increasing the friction coefficient or crack inclination angle will reduce the crack initiation angle and path length. To investigate the influence of the interaction between closed crack surfaces on crack propagation, a nonlocal friction contact model is proposed for numerical simulation of wing crack propagation under uniaxial compression. The closed cracks with different inclination angles are defined by mathematical models, and cracks are generated by breaking off bonds at specific positions. In terms of numerical model validation, the comparison with FEM results indicates the correctness of the friction contact numerical model. Subsequently, the maximum principal stress criterion was applied to determine the breakage of the bond. The simulation results showed that under uniaxial compression, the closed crack tips undergo tensile failure, and the wing cracks will gradually expand towards the direction of the maximum principal stress. Both the crack inclination angle α and friction coefficient f c have an impact on crack initiation and propagation, increasing α or f c will reduce the initiation angle θ of crack propagation. At the same inclination angle α, the larger the friction coefficient f c , the shorter the crack propagation length, while the smaller the inclination angle α, the more significant the influence of friction coefficient f c on the initiation angle θ and crack path. [ABSTRACT FROM AUTHOR]

Efforts to achieve a defect-free flat groove in near-surface-mounted prestressed fiber-reinforced polymer (FRP) strengthening systems have proven challenging. Despite attempts, attaining an ideal groove remains formidable. In this system, anchorage device installation involves injecting epoxy resin into groove defects to achieve planarity. Structural behavior analysis and optimization of the anchorage device were conducted based on device type, anchor type, and defect depth through shear loading tests. The mechanical anchor demonstrated an ultimate load of 261 kN, with failure modes including concrete cracking, concrete compression failure, and anchor tensile failure. The chemical anchor exhibited an ultimate load of 390 kN, with its final failure attributed to anchor tensile failure. The ultimate load capacity of anchorage device surpassed that of a carbon FRP(CFRP) bar by up to 62.5%. In a parametric study, the shear strength of the anchorage device was explored concerning concrete compressive strength and anchor diameter. The ultimate load of the proposed model with low concrete compressive strength proved insufficient compared to the strength of CFRP rebar.