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The existence of cracks is a key factor affecting the strength of concrete. However, traditional numerical methods still have some limitations in the simulation of crack growth in fissured concrete structures. Based on this background, the numerical treatment method of particle failure in smoothed particle hydrodynamics (SPH) is proposed, and the generation method for concrete meso-structures under the smoothed particle hydrodynamics (SPH) framework is developed. The concrete meso-models under different pre-existing micro-fissure inclinations and bridge angles (the inner tip line of the double pre-existing micro-fissure is defined as a bridge, and the angle between the bridge and the horizontal direction is defined as the bridge angle) were established, and numerical simulations of the crack propagation processes of concrete structures under tensile stress were carried out. The main findings were as follows: The concrete meso-structures and the pre-existing micro-fissures all have great impacts on the final failure modes of concrete. The stress–strain curve of the concrete model presents four typical stages. Finally, the crack initiation and propagation mechanisms of fissured concrete are discussed, and the application of smoothed particle hydrodynamics (SPH) in crack simulations of fissured concrete is prospected. [ABSTRACT FROM AUTHOR]

Complex coupled thermo-hydromechanical (THM) loading paths are expected to occur in clay rocks which serve as host formations for geological radioactive waste repositories. Exothermic waste packages heat the rock, causing thermal strains and temperature induced pore pressure build-up. The drifts are designed in such a way as to limit these effects. One has to anticipate failure and fracturing of the material, should pore pressures exceed the tensile resistance of the rock. To characterise the behaviour of the Callovo-Oxfordian claystone (COx) under effective tension and to quantify the tensile failure criterion, a laboratory program is carried out in this work. THM loading paths which correspond to the expected in situ conditions are recreated in the laboratory. To this end, a special triaxial system was developed, which allows the independent control of radial and axial stresses, as well as of pore pressure and temperature of rock specimens. More importantly, the device allows one to maintain axial effective tension on a specimen. Saturated cylindrical claystone specimens were tested in undrained conditions under constrained lateral deformation and under nearly constant axial stress. The specimens were heated until the induced pore pressures created effective tensile stresses and ultimately fractured the material. The failure happened at average axial effective tensile stresses around 3.0 MPa. Fracturing under different lateral total stresses allows one to describe the failure with a Hoek–Brown or Fairhurst's generalized Griffith criterion. Measured axial extension strains are analysed based on a transversely isotropic thermo-poroelastic constitutive model, which is able to satisfactorily reproduce the observed behaviour. Highlights: Thermal pressurization of clay rock in deep radioactive waste repositories can reduce the effective stresses, which can lead to damage or failure. Our novel laboratory triaxial device is able mimic in situ conditions: Constant vertical total stress, zero lateral deformation and thermal pressurization. Pore pressure increase, vertical extension strains and thermal pressurization failure were recorded in a series of tests on Callovo-Oxfordian claystone specimens. The effective tensile strength was reached at values around 3 MPa in tension and temperatures between 53 and 64 °C, creating sub-horizontal fractures. The experimental responses can be well reproduced using a thermo-poroelasticity model. Hoek–Brown and Fairhurst generalized Griffith criteria appear suitable to account for the rock's tensile resistance. [ABSTRACT FROM AUTHOR]

Purpose: The influence of the number and arrangement of bolts on the tensile properties of bolted composite laminates was studied in the present study. Design/methodology/approach: Based on the finite element model, the stiffness degradation method is used to simulate the damage evolution process for the failure of bolted composite laminates. Using ABAQUS finite element software combined with material failure criteria, the numerical calculation of the connection strength and failure mode of bolted composite laminates was carried out. Findings: The results of the study show that the tensile strength of the composite laminates connected by three bolts is higher than that of the laminates connected by two bolts. And the arrangement of different bolts has a great influence on the failure strength of bolted laminates. Originality/value: Bolted connection of composite laminates is a common problem in engineering practice. The effect of bolt arrangement and number on the strength of composite laminates is studied in this manuscript. [ABSTRACT FROM AUTHOR]

• Efficient strain predictions are achieved with DeepLabv3+, enhancing the speed and accuracy of structural analysis. • Rapid and precise failure mode determinations are made possible by VGG-16, employing focal loss for efficient classification. • Accurate interpretability is ensured through Grad-CAM, aligning neural focus areas with fracture mechanics theory. • The method significantly improves efficiency, providing quick and confident results without the need for labor-intensive re-modeling during the FEA process. The joint is a critical component that facilitates force transmission across precast bridge slabs while maintaining structural integrity. Finite Element Analysis (FEA) is commonly used to examine the mechanical properties and load-bearing capacity of joints with different configurations. However, the repetitive process of "modeling-meshing-computing" consumes substantial manpower, time, and expertise. This study proposes an approach consisting of three key steps: (1) predicting strain distributions, (2) determining failure modes, and (3) analyzing interpretability of predicted results. Specifically, DeepLabv3+ is used to map the Finite Element (FE) model to strain distributions. A binary classification model based on VGG-16 predicts the failure state of the specimen. Interpretability analysis, using Gradient-weighted Class Activation Mapping (Grad-CAM), provides insights into the neural network's decision-making process. The optimized models achieve a Mean Intersection over Union (MIoU) of 0.5691 for strain distribution prediction on the cross-sectional surface and 0.6424 on the front surface. The failure detection model achieves an F1 score of 0.992 in determining failure states. The interpretability results align well with fracture mechanics theory, enhancing confidence in the model's predictions. This method serves as a surrogate to reduce the workload of finite element analyses, facilitating strain analysis and failure detection. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach for modeling the tensile failure of quasi-brittle materials by incorporating a multivariate random field to represent material parameters in the phase field model. The aim is to characterize and propagate uncertainties in the behaviors of materials, taking into account the spatial variability and probabilistic dependence. Copula theory is employed to investigate the probability distributions and dependence configuration of the parameters. The proposed framework combines the generation approach for the multivariate random field with the phase field model, resulting in a complete numerical analysis methodology. The governing equations of the deterministic phase field model for quasi-brittle solids are outlined, followed by a description of the multivariate random field for quasi-brittle media and its uncertainty characterization procedure using copula theory. A numerical approach for generating samples of the multivariate random field is introduced. The numerical analysis procedure for the tensile fracture of concrete is presented, and the effects of material uncertainties on failure patterns and macroscopic responses are discussed. The results demonstrate that the developed methodology effectively captures the random damage and fracture processes in concrete specimens. The interaction between the correlation length of the random field and the characteristic length scale of the phase field significantly influences the probabilistic characteristics of the random responses. The research findings emphasize the importance of determining the correlation length values accurately. This study contributes to the field of structural reliability analysis by providing a comprehensive framework for modeling the stochastic behavior of quasi-brittle materials. The integration of a multivariate random field and copula theory allows for the realistic representation of material uncertainties and their probabilistic dependence. The proposed methodology, combined with the probability density evolution method (PDEM), offers a powerful tool for analyzing and predicting the probabilistic evolution of material behaviors under tensile loading conditions. [ABSTRACT FROM AUTHOR]

• For some materials and conditions failure mechanism can change from shear in Low Cycle Fatigue to tensile in High Cycle Fatigue. • A modified form of the FS parameter recently proposed by Gates and Fatemi is able to capture the failure mechanism transition. • A wide range of materials from the literature with failure mechanism change are evaluated based on the modified parameter. Depending on several factors, the failure mechanism can change with life for a particular material, from shear in Low Cycle Fatigue (LCF) to tensile in High Cycle Fatigue (HCF). Critical plane-based approaches to multiaxial fatigue have the capability of reflecting the damage mechanisms of the material and can, therefore, not only provide fatigue life estimation under different stress states, but also predict the highest damage (i.e., critical) plane orientation. While Fatemi-Socie critical plane parameter has been used extensively in the literature for many materials with shear failure mechanism, a modified form of the parameter recently proposed by Gates and Fatemi is shown to also be able to capture the failure mechanism transition from shear in LCF to tensile in HCF. The mechanisms by which this parameter accounts for the transition from shear to tensile is discussed in this work. A wide range of materials from the literature with failure mechanism change from shear in LCF to tensile in HCF are evaluated based on this parameter. [ABSTRACT FROM AUTHOR]

This paper proposes a three-dimensional failure criterion model for unidirectional fiber-reinforced composites. In contrast to previous models that only accounted for the effect of fiber misalignment in the presence of longitudinal compressive stress, the proposed failure criterion model comprehensively considers the effect of localized misaligned regions on the failure under any stress state. Another key contribution of this study is the introduction of the effective misalignment angle. Considering effective misalignment angles, the proposed failure criterion model can reasonably reveal the effect of localized misaligned regions on the failure behavior under different stress states. The agreement between the predicted results and the experimental data proves that the proposed model has good applicability. Furthermore, the influence of initial misalignment angles on failure is analyzed under varying stress conditions. The results indicate that even under longitudinal tensile stress, the initial misalignment angle still plays an important role in the failure behavior of materials. [Display omitted] • A three-dimensional failure model considering fiber misalignment is proposed. • The traditional method for determining the misalignment angle is corrected. • Fiber misalignment has an effect on material failure under longitudinal tensile stress. • The influence of the initial misalignment angle on failure is analyzed. [ABSTRACT FROM AUTHOR]

The paper presents the experimental and numerical study of the failure behaviour of Fused Filament Fabricated (FFF) Polylactic Acid (PLA) samples subjected to tensile load. The examined samples are printed in flat orientation with 0°, 45° and 90° raster angles. During the experiments the deformation of the specimens is continuously scanned with the 3D Aramis measuring system utilizing the digital imaging correlation technique, enabling the determination of strain and stress distribution. In the modelling, it is assumed that each printed layer is a homogeneous transversely isotropic medium with the raster direction treated as the favoured one. The finite element models are developed in the Abaqus-Standard package. A two-dimensional equivalent single-layer approach is utilized to describe the deformation and stress state of the samples. The failure progress of the material is simulated by making use of the Hashin damage algorithm with energy-based softening, whereas the non-linear in-plane shear behaviour is included. • Experimental and numerical failure study of 3D printed PLA sheets subjected to tensile load is performed. • The strain field of the specimens is scanned with the Aramis system with digital imaging correlation technique. • The simulations are performed in the Abaqus program by taking the advantage of the formalisms of the laminates modelling. • Advantages and limitations of the approach are discussed. [ABSTRACT FROM AUTHOR]

In this paper, failure mechanism of 20 carbon steel and QT400-15 specimens is in situ investigated by a microscope under combined torsion–tension loading (CTTL) at room temperature. Moreover, to obtain the effect of pre-torsional loading on the failure mechanism of materials under CTTL, a finite element analysis model is conducted to predict the specimen stress distribution. Results of theoretical calculation, finite element analysis, and experimental investigation indicate that the pre-torsional strain of materials is increased with an increase in the pre-torsional loading angle. The pre-torsional strain refined the material grains under CTTL, which in turn slowed down the crack growth. Consequently, material tensile strength is improved under CTTL. The in situ images effectively characterized grain refinement of materials under pre-torsional loading. Furthermore, the failure mechanism of materials under CTTL is different from the mechanism under pure tension loading, which was characterized by intergranular material fracture. However, the material fracture under CTTL was characterized by both transgranular and intergranular fractures. [ABSTRACT FROM AUTHOR]

For solving the computationally intensive problem encountered by the discrete element method (DEM) in simulating large-scale engineering problems, it is essential to establish a numerical model that can effectively simulate large-scale rocks. In this study, the coarse-graining effect of a linear-Mindlin with bonding model was studied in the unconfined compression strength (UCS) and Brazilian tensile strength (BTS) tests. We found that the main reason for the coarse-graining effect of the BTS tests is that the type I fracture toughness is positively correlated with the size of the particles. Based on the results analysis and fracture mechanics, the coarse-grained (CG) modeling theory was combined with a bonded particle model (BPM) for the first time and a coarse-grained bonded particle model (CG-BPM) was developed, which can be effectively used to model the tensile strength of large-scale rocks with different particle sizes. The excavation damage zone (EDZ) in an underground research laboratory (URL) was selected as an application case, which shows that the coarse-grained bonding model presented in this paper is more accurate and reliable than the traditional one in large-scale rock simulation, at least in the scenario where tensile failure is dominant. [ABSTRACT FROM AUTHOR]

Underground rock mass conditions are often complex, crack propagation and coalescence results in a reduction in rock strength and can cause brittle failure. We study the influence of the fluid pressure and the lateral pressure on the propagation process of parallel flaws, the failure mechanism of rock bridges and the rock failure modes, respectively. A lateral pressure loading device and a water injection system are designed for experimental analysis. A fracture-damage model is introduced in the continuous discontinuous discrete element method to describe the crack propagation process. The following conclusions are obtained: compared with the specimen without fluid pressure in the flaws, the fluid pressures (0.5 MPa, 1 MPa and 1.5 MPa) affect the rock bridge coalescence modes, strength characteristics and failure forms under uniaxial compression. With the increase of fluid pressure, the failure form of the rock bridge changes from tensile shear failure to tensile failure. Without fluid pressure in the flaws, tensile shear failure occurs in the rock bridge under uniaxial compression. With the increase in the lateral pressure coefficient (30%), wing crack growth is restrained, and shear cracks appear in rock bridges, causing the failure mode of the rock bridge changes from tensile shear failure to shear failure. Compared with the specimen without fluid pressure in the flaws, with the increase of fluid pressure, the tensile stress at the flaw tips increases, and the shear stress at the rock bridges decreases , which promotes the growth of tensile cracks and decreases the peak strength of the specimen. Especially, high-pressure fluid promotes the coalescence of rock bridges and cause tensile failure occurs in the specimen, resulting in more obvious brittle failure characteristics of the specimen than the specimen with low fluid pressure and without fluid pressure. Highlights: The propagation process of parallel flaws and the failure mechanism of rock bridges under different fluid pressures were investigated. The rock brittle failure characteristics and the initiation stress of the parallel flaws under the fluid pressure were analyzed. The improved fracture-damage model in the CDEM can well simulate crack propagation process under hydromechanical coupling. [ABSTRACT FROM AUTHOR]

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Studying the penetration characteristics of blast‐induced cracks during double water jet slotted boreholes blasting is theoretically and practically significant since it acts both by the "superposition effect" of explosion‐induced stress waves and the "guiding effect" of water jet slots. A combination of experimental testing and numerical simulation was adopted to investigate the transmission law of explosion‐induced stress waves and the propagation law of blast‐induced cracks first. Then the penetration characteristics of blast‐induced cracks was analyzed according to rock blasting theory and rock fracture mechanics theory. The results indicate that the rock between the two boreholes is mainly subjected to a tensile failure mode due to the combined effect of the "superposition effect" of explosion‐induced stress wave and the "guiding effect" of water jet slot during double water jet slotted boreholes blasting. The hole spacing significantly affects the penetration mode of blast‐induced cracks during double water jet slotted boreholes blasting, and unless it reaches a certain value, a single flat through‐crack will form between two slotted boreholes. In addition, when the blast‐induced cracks successfully penetrate each other, the hole spacing of double water jet slotted boreholes increases by 33.3% compared with that of double circular boreholes under the same conditions. The research results can provide guidance for the application of directional controlled blasting technology with water jet assistance. [ABSTRACT FROM AUTHOR]

Microwave energy and in situ stress cooperatively influence the permeability of coal reservoirs in microwave-assisted coalbed methane (CBM) extraction. In this study, the combined influence of microwave energy and load on the failure characteristics of coal reservoirs was investigated using acoustic emission (AE) technology. The failure characteristics of anthracite derived from microwave irradiation during uniaxial compression was analyzed from aspects such as the correlation dimension (D) of the AE time series, b-value, and AF–RA correlation. Then the combined mechanism of microwave energy and in situ stress was explored. The results indicated that microwave energy significantly affected the AE activity of anthracite under loading. Moreover, microwave irradiation lessened the damage intensity and increased the crush degree during loading. After low-energy microwave (≤ 90 kJ) irradiation, the AE signals of anthracite were active only in the unstable crack growth stage, with less damage under load, and mainly characterized by the rapid expansion of large fractures. In contrast, after high-energy microwave (> 90 kJ) irradiation, AE signals penetrate the entire loading process, and the required energy for damage decreased, mostly manifested as small-scale microcracks. Additionally, microwave irradiation changed the failure mode of anthracite under loading from shear failure to tensile failure. In summary, microwave thermal effect reduced the stress threshold for fracture propagation by improving the physical structure of coal reservoirs. Cracks initiated by microwave irradiation could cause in situ stress redistribution, forming stress reduction areas and stress concentration areas, thereby accelerating the expansion of fracture networks. Therefore, the results of this study have great significance for optimizing the scheme of microwave-assisted CBM extraction and improving the CBM production rate through effective utilization of in situ stress. Highlights: Microwave irradiation enhances the AE activity of anthracite under load. Microwave irradiation decreases the failure intensity and increases the damage degree of anthracite. Microwave irradiation changes the failure mode of anthracite from shear failure to tensile failure. The cooperative mechanism of microwave energy and in situ stress during microwave-assisted CBM extraction is discussed. [ABSTRACT FROM AUTHOR]

The symmetrical fissures located within the surrounding rock of the roadway (borehole) in tunnel engineering activities can easily induce damage and instability of the surrounding rock. Therefore, studying the impact of perforated symmetrical fissures on the mechanical properties of rock with a hole has significant practical significance. Based on indoor experimental results, conventional triaxial compression simulations were performed on symmetrical fissure-hole sandstone using PFC2D. The impact of the dip angle and length of symmetric fissures on the mechanical properties of the hole-containing sandstone was analyzed. Furthermore, the relationship between crack propagation and the macroscopic mechanical properties of the specimen was discussed. The results show that: (1) The deterioration effect of symmetric fissures on hole-containing sandstone can be controlled by increasing the fissure dip angle, suppressing the stress drop phenomenon. However, increasing the fissure length exacerbates the deterioration effect. (2) The effect of symmetrical fissure dip angle on the displacement field near the hole decreases with increasing dip angle while increasing fissure length exacerbates the effect of fissures on the displacement field. (3) As the angle between the fissure and the vertical principal stress increases, the degree of tensile failure weakens while the degree of shear failure increases. (4) During the crack development phase, the extension of the stress concentration zone drives rapid crack growth. It exhibits a stress drop in the macroscopic mechanical properties, followed by the evolution of the stress field with loading, allowing rapid expansion of the microcracks and eventually leading to rock destabilization damage. [ABSTRACT FROM AUTHOR]

2.5D woven structures are of interest in new thermal protection systems for their excellent interlayer properties and structural stability. In this paper, dense (CDP) and lightweight (CLP) carbon/phenolic 2.5D woven composites were prepared. Quasi‐static tensile experiments were performed on the specimens before ablation (TCDP‐0, TCLP‐0) and after ablation for 30 s (TCDP‐30, TCLP‐30). A quarter macro–meso hybrid model that takes into account the degradation of material properties after ablation and ablative crack pores was innovatively proposed. The predicted tensile elastic modulus is within 9% error from the experimental results. The results show that TCDP‐30 and TCLP‐30 have rapid damage expansion and lethal injury at smaller displacements than the pre‐ablation specimens. The displacement of the maximum load point of TCDP‐30 is 38.7% lower than that of TCLP‐30. The forms of damage in TCDP‐30 are dominated by matrix fragmentation and matrix cracks. The damage forms of TCLP‐30 are dominated by debonding and delamination. Highlights: Micro‐CT was used to collect matrix fabrication defects and ablative crack pores defect.A quarter macro–meso hybrid model that takes into account the degradation of material properties after ablation and ablative crack pore was innovatively proposed.The tensile failure mechanism of the material after ablation was revealed by the combination of experiment and numerical method. [ABSTRACT FROM AUTHOR]

Take the metamorphic sandstone as the reference object, by making rock like samples with fractures, the conventional triaxial loading and unloading test and PFC numerical simulation of rock like sample with single fracture were conducted, and the effects of the loading path, inclined angle of fracture, axial stress level during unloading, initial confining pressure during unloading on the compressive strength, peak strain and crack propagation evolution of the samples were considered. The compressive strength of the specimen under triaxial unloading is smaller than that under triaxial loading. The peak strain of the specimen under triaxial unloading is also smaller than that under triaxial loading. The specimen is more prone to brittle failure. When the axial stress level is the same during unloading, with the increase of the initial confining pressure during unloading, the difference of the compressive strength of the specimens with different inclined angles of fracture gradually decreases. Under the condition of uniaxial compression and triaxial compression, the failure of all specimens is tensile failure, and the shear failure is the main one during unloading. [ABSTRACT FROM AUTHOR]

Crack initiation and propagation in rocks exposed to injected fluids must be understood better for sustainable sequestration and geo-energy applications. One specific challenge is the characterization of the fluid-induced changes in the stress state and mechanical properties when multiple cracks grow and interact with each other. We conduct crack propagation tests on brine-exposed and supercritical CO 2 -exposed Indiana limestone samples under uniaxial compression conditions. By analyzing the displacement and strain fields using Digital Image Correlation and the first arrival time and amplitude of the transmitted shear waves, we characterize the effect of crack propagation and interaction events on stress and toughness. We build 3-D simulation models of crack propagation under uniaxial compression using the extended finite element method to analyze the 3-D stress and deformation fields in high resolution. We quantify the evolution of crack-tip's J-integral value with the crack length for wing cracks and shear cracks in samples exposed to mixtures of brine and supercritical CO 2 at subsurface conditions. Experimental and simulation results are synthesized to gain insights into crack propagation, shear-to-tensile failure transition, and interaction of cracks in fluid-exposed rocks. Crack length and J-integral analysis quantifies the impact of fluid exposure on the fracture toughness. [ABSTRACT FROM AUTHOR]

Composite materials consist of a matrix and fibers, and their failure modes differ significantly from those of isotropic materials. In undamaged composite materials, under increasing loads, matrix damage typically occurs first. At this stage, the damaged area experiences a stiffness reduction, redistributing stress until failure occurs elsewhere. As matrix damage progresses, debonding between fibers and the matrix begins, leading to delamination failure. With further load increase, the fibers eventually fracture. Finite element simulation with stiffness degradation methods can be employed to study composite material damage. This involves gradually degrading damaged elements, ultimately revealing the final failure mechanism of the composite material. Advances in finite element software now allow for precise engineering simulations, widely applied in the field. Consequently, this method can be used to simulate and analyze the failure of composite material flywheel rotors, identifying the factors contributing to their failure. This study uses progressive damage theory to simulate the failure process, establishing rational failure criteria for composite materials and utilizing a finite element stiffness degradation model. Greater interference fit results in higher compressive stress and initial stress, making the compressive stress and initial stress distribution of composite material flywheel rotors dependent on the interference fit. The study also analyzes the critical speeds of flywheels with single‐ring and multiring rotors under different interference fits, revealing the influence of interference fit on the maximum speed of the flywheel. [ABSTRACT FROM AUTHOR]

The mechanical behavior of fractured rock in tensile stress environment is a hot topic in underground mining engineering. Here, real surrounding rock of coal mine roadway was simulated by using rock-like materials and the tensile failure behavior of Brazilian discs with intermittent double fissures was investigated experimentally. The deformation response, fracture evolution, and failure mode of rock were analyzed. The fissured disc specimen's discrete element model was proposed in particle flow code (PFC2D). The microforce field, crack, and energy evolution processes of model specimens were discussed. The results showed that the load-displacement curves exhibit single-peak and double-peak types, corresponding to the splitting penetration and wing crack penetration damage modes of the specimen. The fissure angle or rock bridge angle showed a great influence on the evolution of main cracks and secondary cracks. The double-fissured Brazilian disc failed due to the initiation and transfer of microcracks in the stress concentration zone, combined with the continuous propagation and convergence of those microcracks. The splitting failure of the Brazilian disc is a continuous process of strain energy accumulation from the early stage of loading and instantaneous release of strain energy after obtaining the peak strength as the dissipative energy sharply rises. [ABSTRACT FROM AUTHOR]

Understanding the size dependence of quasi-brittle materials' fracture behavior is useful in assessing the safety of flawed rock engineering structures. In this study, a set of uniaxial compression tests were conducted to scrutinize the mechanical properties and crack morphology of cubic specimens with sizes of 75 mm, 100 mm, 125 mm and 150 mm. The results showed that the specimens had significant size dependence in terms of strength and crack initiation angle. The crack type and fracture pattern were not affected by the specimen size and were mainly controlled by the pre-existing crack inclination angle. Next, the test results were compared with the maximum tangential stress criterion considering the T-stress. The results also showed that the crack initiation angles of specimens with different sizes were in good agreement with the theoretical calculations. The non-singular compressive stress perpendicular to the crack surface inhibited the generation of the fracture process zone (FPZ). In addition, the stress required for tensile failure was smaller for large-size specimens, leading to a decrease in the length of the FPZ with increasing specimen size. The FPZ variation law of the uniaxial compression tests was greatly different from that of the mode I loading. [ABSTRACT FROM AUTHOR]

Quantifying the level of atomic disorder within materials is critical to understanding how evolving local structural environments dictate performance and durability. Here, we leverage graph neural networks to define a physically interpretable metric for local disorder, called SODAS. This metric encodes the diversity of the local atomic configurations as a continuous spectrum between the solid and liquid phases, quantified against a distribution of thermal perturbations. We apply this methodology to four prototypical examples with varying levels of disorder: (1) grain boundaries, (2) solid-liquid interfaces, (3) polycrystalline microstructures, and (4) tensile failure/fracture. We also compare SODAS to several commonly used methods. Using elemental aluminum as a case study, we show how our paradigm can track the spatio-temporal evolution of interfaces, incorporating a mathematically defined description of the spatial boundary between order and disorder. We further show how to extract physics-preserved gradients from our continuous disorder fields, which may be used to understand and predict materials performance and failure. Overall, our framework provides a simple and generalizable pathway to quantify the relationship between complex local atomic structure and coarse-grained materials phenomena. Level of atomic disorder in materials is critical to understanding the effect of local structure on materials properties. Here the authors present a workflow combining structure-aware graph neural networks and physics-inspired order parameter to characterize structural disorder on a per atom basis. [ABSTRACT FROM AUTHOR]

To study the anisotropic mechanical properties and energy evolution of layered rock masses under the action of cyclic loading, uniaxial graded cyclic loading and unloading tests under different upper and lower stress limits were carried out on samples with different bedding angles (0°, 22.5°, 45°, 67.5°, and 90°) to explore the deformation and mechanical response characteristics of bedded phyllite under cyclic loading and the mechanism controlling the evolution of the total absorption energy, elastic strain energy, and dissipated energy. The damage variable D and the damage increment ΔD were introduced to characterize the damage accumulation state inside the layered rock mass, and an instability criterion of bedded phyllite under mechanical cyclic loading was proposed. The results show that when the bedding angle increases from 0° to 90°, the failure types of the sample change from splitting shear failure to slipping shear failure and then to splitting tensile failure, and the corresponding irreversible strain and deformation modulus first decrease and then increase. With increasing stress level, the cumulative energy density increases in three stages, and the rate of increase presents a change in characteristic of "accelerating-steady-decelerating." The energy storage coefficient (Ke) decreases with increasing cycle number and stress level and first increases and then decreases with increasing bedding angle. Meanwhile, the energy dissipation coefficient (Kd) exhibits the opposite trend. The damage increment increases ΔD sharply after the first cycle in the nonfailure stage, drops sharply in the next cycle, and gradually decreases and stabilizes to near ΔD = 0.01 in the subsequent cycle. After entering the failure stage, the change in the damage increment of the variation in phyllite samples with different bedding angles is closely related to the stress level and number of cycles. The damage variable D can be used to describe the failure and instability of bedded phyllite under graded cyclic loading: when D ≤ 2 × 10–4, the rock is in the stage of compaction and steady crack growth; when D ≥ 2 × 10–4, the rock is at risk of failure and instability. Highlights: The changes in the irreversible strain and elastic modulus were analyzed based on the results of uniaxial graded cyclic loading and unloading testing. The evolution and distribution rules of various energy indicators under uniaxial graded cycle load are discussed from the perspective of energy. An instability judgment index based on energy dissipation theory is proposed, considering the relationship of layered millennium rock macro–micro deformation and energy evolution under the cyclic load. [ABSTRACT FROM AUTHOR]

Geofluids exist extensively in coal seams and affect greatly the mechanical behaviors of coal. To study the effect of water saturation pressure on the evolution of microcracking and ultimately the macrofailure, the mechanical behaviors and acoustic emission (AE) characteristics of coal treated at saturation pressures of 2–6 MPa were researched by performing uniaxial compression and direct tension tests. AE parameter analysis was utilized to identify cracking in the deformation stages of coal. The characteristics of AE parameters (AF and RA) during uniaxial compression and tension experiments were revealed. The results show that the average compression strength of coal sample decreases by 60.89% as the saturation pressure increases from 0 to 6 MPa. Moreover, the failure modes of coal change from mainly inclined plane shearing to tensile macrocracking. The mechanism of strength weakening and failure modes is that a higher saturation pressure (≥ 4 MPa) contributes to tensile microcracking more than shear microcracking in the unstable crack growth stage. As a consequence, tensile failure planes are the main macrofailure mode. In contrast, a lower saturation pressure (≤ 4 MPa) contributes to shear microcracking more than microcracking in the unstable crack growth stage, leading to inclined shear macrofailure. Therefore, the failure modes of coal can be predicted by the evolution of tensile and shear microcracking in the unstable crack growth stage. This study provides the basis for research on engineering issues such as underground coal pillar design in coal mines and the mechanisms of crack damage. [ABSTRACT FROM AUTHOR]

[Display omitted] • A clarification has been made on interfacial failure mechanism of the resistance spot welds under opening-mode loading. • Two primary failure mechanisms has been identified: ductile tensile failure and brittle crack propagation. • Two models were proposed to predict cross-tension interfacial strength based on structural stress and fracture mechanics. • The transition between the competing mechanisms is governed by ratio of fracture toughness to hardness of the fusion zone. • This clarification can help to design more sophisticated in-situ PWHT to improve weld mechanical properties. This paper addresses interfacial failure (IF) of automotive steel resistance spot welds under opening mode loading (i.e., Mode I), simulated through the cross-tension test. Two modeling approaches were developed to predict cross-tension strength (CTS) during IF: one based on structural stress and the other on fracture mechanics. The structural stress model correlates CTS with the hardness of the fusion zone, while the fracture mechanics model links CTS to the toughness of the fusion zone. Our evaluation of these models across various automotive steels reveals that the hardness-based model is suitable for steels with fusion zone hardness below 350 HV, where IF typically results in ductile fracture. In contrast, for higher-grade steels with fusion zone hardness exceeding 400 HV, the toughness-based model is more appropriate, as IF occurs through brittle crack propagation. The transition in the interfacial failure mechanism of spot welds under Mode I loading—from ductile tensile failure to brittle crack propagation—is governed by the ratio of toughness and hardness of the fusion zone. These insights not only refine the prediction of CTS but also inform the design of effective post-weld heat treatments aimed at enhancing CTS without sacrificing strength under shear loading mode, particularly through martensite refining strategy. [ABSTRACT FROM AUTHOR]

Understanding the brittle fracture behavior of rock is crucial for engineering and Earth science. In this paper, based on acoustic emission (AE) and laser Doppler vibration (LDV) monitoring technology, the staged damage behaviors of rock-like materials with different brittleness degrees under uniaxial compression are studied via multiple parameters. The results show that the brittleness degree determines the fracture mode. As the specimen's brittleness degree increases, the tensile failure increases and shear failure decreases. AE activity is enhanced at the crack damage point. With an increasing specimen brittleness degree, different instability precursor information is shown during the unstable crack growth stage: the AE b value changes from the fluctuating to continuously decreasing state, and the natural frequency changes from the stable fluctuation to upward fluctuation state. The AE b value near the stress drop is the smallest, and it decreases with an increasing brittleness degree. The natural frequency reduction indicates the rock-like fracture. The natural frequency is a symbolic index that reflects staged damage characteristics and predicts the amount of energy released by brittle failure. These findings provide guidelines for rock stability monitoring and provide support for better responses to stability evaluations of rock slopes, rock collapses, and tunnel surrounding rock in engineering. [ABSTRACT FROM AUTHOR]

The transverse cracking behavior of a carbon-fiber-reinforced plastic (CFRP) cross-ply laminate is investigated using a fatigue test and an entropy-based failure criterion in this study. The results of fatigue experiments show that the crack accumulation behavior depends on the cyclic number level and frequency, in which two obvious transverse cracks are observed after 104 cyclic loads and 37 transverse cracks occur after 105 cycles. The final numbers of transverse cracks decrease from 29 to 11 when the load frequency increases from 5 Hz to 10 Hz. An entropy-based failure criterion is proposed to predict the long-term lifetime of laminates under cyclic loadings. The transverse strength of 90° ply is approximated by the Weibull distribution for a realistic simulation. Progressive damage and transverse cracking behavior in CFRP ply can be reproduced due to entropy generation and strength degradation. The effects of stress level and load frequency on the transverse cracking behavior are investigated. It is discovered that, at the edge, the stress σ22 + σ33 that is a dominant factor for matrix tensile failure mode is greater than the interior at the first cycle load, and as stress levels rise, a transverse initial crack forms sooner. However, the initial transverse crack initiation is delayed as load frequencies increase. In addition, transverse crack density increases quickly after initial crack formation and then increases slowly with the number of load cycles. The proposed method's results agree well with those of the existing experimental method qualitatively. In addition, the proposed entropy-based failure criterion can account for the effect of load frequency on transverse crack growth rate, which cannot be addressed by the well-known Paris law. [ABSTRACT FROM AUTHOR]

This work is the continuation and completion to that initiated in the studies by Christensen (2022, "Perspective on the Bond Bending and Bond Stretching Effects of the Atomic Scale and Their Relationship to Ductile Versus Brittle Materials Failure," J. Mech. Phys. Solids, 167, p. 104984; 2023, "Review of the Basic Elastic Mechanical Properties and Their Realignment to Establish Ductile Versus Brittle Failure Behaviors," ASME Appl. Mech. Rev., 75(3), p. 031001) on the ductile/brittle transition for homogeneous and isotropic materials in uniaxial tensile failure. Starting here at the atomic level with the bonding involving both bond bending and bond stretching effects, there then is given the development of the ductile/brittle transition for a type of cubic symmetry in the individual crystals of the composing polycrystalline material. Thereafter, a complementary derivation is given for the ductile/brittle transition at the macroscopic level involving a specific form of the strain energy. The two results are found to be compatible and mutually verifying, thereby finishing the investigation. [ABSTRACT FROM AUTHOR]

In order to determine the effect of internal cracks on the tensile failure of materials, a hybrid finite–discrete element method was used to analyze the Brazilian disc test with cracks of different angles. When the pre-crack angle is between 0° and 60°, the wing crack is initiated from the pre-crack end. When the pre-crack is 90°, the crack initiated from the pre-crack center. When the pre-crack angle is between 0° and 60°, the maximum principal stress and plastic strain are concentrated at the pre-crack end. When the pre-crack angle is 90°, the maximum principal stress and plastic strain are concentrated in the pre-crack center. As the crack angle increased from 0° to 90°, the failure mode of Brazilian discs with cracks transits from splitting into two parts to splitting into four parts. The influence of crack length is further studied. When the crack length is less than 5 mm, the crack angle has little influence on the disc failure mode; Brazilian discs with cracks of different angles undergoes splitting failure along the loading axis. When the crack length is larger than 5 mm, the crack angle has a great effect on the disc failure mode. [ABSTRACT FROM AUTHOR]

To research the influence of different confining pressures on the damage evolution of defective sandstone, the sandstone numerical model with real mesostructure is established by RFPA3D using CT scan, and then carried out a triaxial compression test. The two-dimensional and three-dimensional mesoscale fracture box dimension algorithm using the digital image is compiled by MATLAB to quantitatively analyze the fractal characteristics. According to the research, as confining pressure increases, the stress corresponding to each characteristic point increases noticeably, and the specimen follows the law of transition from brittle to plastic failure under high confining pressure. The 0 MPa specimen is a tensile failure, the 5 MPa specimen is a tensile-shear mixed failure, and the 10 MPa and 15 MPa specimens are shear failures. Two types of fractal dimensions assess sandstone damage based on fracture development and fragmentation. The greater the fractal dimension, the more complete the fracture mode, and the greater the damage degree. Compared with other specimens, the mechanical characteristics and damage evolution of 0 MPa specimens are greatly different, and the fractal dimension is the largest. [ABSTRACT FROM AUTHOR]

Fluid loss during subterranean drilling often occurs through fractures that develop or preexist around the wellbore. Particulate additives, known as lost circulation material (LCM), are commonly added to the drilling fluid to mitigate lost circulation. The LCM forms an impermeable agglomerate within the fractures while preventing further tensile failure of the wellbore wall. The outcome is enhancement in the wellbore breakdown limit. A semi-analytical elastic solution is developed to estimate the width of near-wellbore fractures that partially close on the LCM agglomerate. The solution uses stress-strain data from confined compression testing on LCMs. The compression test results are modeled through a modified form of Kawakita's (1971) powder compaction equation. The developed constitutive model is embedded within the described semi-analytical solution for the wellbore fractures. The solution adopts an incremental loading approach to treat the nonlinearities arising from the characterized LCM constitutive behavior, as well as large deformation of the LCM agglomerate within the partially closed fractures. At each incremental load, the nonlocal stress equilibrium along the fracture length is described via an integral equation. Successive solutions to these integral equations determine the unknown fracture width of partially closed fractures. A competition between the fractures tendency for propagation and the wellbore wall tendency for secondary tensile failure determines the overall stability of the fractured wellbore. Mechanical behavior of the LCM agglomerate under compression is identified as a key parameter that controls both mechanisms, thereby, the gain in breakdown limit of a fractured and LCM-treated wellbore. [ABSTRACT FROM AUTHOR]

Complex branch cracks in practical engineering structures often have a great impact on structural damage, so the analysis of branch crack propagation is very important. The phase-field fracture model, a particular model for solving crack propagation without any ad hoc criteria, is very effective for complex crack propagation problems. In this research, several tensile experiments of 3D printed material containing designed complex cracks (Y-shaped and N-shaped) have been performed. The "i speed 716" high-speed camera is combined with a loading testing machine to capture the real-time whole fracture process in experiments. Based on the phase-field model, the influence of displacement increment and energy decomposition on the simulation results of crack growth is explored. Equilateral Y-shaped center crack specimens in different directions are designed to study the influence of crack angle on crack growth. The results show that the specimens' bearing capacity and propagation form with equilateral Y-shaped cracks change with the orientation of equilateral Y-shaped cracks under tensile load. When the orientation of the equilateral Y-shaped crack is 0° with the x-axis, the specimen is the most resistant to tensile force. When the orientation is 30°, the specimen is the most vulnerable to failure. In practical engineering, the occurrence of cracks at this orientation should be avoided as much as possible. Between 60° and 75°, the crack propagation form changes. The numerical simulations of the tensile failure of the 3D printed material with complex cracks agree with the experiments, and the errors of the maximum force on the failure are smaller than 7%. The model studied in this paper can predict the crack growth of 3D printed material with complex cracks from a qualitative and quantitative perspective. [ABSTRACT FROM AUTHOR]

• A novel numerical model for the damage and fracture behaviors of fiber-reinforced cementitious composites (FRCC) is introduced based on Peridynamic (PD) theory. • This Peridynamic fiber-reinforced Cementitious Composites (PD-FRCC) model improves the bond-based PD theory's capability to describe the intrinsic microstructural heterogeneity and macroscopic nonlinear mechanical properties of cementitious by introducing key damage correction factors. A semi-discrete method is used to simulate the reinforcement effect of fibers. • The effectiveness and stability of the proposed numerical model are validated by numerical simulation examples. These examples include tensile tests of single-fiber cementitious plates, static tensile tests of steel-polyethylene hybrid fiber reinforced engineered cementitious composites (ST/PE-ECC), and tensile failure simulations of double-notched beams. • The proposed numerical model accurately captures the complex morphology and propagation of FRCC cracks, and showcases high predictive accuracy. A novel numerical model for the damage and fracture behaviors of fiber-reinforced cementitious composites (FRCC) is introduced based on Peridynamic (PD) theory. This Peridynamic fiber-reinforced Cementitious Composites (PD-FRCC) model improves the bond-based PD theory's capability to describe the intrinsic microstructural heterogeneity and macroscopic nonlinear mechanical properties of cementitious by introducing key damage correction factors. A semi-discrete method is used to simulate the reinforcement effect of fibers, where a proportion of cementitious matrix bonds are randomly selected as fiber-reinforced bonds based on fiber content and length. The effectiveness and stability of the proposed numerical model are validated by numerical simulation examples. These examples include tensile tests of single-fiber cementitious plates, static tensile tests of steel-polyethylene hybrid fiber reinforced engineered cementitious composites (ST/PE-ECC), and tensile failure simulations of double-notched beams. The results demonstrate that the proposed numerical model accurately captures the complex morphology and propagation of FRCC cracks, and showcases high predictive accuracy. The significant impact of fiber bridging on material toughness and ductility during crack propagation is emphasized, revealing that fibers not only suppress initial crack growth but also lead crack propagation along complex paths, thereby extending crack propagation time and enhancing fracture resistance. [ABSTRACT FROM AUTHOR]

• A fiber Bragg grating method is proposed for monitoring type-I crack growth in rock. • Bandwidth expansion can indicate tensile failure of crack growth at various stages. • The change in peak reflectance is associated with unstable crack growth. • The monitoring effect of fiber Bragg grating and crack growth at 60° is optimal. The occurrence of rock mass engineering disasters can be reduced significantly by obtaining the key information in the process of rock internal fracture accumulation and evolution through advanced monitoring means and taking certain preventive measures. Through fiber Bragg grating monitoring tests of the type-I crack propagation in rock, the spectral characteristics of the fiber Bragg grating in the process of rock failure were analyzed, the bandwidth expansion was extracted to characterize the local tensile strain during the crack propagation process, and the damage variable based on the bandwidth expansion was calculated to describe the type-I crack propagation process. The research results showed the following: (1) The fiber Bragg grating generated a non-uniform local tensile strain during type-I crack propagation. The bandwidth expansion of the wave spectrum was positively correlated with the local tensile strain. The change in the characteristics of the wave spectrum could provide the local real strain in the process of crack propagation. (2) During the steady propagation of the type-I crack, the bandwidth increased obviously, while the number of acoustic emission events was relatively small, and most of them were in the process zone. The gentle increase in the bandwidth corresponded to the unstable growth stage of the type-I crack, which could be used as a precursor of rock sample instability. During loading, the maximum tensile strain of the type-I crack was 6 %, while the maximum shear strain reached 1.8 %, primarily attributed to tensile failure. The average value of fracture toughness K IC , based on the equivalent linear elastic fracture mechanics model, was determined to be 1.21 MPa·m1/2, and the average value of fracture energy G f was calculated as 57.7 N/m. The variation of peak reflectivity in fiber Bragg grating was associated with the closure of pre-existing defects and the propagation of microcracks in rocks, resulting in unstable shear strain at crack extension sites. (3) The damage variable D defined by the bandwidth broadening began to become concentrated and accumulated in the crack steady growth stage, and it increased slowly in the crack intensification and evolution stage. The grating was sensitive to changes when it was pasted to the surface at 90°, but it could easily fracture or become unable to capture spectral signals in time. Based on a comprehensive comparison, the monitoring effect was the best when the grating was pasted at 60° relative to the crack. [ABSTRACT FROM AUTHOR]

During deep shale gas production, flowing water-based working fluid inevitably cools shale reservoirs around boreholes and some fractures, and possible extraction methods induce dynamic stresses. To understand the dynamic tensile behavior of deep anisotropic shale reservoir after water-based working fluid cooling, a split Hopkinson pressure bar was used for performing the dynamic Brazilian tests on shale samples with bedding angles of 0°, 30°, 45°, 60° and 90° after reservoir temperature realization (25–200 °C) and water cooling. The results illustrate that dynamic tensile strength of shale samples decreases gradually as reservoir temperature increases under the loading rates 100–1000 GPa/s. From room temperature to 200 °C the most strength deterioration appears on samples with the bedding angle of 90°. A dynamic tensile strength deterioration model for deep shale reservoirs after water-based working fluid cooling is proposed considering the influence of loading rate and bedding angle. Geometrical trajectories of the main failure cracks are separated into three types, i.e., fully central tensile failure, tensile-shear failure and fully shear failure (sliding of bedding planes). For samples with bedding angles of 30°, 45° and 60°, increasing reservoir temperature encourages tensile failure to change into shear failure. The roles that bedding planes play in interacting with failure crack growth are summarized as IP mode (intersecting propagation), TP mode (turning propagation) and PP mode (promoting propagation). Anisotropic dynamic tensile strength responses are systematically discussed by using thermal stress simulation in ABAQUS, microstructure analyses, crack interaction conditions and the one-dimensional stress wave propagation theory. Based on experimental observations, field implications in borehole stability and fracturing of deep shale reservoirs are proposed under medium and high loading rates. This work is instrumental in providing valuable information and technology assistance for real deep shale gas production projects. [ABSTRACT FROM AUTHOR]

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Impact loading on carbon fiber reinforced polymer matrix (CFRP) composite laminates can result in a significant reduction in their residual properties, and the (ShAI) properties of the composite material are essential to obtain the material allowable values of the shear dominated composite structures. In order to obtain the ShAI properties of the composite material in pure shear stress at a coupon level, this study presents theoretical, experimental, and numerical methods and analysis work on the in-plane shear and ShAI properties of the composite laminates. Theoretically, a method of sizing the composite specimen loading in shear is developed through comparing the load values due to buckling and the material failure. Following this, both impact tests using the drop-weight method and ShAI tests using the picture frame test method are conducted, and the influences of the impact energies on the impact damage and the residual ShAI values are evaluated. Moreover, a progressive failure finite element model based on the Hashin's failure criterion and the cohesive zone model is developed, and a two-step dynamic analysis method is performed to simulate the failure process of the composite laminates under impact loading and ShAI loading. It is found that the impact damage with the cut-off energy, 50 J, causes a 26.8% reduction in the residual strength and the residual effective shear failure strain is about 0.0132. The primary reason of the shear failure is the propagation of both the matrix tensile failure and interlaminar delamination. It can be concluded that the proposed theoretical, experimental, and numerical methods are promising factors to study the ShAI properties of the composite materials. [ABSTRACT FROM AUTHOR]

This article substantiates a new approach to development of standards regarding assessment of metal crack resistance as exemplified by certain methods of metal identification in terms of operational reliability. It is proposed to substitute the index of classical impact toughness in quality certificate with two parameters: specific crushing energy and coefficient of dynamic viscosity, which are determined by calculations based on results of tensile failure tests of smooth specimens (State Standard GOST 1497–84, GOST 10006–80). [ABSTRACT FROM AUTHOR]

Background: Porosity and other defects resultant by additive manufacturing processes are well-known to affect mechanical properties. However, there remains limited understanding regarding how the internal defect structure influences the evolution of the local strain field, as experimental investigations have not presented direct measurements of the evolving internal strain field in the presence of defects. Objective: Interrupted in-situ tensile tests in a lab-based X-ray computed tomography machine were used to investigate the evolution of the strain field around internal defects. The evolution of the internal strain field facilitated examination of the role of specific defects in the macroscopic deformation of additively manufactured tensile coupons. Methods: Samples were produced in 316L stainless steel by laser powder bed fusion. An in situ loading device was utilized to subject the samples to tensile failure within a tomographic scanning environment. Digital volume correlation was utilized to directly determine local strain levels within the additively manufactured components in the vicinity of porosity defects. Results: Effects of porosity on strain localization and eventual failure of the samples were evaluated. Characteristics of the porosity distribution, including presence of porosity at the surface or near-surface of components, as well as the proximity of pores to each other were found to influence the evolution of failure. Early onset of failure was found to be associated with the availability of neighboring porosity that allowed for rapid progression of the fracture path. Conclusions: The direct measurements of strain field evolution in the present study established understanding regarding how internal defect structure characteristics influence the evolution of the local strain field for additively manufactured components. This high fidelity characterization and the associated phenomenological observations have bearing for supporting validation of numerical modeling frameworks for describing failure in these materials. [ABSTRACT FROM AUTHOR]

In order to study the effects of loading rates on the strength and failure of high-water-content material, the loading rates of 0.1, 0.5, 1, 2 and 5 mm/min were selected to conduct uniaxial tests on standard specimens with water cement ratios of 2:1, 4:1 and 6:1 by curing for 1, 3, 7 and 28 days, respectively. The mechanics and failure characteristics of high-water-content material in different loading rates and curing ages were obtained. The results show that the elastic modulus and peak strength of high-water-content material are in direct proportion to the loading rates and curing ages. However, the mass loss rate is inversely proportional to the loading rates and curing ages. When the loading rate is low, high-water-content materials mainly have a circumferential tensile failure. On the contrary, shear failure mainly occurs and more debris is produced. The effect mechanisms and the mutual feedback relationship between the loading rates and the mechanics and failure characteristics of high-water-content material are revealed. The results provide a reference for the selection of high-water-content material in the filling of underground coal mines. [ABSTRACT FROM AUTHOR]

Instability failure in rock mass engineering is closely related to expansion of joint fissures. In this study, uniaxial compression tests and acoustic emission (AE) measurements were carried out simultaneously on specimens of soft rock-like material with different fracture angles and connectivity values to better understand their influence on the deformation and failure of the material. The stress–strain curve and AE signal of fractured soft rock-like material are similar to those of intact soft rock-like; specifically, they exhibit a compaction, elastic deformation, stable fracture development, and unstable fracture development. The main differences between fractured and intact material occur during post-peak failure stage. Under the combined influence of fracture angle and connectivity, the uniaxial compressive strength of fractured soft rock-like material ( f cu ′ ) is lower than that of the intact soft rock-like material (fcu), and can be described by the relationship f cu ′ = f cu · α , where α is the strength reduction coefficient, fitted as α = 0.8228 + 0.00411 x - 0.00789 y . In this equation, x is the fracture angle ( ∘ ) and y is the fracture connectivity (%). Under uniaxial compression, the main types of secondary cracks were wing cracks and secondary coplanar cracks. The specimen with a fracture angle of 30° mainly underwent tensile failure under loading, whereas those with fracture angles of 45° and 60°mainly experienced shear failure under high-connectivity conditions (45%). [ABSTRACT FROM AUTHOR]

An effective biaxial tension and compression test method is proposed based on the shortcomings of current research for the mechanical properties of solid propellants under complex stress states. The equal proportion biaxial tension and compression test of HTPB (Hydroxyl-terminated polybutadiene) and NEPE (NitrateEster Plasticized Polyether) solid propellants is performed at different rates while at room temperature, and the damage morphology of the tension–compression zone is analyzed using micro-CT. The results show that the failure mode of the solid propellant under biaxial tension and compression loading is similar to that under uniaxial tension. Meanwhile, the compressive strength is much greater than the tensile strength, which will eventually cause tensile failure. With an increased loading rate, the growth trend of the initial modulus, ultimate strength, and maximum elongation of the propellant is gradually flattened, and the damage degree is gradually reduced. Additionally, damage that forms in the HTPB propellant is from dewetting and particle fracture while that for the NEPE propellant is from matrix tearing. The porosity can be used as the meso-damage parameter of the propellant. [ABSTRACT FROM AUTHOR]

A deformable spheropolygon-based discrete element method is developed to predict the evolution of fracture by coupling the finite element method (FEM) and the spheropolygon-based discrete element method (DEM). Within the framework of the coupling method, the spheropolygon-based DEM is adopted to capture the discontinuum behaviors, while the continuum behaviors are analyzed by the FEM. By introducing the fracture model of joint elements based on fracture mechanics, a continuous-discontinuous coupling approach for simulating the fracture of quasi-brittle materials is presented. The tensile failure is described with the fictitious crack model, meanwhile, the Mohr–Coulomb failure criterion with a tension cut-off is employed to determine the shear failure state. Finally, the results of numerical simulations indicate that this novel method is versatile in simulating the whole process of quasi-brittle materials from continuum to discontinuum, including the initiation and propagation of cracks, and the collision of fragments after the failure of brittle materials. [ABSTRACT FROM AUTHOR]

The existence of defects in a rock mass is a vital factor complicating the mechanical response of the rock mass under stress. The characteristics of defects control the rock mass's mechanical behaviors. This report reviews the experimental studies on the influence of simulating the internal defects of rock mass's mechanical properties. The effects of preexisting defects (shape, size, number, angle, and other factors) on the mechanical properties and failure modes of the rock are investigated from the perspectives of rock failure and fracture mechanics. The fracture propagation mechanisms of different defective rock masses are analyzed by studying the stress state of different defective rock masses under uniaxial compression. After the defective rock samples with varying inclination angles are destroyed, the relationship among the compressive strength, the fracture propagation, and the failure characteristics is explored. The primary findings are as follows. The increase in the size and number of defects rapidly damages the mechanical properties of the rock and intensifies defect penetration and expansion. The rock mechanics characteristics of fissured rocks with different inclination angles show two primary variations: one is a continuous increase, and the other is a decrease followed by an increase. This result is strongly related to the failure pattern of rocks with preexisting fissures. This investigation is crucial for further studying the failure modes of complex defective rock masses and the geotechnical engineering related to defective rocks. [ABSTRACT FROM AUTHOR]

• Both experimental and numerical investigations are conducted. • Four crushing regions and corresponding damage patterns are identified. • Groove-assisted impact rock-breaking mechanism is revealed. • Increasing the head number is not conducive to increasing penetration depth. • Shear damage causes small rock chips, while tensile damage generates large fragments. Groove-assisted impact rock-breaking represents a critical mechanical method for fracturing rocks; however, comprehending its underlying mechanisms governing fracture initiation and propagation remains incomplete. This paper aims to fill this knowledge gap by first establishing a dedicated test bench for groove-assisted impact rock-breaking and conducting double-impact head experiments with varying spacings. Subsequently, a finite discrete element method (FDEM) model is developed, incorporating zero-thickness cohesive elements, to validate and refine the numerical simulations against experimental outcomes. The investigation then systematically explores the impacts of double-head and multi-head rock-breaking to elucidate the dynamic evolution of stress fields and damage processes throughout the rock-breaking sequence. This includes the formation of dense cores, the initiation and propagation of fractures, and the eventual propagation of splitting damage. Noteworthy findings of this study include the identification and characterization of four distinct damage zones: an intermediate impact breakage zone dominated by shear damage, an annular extrusion damage zone typified by tensile failure, a primary surface cracking damage zone, and an interconnecting damage zone between dual impact heads, both characterized by tensile damage. Additionally, the study examines variations in penetration depth relative to the number and positioning of impact heads under conditions of equal energy input. These insights significantly enhance our understanding of the fracture mechanics involved in groove-assisted impact rock-breaking and lay the groundwork for enhancing rock-breaking efficiency. [ABSTRACT FROM AUTHOR]

• The effects of bedding inclination and hole on the failure mode and AE characteristics of shale were studied. • The failure mode and acoustic emission characteristics of the shale samples are significantly anisotropic. • The stress concentration induced by the hole changes the failure mode and the acoustic emission characteristics of the shale samples. • The acoustic emission signals are effective in identifying the type of cracks in the sample during the failure process. • The number of acoustic emission signals generated from tensile cracks and shear cracks differs for different loading stages. Shale is a kind of layered sedimentary rock widely existing in nature. In slope engineering, tunnel engineering, shale gas engineering and other practical engineering, layer structure and orientation will lead to the structural strength reduction, easy to cause safety accidents. In this study, the acoustic emission (AE) characteristics and fracture modes of shale samples containing a circular hole were investigated by uniaxial compression tests with different bedding angles. The experimental results revealed that the fracture modes of the sample are affected not only by the dip angle of bedding, but also by the stress concentration caused by the hole. Different fracture modes lead to differences in AE characteristics such as ring number, b- value, energy and peak frequency. Compared with shear failure, the cumulative AE count and peak frequency of tensile failure are higher, and the change frequency of the b- value is higher. Additionally, according to the RA-AF distribution characteristics of the shale samples, AF = 10RA + 21 was confirmed as the dividing line of different crack types, and the dividing result was consistent with that of macroscopic cracks. According to this dividing line, the crack evolution process was analyzed, and it was found that the tensile cracks and shear cracks were concentrated in the peak stress and phase of crack steady growth respectively. The study of AE characteristics of shale will provide experimental basis and reference for guiding related engineering practice. [ABSTRACT FROM AUTHOR]

• FMC is used for translaminar fracture toughness characterisation. • Glass fibre/PA6 laminated composites by varying the thickness are considered. • The experimental campaign is numerically simulated. • Considerations on fracture toughness dependence on specimen sizes are provided. This paper proposes a novel approach for the characterisation of the material fracture toughness associated with translaminar tensile failure, consisting in the application of the Fictitious Material Concept (FMC) by using the testing configuration of the Modified Two Parameter Model (MTPM). The main advantage of such an approach is to avoid the use of nonlinear fracture mechanics for material fracture toughness characterisation. The novel approach is applied to compute the translaminar fracture toughness of a unidirectional glass fibre (GF)/polyamide 6 (PA6) laminated composite. Moreover, the experimental campaign carried out is numerically simulated by means of a micromechanical finite element model, and the fracture toughness is computed by employing two different approaches, that is, the novel one and the MTPM. The present study proves, for the first time, that the Fictitious Material Concept can be applied by considering both experimental and numerical structural responses since it provides, in both cases, quite satisfactory accuracy in term of laminated composite fracture toughness. Therefore, the great advantage is that, when a validated numerical model is available, experimental campaigns may be avoided, saving time and money. Moreover, it is proved that the FMC can be used to investigate specimen size effect on fracture toughness. [ABSTRACT FROM AUTHOR]

The interface and porosity play important roles in determining the damage of C/C composites (C/Cs). This study presents a novel finite element model that incorporates cohesive elements with porosity. Based on this model, numerical analyses were conducted to investigate the axial compressive damage of C/C composites with orthogonal woven structure (3DOW) and fine weave pieced (3DFWP) structures, both of which are 3D woven structures. The results indicate that damage initially occurs at the interface, and axial fiber damage is the decisive factor in material failure. The pores at the interface have little effect on the failure of C/Cs. Eliminating the pores within the fibers significantly improves the compression performance of the material, and the strengths of the two structural models increase by 28% and 6%. [ABSTRACT FROM AUTHOR]

A novel hot-melt cyclic olefin-based adhesive was designed as a transparent, non-tacky film of amorphous thermoplastic with a unique polymer micro-structure. The aim of the present paper is to assess the mechanical properties of the 0.1 mm thick COP hot-melt adhesive film through adhesive characterizations tests. The glass transition temperature was determined using dynamic mechanical analysis (DMA). For mechanical characterization, bulk and thick adherend shear specimens were manufactured and tested at a quasi-static rate, where at least three specimens were used to calculate the average and standard deviation values. Tensile tests revealed the effects of molecular chain drawing and reorientation before the onset of strain hardening. Thick adherend shear specimens were used to retrieve shear properties. Fracture behaviour was assessed with the double cantilever beam (DCB) test and end-notched flexure (ENF) test, for characterization under modes I and II, respectively. To study the in-joint behaviour, single lap joints (SLJs) of aluminium and carbon fibre-reinforced polymer (CFRP) were manufactured and tested under different temperatures. Results showed a progressive interfacial failure following adhesive plasticization, allowing deformation prior to failure at 8 MPa. An adhesive failure mode was confirmed through scanning electron microscopy (SEM) analysis of aluminium SLJ. The adhesive exhibits tensile properties comparable to existing adhesives, while demonstrating enhanced lap shear strength and a distinctive failure mechanism. These characteristics suggest potential advantages in applications involving heat and pressure across automotive, electronics and structural bonding sectors. [ABSTRACT FROM AUTHOR]

This study aims to investigate the mechanical properties and energy characteristics of coal-rock combinations during uniaxial compression, specifically focusing on variations in interface inclination angles. Each of the stress–strain curves of the CRC (Coal-Rock-Like Material Combination) with varying interface inclination angles were obtained using the DYD-10 universal testing machine and a high-definition camera system. Subsequently, the energy of the CRC was calculated using a specific formula. The experimental results demonstrated that when the interface inclination angles increased, the compressive strength and elastic modulus of the CRC showed a monotonous decreasing trend. The storage of elastic energy mainly occurred in the elastic stage and the plastic fracture stage, and the growth of dissipated energy increases obviously in the post-peak failure stage. As the inclination angles of the interface experience a rise, the energy storage limit (ESL) of the specimen decreases obviously, the CRC was more prone to fracture as the rate of dissipated energy conversion gradually increased. In order to understand the process of coal and rock mass disasters and prevent coal and gas outbursts, the mechanical features and fracture energy characteristics of the CRC under various interface dip angles were examined in this article. [ABSTRACT FROM AUTHOR]