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Fractures in body-centered-cubic metals and alloys below the ductile-to-brittle transition temperature are brittle. This is theoretically explained by the notion that the critical stress intensity factor of a given crack front for brittle fracture is smaller than that for plastic deformation; hence, brittle fracture is selected over plastic deformation. Although this view is true from a macroscopic perspective, such a fracture is always accompanied by small-scale plastic deformation near the crack tip, that is, crack tip plasticity. This paper investigates the origin of this plasticity using atomistic modeling with the machine learning interatomic potential of α -Fe. Some plastic modes are activated by rapid crack propagation, whereas no plasticity is activated when the crack tips are gradually fractured. The group of activated atoms dynamically caused by brittle crack propagation was identified as the precursor of plasticity. [ABSTRACT FROM AUTHOR]

Amorphous intergranular films (AIFs) have been proven in experiments to improve the damage tolerance of nanocrystalline materials. However, a quantitative study is still lacking. Molecular dynamics simulations were performed here to investigate the effect of CuNb AIFs on the fracture toughness of nanocrystalline Nb. In order to clarify the role of AIFs, a bicrystal Nb model with one straight symmetrical tilt grain boundary and a mode-I crack in one of the grains was constructed, in which the AIF effect was introduced by replacing the normal grain boundary with a CuNb AIF. Then, AIF thickness-dependent tensile deformation of the bicrystal Nb samples was simulated. The work-of-fracture, which is defined as the released strain energy due to the newly generated unit area in the crack during stretching, was employed to quantify the fracture toughness of the bicrystal systems. The results show that the fracture toughness of the AIF sample can be tripled due to the blunted crack tip and the relieved stress concentration at the crack tip as compared to the AIF-free one that exhibits a brittle crack propagation behavior. Also, the thicker the AIFs, the more pronounced this reinforcing effect. More importantly, it is found that there exists a critical AIF width of 1.7 nm, below which the crack will eventually break through the AIF, and above which the crack failed to do this. It is revealed that the enhanced fracture toughness originated from the transformation of brittle crack propagation to abundant dislocation emission from AIFs. [ABSTRACT FROM AUTHOR]

We discuss the origin of the breakloose (or static) friction force when an ice block is slid on a hard randomly rough substrate surface. If the substrate has roughness with small enough amplitude (of order a 1 nm or less), the breakloose force may be due to interfacial slip and is determined by the elastic energy per unit area, Uel/A0, stored at the interface after the block has been displaced a short distance from its original position. The theory assumes complete contact between the solids at the interface and that there is no elastic deformation energy at the interface in the original state before the application of the tangential force. The breakloose force depends on the surface roughness power spectrum of the substrate and is found to be in good agreement with experimental observations. We show that as the temperature decreases, there is a transition from interfacial sliding (mode II crack propagation, where the crack propagation energy GII = Uel/A0) to opening crack propagation (mode I crack propagation with GI the energy per unit area to break the ice–substrate bonds in the normal direction). [ABSTRACT FROM AUTHOR]

An extended ordinary state-based peridynamic model was developed to investigate the crack propagation of surrounding rock due to tunnel excavation. The frost heave effect on the crack surface was described by an equivalent pressure density. Two numerical examples were conducted to verify the effectiveness and robustness of the proposed model. Moreover, the influence of frost heave pressure, buried depth and rock elastic modulus on damage characteristics of the surrounding rock was investigated. The results demonstrate that massive microcrack damage will be formed at the invert when the tunnel is excavated in a deeply buried rock mass or soft rock stratum. A peridynamic model of rock mass under excavation and frost heave was constructed. Damage characteristics of surrounding rock could be simulated efficiently. Frost heave load was exerted on the crack surface by an equivalent pressure density. The effects of frost heave load, buried depth and rock elastic modulus were studied. [ABSTRACT FROM AUTHOR]

To adapt to the different application environments, Si 3 N 4 ceramics are required to have different mechanical properties. Therefore, in this study, Si 3 N 4 ceramics with adjustable mechanical properties were fabricated via using ZrN–AlN–Y 2 O 3 ternary sintering additives and hot-pressing at 1650 °C for 30 min. Subsequently, the effect of the Y 2 O 3 concentration on the phase assemblage, microstructure, mechanical properties, and crack propagation of Si 3 N 4 ceramics was systematically investigated. The results demonstrated that Si 3 N 4 ceramics presented adjustable microstructure and mechanical properties with the Y 2 O 3 contents added in the range of 0∼8 wt%. With the increase of Y 2 O 3 contents, the average aspect ratio of Si 3 N 4 grains had an increase of 61.77%, increasing from 3.95 to 6.39. Besides, the Si 3 N 4 grains and the formed YAG intergranular phase exhibited a fairly good combination at the nano-scale. Si 3 N 4 grains and intergranular phase were the main influence factors on the mechanical properties of Si 3 N 4 ceramics. As a result, the bending strength was from 700.99 ± 38.72 to 961.13 ± 36.84 MPa. The fracture toughness exhibited a range of 4.87 ± 0.11 to 6.10 ± 0.23 MPa⋅m1/2, while Vickers hardness achieved a high level of 16.09 ± 0.16 to 19.98 ± 0.39 GPa. [ABSTRACT FROM AUTHOR]

Continuous Al 2 O 3 fiber-reinforced Al 2 O 3 matrix (Al 2 O 3 /Al 2 O 3) composites, aimed at aerospace applications, are recognized for their low density, high strength, and resistance to oxidation but suffer from limited toughness. To address this problem, a study was undertaken that utilized a slurry infiltration and sintering (SIS) process for the fabrication of Al 2 O 3 /Al 2 O 3 composites with enhanced toughness. Composites have a microstructure that fine Al 2 O 3 matrix filled the voids of coarse Al 2 O 3 matrix, enhancing the tortuosity of crack propagation paths and thereby increasing the toughness of the composites. Additionally, the incorporation of LaPO 4 coatings was explored as a means to further augment toughness. Findings indicate that the optimal Al 2 O 3 /Al 2 O 3 composites, exhibiting superior performance, were fabricated at 1200 °C, achieving a density of 2.97 g/cm3, flexural strength of 209 ± 20 MPa, and fracture toughness of 13 ± 3 MPa m1/2. A 320 nm LaPO 4 coating was found to enhance the fracture toughness of the composites by approximately 20.70 %. Consequently, the SIS technique, complemented by the application of LaPO 4 coatings, represents a highly effective approach for the production of Al 2 O 3 /Al 2 O 3 composites with significantly improved toughness. [ABSTRACT FROM AUTHOR]

When dealing with badly preserved cadavers or skeletal human remains, the assessment of death circumstances remains challenging. When forensic evidence cannot be taken from the skin and soft tissue, the information may only be deduced from more resistant elements such as bone. Compared to cranial gunshot injuries, reliable data on ballistic long bone trauma remains scarce. This study aims to define ballistic fracture characteristics in human long bones. The shaft of 16 femurs and 13 humeri from body donors was perpendicularly shot with a 9-mm Luger full metal jacket bullet at an impact velocity of 360 m/s from a distance of 2 m. Some bones were embedded in Clear Ballistics Gel®, and some were shot without soft tissue simulant in order to better visualise the fracture propagation on the high-speed camera. The fractures were examined macroscopically and compared between the sample groups. We consistently found comminuted fractures with a stellate pattern. Fracture details were classified into entrance, exit and general characteristics. For some traits, we detected different occurrence values in the group comparison. The results indicate that some of the traits depend on bone properties such as shaft diameter, bone length and cortical thickness. The presence of ballistic gel also influenced some fracture traits, emphasising the relevance of soft tissue simulant in osseous gunshot experiments. This study revealed new insights in the detailed fracture pattern of human long bones. These may serve as guidelines for the identification and reconstruction of gunshot trauma in human long bones. [ABSTRACT FROM AUTHOR]

A snow slab avalanche releases after failure initiation and crack propagation in a highly porous weak snow layer buried below a cohesive slab. While our knowledge of crack propagation during avalanche formation has greatly improved over the last decades, it still remains unclear how snow mechanical properties affect the dynamics of crack propagation. This is partly due to a lack of non-invasive measurement methods to investigate the micro-mechanical aspects of the process. Using a DEM model, we therefore analyzed the influence of snow cover properties on the dynamics of crack propagation in weak snowpack layers. By focusing on the steady-state crack speed, our results showed two distinct fracture process regimes that depend on slope angle, leading to very different crack propagation speeds. For long experiments on level terrain, weak layer fracture is mainly driven by compressive stresses. Steady-state crack speed mainly depends on slab and weak layer elastic moduli as well as weak layer strength. We suggest a semi-empirical model to predict crack speed, which can be up to 0.6 times the slab shear wave speed. For long experiments on steep slopes, a supershear regime appeared, where the crack propagation speed reached approximately 1.6 times the slab shear wave speed. A detailed micro-mechanical analysis of stresses revealed a fracture principally driven by shear. Overall, our findings provide new insight into the micro-mechanics of dynamic crack propagation in snow, and how these are linked to snow cover properties. [ABSTRACT FROM AUTHOR]

Purpose: An investigation was conducted into the impact of various process parameters on the surface and subsurface quality of glass-ceramic materials, as well as the mechanism of material removal and crack formation, through the use of ultrasonic-assisted grinding. Design/methodology/approach: A mathematical model of crack propagation in ultrasonic-assisted grinding was established, and the mechanism of crack formation was described through the model. A series of simulations and experiments were conducted to investigate the impact of process parameters on crack depth, surface roughness, and surface topography during ultrasonic-assisted surface and axial grinding. Additionally, the mechanism of crack formation was explored. Findings: During ultrasonic-assisted grinding, the average grinding forces are between 0.4–1.0 N, which is much smaller than that of ordinary grinding (1.0–3.5 N). In surface grinding, the maximum surface stresses between the workpiece and the tool gradually decrease with the tool speed. The surface stresses of the workpiece increase with the grinding depth, and the depth of subsurface cracks increases with the grinding depth. With the increase of the axial grinding speed, the subsurface damage depth increases. The roughness increases from 0.780um/1.433um. Originality/value: A mathematical model of crack propagation in ultrasonic-assisted grinding was established, and the mechanism of crack formation was described through the model. The deformation involved in the grinding process is large, and the FEM-SPH modeling method is used to solve the problem that the results of the traditional finite element method are not convergent and the calculation efficiency is low. [ABSTRACT FROM AUTHOR]

Delayed hydride cracking (DHC) is a hydrogen embrittlement phenomenon that may potentially occur in Zircaloy-4 fuel claddings during dry storage conditions. An experimental procedure has been developed to measure the toughness of this material in the presence of DHC by allowing crack propagation through the thickness of a fuel cladding. Notched C-ring specimens, charged with 100 wppm of hydrogen, were used and pre-cracked by brittle fracture of a hydrided zone at the notch root at room temperature. The length of the pre-crack was measured on the fracture surface or cross-sections. Additionally, a finite element model was developed to determine the stress intensity factor as a function of the crack length for a given loading. Two types of tests were conducted independently to determine the fracture toughness with and without DHC, K I DHC and K I C , respectively: (i) constant load tests at 150 ∘ C, 200 ∘ C, and 250 ∘ C; (ii) monotonic tests at 25 ∘ C, 200 ∘ C, and 250 ∘ C. The results indicate the following: (1) there is no temperature influence on the DHC toughness of Zircaloy-4 between 150 and 250 ∘ C ( K I DHC ∈ 7.2 ; 9.2 MPa m ), (2) within this temperature range, the fracture toughness of Zircaloy-4 is halved by DHC ( K I C ∈ 16.9 ; 19.7 MPa m ), (3) the crack propagation rate decreases with decreasing temperature and (4) the time before crack propagation increases as the temperature and loading decrease. [ABSTRACT FROM AUTHOR]

This work reports a selective median crack propagation phenomenon in glass, leading to a novel glass cutting process. We found that by scribing a glass sample to the extent of plastic deformation with a deformation depth of 100–400 nm, followed by inducing an initial crack, a subsurface crack with a depth of ~ 10 μm was propagated backward along the centerline of the scribed region with a speed of 1 μm/s order. The crack depth and propagation speed were increased by increasing the scribing load. We conclude that the propagation direction was determined by the effect of the shear stress caused by a scribing tip sliding motion. [ABSTRACT FROM AUTHOR]

To achieve low-cost preparation of high-performance high-entropy oxide, ZrO 2 (3Y)-reinforced (MgCoNiCuZn)O matrix composite ((MgCoNiCuZn)O–ZrO 2 (3Y)) was prepared in a few seconds by ultrafast high-temperature sintering (UHS) technology in this work. Microstructure, phase composition, crystal structure, and mechanical properties of the (MgCoNiCuZn)O–ZrO 2 (3Y) composite were investigated systematically. The results indicated that, after UHS sintering with applied current of 22 A for 2 min, the enhancement of ZrO 2 (3Y) were well dispersed in the (MgCoNiCuZn)O matrix. The microhardness and fracture toughness of the UHSed (MgCoNiCuZn)O–ZrO 2 (3Y) were 6.43 GPa and 2.27 MPa·m0.5, which were much higher than those of the traditional sintered (MgCoNiCuZn)O–ZrO 2 (3Y) (1.65 GPa and 0.98 MPa·m0.5) and UHSed (MgCoNiCuZn)O without ZrO 2 (3Y) (4.06 GPa and 1.42 MPa·m0.5). The toughening mechanism of the UHSed (MgCoNiCuZn)O–ZrO 2 (3Y) was discussed in detail based on the microstructural feature and crack propagation behavior. In summary, this study provided insight into the advantages of incorporating ZrO 2 (3Y) and UHS technology to reinforce high-entropy oxides. [Display omitted] • Refined high-entropy composite (MgCoNiCuZn)O–ZrO 2 (3Y) was prepared using UHS method. • The microhardness and fracture toughness were increased by 58.37% and 59.86%. • The toughening mechanism mainly includes dispersion, phase transformation toughening. [ABSTRACT FROM AUTHOR]

This paper contains the solution to the problem of a semi-infinite moving crack situated in an orthotropic strip bonded between two identical strips. The crack moves with a constant velocity, and the surface is under shear wave disturbance. We first examine the equations of elasticity, which include equilibrium equations and stress and displacement constitutive relations with the model-specific continuity and boundary conditions. Using the Fourier integral transform, the standard form for the Wiener–Hopf (W-H) equation is obtained, which is solved using the W-H method. The analytical expressions for the considered crack problem have been obtained for stress intensity factor (SIF), normalized stress intensity factor (NSIF), and stress magnification factor (SMF). The behavior of NSIF has been graphically presented for particular cases of composite materials for different crack propagation velocities and various depth ratios of the strips. The novelty of this paper lies in the analytic solutions using the W-H method for the semi-infinite moving crack problem under the influence of anti-plane shear waves. The pictorial presentations of normalized SIF clearly show their dependency on strip depths, crack propagation velocities and elastic constants. [ABSTRACT FROM AUTHOR]

Cluster spacing optimization in non-uniform stress field, with the optimal stimulated reservoir volume (SRV) as target, which is critical for deep shale gas fracturing performance. A non-uniform stress field characterization model and a fracture network propagation model were constructed. The diagrams of the optimal cluster spacing were drawn based on the fault development in the Y1-01 well area. The results showed that the horizontal well should be deployed at a distance of between 2,000 and 4,000 m from the first-level fault, 1,500 and 2,500 m from the second-level fault, 700 and 1,200 m from the third-level fault, and an acceptable distance from the fourth-level fault. The shorter the distance to the fault for first-level faults, the bigger difference in horizontal stress, which was not conducive for fracture network propagation, and the smaller the optimal cluster spacing. For second-level, third-level, and fourth-level faults, when the fault strike was less than 50°, the closer to the fault, the bigger the difference in horizontal stress and the smaller the optimal cluster spacing. When the fault strike was greater than 50°, the farther away from the fault, the bigger the difference in horizontal stress, and the smaller the optimal cluster spacing. [ABSTRACT FROM AUTHOR]

Colored asphalt mixtures have recently found extensive applications in roads and public spaces due to their contribution to traffic management as well as aesthetics and landscaping. The development of durable colored asphalts using various materials has been a hot research topic in recent years. Colored asphalt can be developed through the durable colored slurry seal mixture (CSSM) technology. The desired quality of CSSM requires particular attention to the mechanical performance and resistance against crack propagation due to temperature variations and traffic loads. This research aimed at investigating the effect of steel slag (SS) aggregate compared with natural aggregate (NA) on the fracture behavior and performance of CSSM in five different mixtures: NA100% (control sample), SS10%+NA90% , SS20%+NA80% , SS30%+NA70% , and SS40%+NA60%. The performance of CSSM was evaluated using an edge-notched disk bend (ENDB) specimen fracture test at three different temperatures (0°C, −10°C , and −20°C). Additionally, cohesion test, wet track abrasion test, loaded wheel test (LWT)-displacement and LWT-sand adhesion were carried out to further examine the samples. Comparison of the fracture behavior of colored mixtures revealed that the SS40%+NA60% mixture outperformed other mixtures. The results of other performance tests showed that the unique characteristics of SS40%+NA60% mixture improved CSSM performance against vertical displacements, bleeding, cohesion, and moisture sensitivity by approximately 40.2%, 4 7.3%, 28.6%, and 52.7%, respectively. This comprehensive assessment offers valuable insights into the effectiveness of SS as a proper alternative to NA in CSSMs. [ABSTRACT FROM AUTHOR]

Biomedical magnesium (Mg) alloys remain a challenge for their mainstream application, because the combination of bio‐mechanical stress and corrosive physiological environment leading to stress corrosion cracking (SCC). It is crucial to avoid the sudden brittle fracture of Mg alloys in vivo for predicting their service duration. However, the key factors, such as surface or physiological environment features, determining the origination or propagation of SCC behavior are still unclear. In the present study, a prefabricated surface defects coating was prepared by the phytic acid (PA, C6H18O24P6) conversion treatment. Four mimicking physiological media were used, ranging from simple to equivalent (Dulbecco's Modified Eagle Medium and Protein [DMEM+Pro]). The results showed that the PA film with numerous micro‐cracks provided limited protective ability in synthetic biological media. A striking finding was determined that although initial high corrosion rate of samples in DMEM+Pro led to an increased SCC nucleation, significant ductile fracture with elongation to failure (14.86%) was observed. Combined with the fracture features, the adsorption or deposition of biological composition into the tunnel of SCC cracks significantly inhibited the hydrogen embrittlement (HE) behavior. These results indicate that preventing the propagation of SCC crack by biological composition, rather than nucleation, plays a key role in avoiding the sudden fracture of Mg alloys. It provides a novel perspective to determine the non‐brittle fracture of Mg alloys for biomedical applications. Highlights: Prefabricated surface‐defective Mg novelty used to study stress corrosion crackingConfirming ductile fracture of Mg alloy in vitro organic‐containing mimic mediumInhibiting the micro‐crack propagation relied on biological composition depositionThe crack propagation than nucleation plays a key role in avoiding brittleness [ABSTRACT FROM AUTHOR]

Rolling can result in anisotropy in the microstructure and mechanical properties of the sheet material. This study focuses on the very high cycle fatigue (VHCF) performance of magnesium alloys in the rolling direction (RD), normal direction (ND), and the bisecting angle between the ND and RD (ND–RD). The findings reveal that RD specimens demonstrate superior fatigue performance, while the ND specimens exhibit the lowest fatigue resistance. During the crack initiation stage, the primary influential factor is the maximum shear stress. Due to c‐axis alignment with ND direction in grains, the deformation mode for ND and RD specimens primarily involves first‐order pyramidal slip, while ND–RD specimens primarily undergo basal slip and prismatic slip. In early stable crack propagation, grain size and texture cause variations in the morphology of the rough area among the three directional specimens. Notably, the RD specimens show faster crack propagation during crack initiation than early stable propagation stage. Highlights: The rolled Mg alloys have the highest very high cycle fatigue strength along rolling direction.Texture and grain boundaries significantly affect crack initiation and early propagation.Maximum shear stress dominates slip‐induced crack initiation within primary grains. [ABSTRACT FROM AUTHOR]

Si3N4 ceramics with high mechanical properties and thermal conductivity, exhibiting fine and bimodal microstructure, were prepared by adjusting the Er2O3/MgO ratio and hot‐pressing sintering at 1800°C for 4 h. The microstructure, grain distribution, lattice oxygen content, mechanical properties, and crack propagation process of the sintered bulk samples were systematically investigated. It was found that a low Er2O3/MgO ratio contributed to the densification of Si3N4 ceramics, whereas a high Er2O3/MgO ratio favored the grain growth of Si3N4 ceramics. In this research, the grain size distribution and average diameters as well as their impact on mechanical properties were examined. When the ratio of Er2O3/MgO was 3:1, Si3N4 had a larger average diameter and higher thermal conductivity, but the mechanical properties were somewhat reduced. When the ratio of Er2O3/MgO was 2:2, the sample displayed enhanced mechanical performance, which can be explained by the formation of a bimodal structure. The research indicates that it is feasible to control the microstructure and optimize the mechanical properties of Si3N4 ceramics by tailoring the sintering additives. [ABSTRACT FROM AUTHOR]

The high cost of ReB2 limits its application as a member of novel high‐hardness materials, which can be alleviated by forming composites with cheap compound(s). In the present study, a dense ReB2–B4C composite was fabricated via in situ reactive sintering by spark plasma sintering with Re and B13C2 (Re:B = 1:20) as raw materials. The phase composition, microstructure, Vickers hardness, and fracture toughness of the obtained composite were characterized, and the reaction mechanism, crack propagation, and toughening mechanism were clarified. XRD, SEM, Raman, and XPS results revealed that the obtained composite is mainly composed of ReB2 and B4C phases, with a small amount of free B and graphite coexisted. Vickers hardness of 33.5 ± 4.4 GPa under 0.49 N load and 24.6 ± 1.5 GPa under 4.9 N load and fracture toughness of 5.02 ± 0.37 MPa·m1/2 were observed for the obtained composite. The toughening mechanism of the obtained ReB2–B4C composite including crack deflection crack and cracking bridging was analyzed in detail. [ABSTRACT FROM AUTHOR]

To investigate the effects of thermal treatment and loading conditions on the crack initiation and propagation characteristics of quartz‐diorite, mixed mode I + II fracture tests were conducted by using three‐point bending (TPB) specimens. The numerical model, established on ABAQUS, couples the initial fracture toughness criterion and cohesive zone model to predict the crack initiation and propagation. The effects of thermal treatment and loading conditions on the crack propagation process, crack resistance curve, fracture path, and some fracture parameters at peak load have been analyzed and discussed. The results demonstrate that the thermal treatment has an obvious influence on the crack resistance curve of the specimen. The crack of the specimen will be dominated by the mode I fracture component with crack extension. The numerical results also show that the temperature and loading condition affect the crack length and fracture toughness at peak load. [ABSTRACT FROM AUTHOR]

This paper discusses the effect of reversed austenite (RA) on hydrogen embrittlement (HE) behavior of a high-strength multi-alloyed steel. Three heat treated samples were fabricated by quenching-lamellarization-tempering (QLT) treatment with varying the features of RA. The experimental results revealed that the existence of reversed austenite could reduce the effective diffusion coefficient and HE susceptibility. QLT specimens exhibited the optimization of the strength and HE resistance with 6.7% filmy and stable reversed austenite, which could hinder the hydrogen diffusion, reduce local hydrogen concentration, delay the crack initiation and further arrest the crack propagation. Moreover, a 23% reduction in hydrogen embrittlement susceptibility of QLT specimens was achieved by comparing with quenching-tempering (QT)specimens. However, the interface of RA and matrix was a preferred site for crack initiation. • The role of "lamellarization" on the hydrogen embrittlement was investigated. • Both fraction and stability of revered austenite affected the HE behavior. • The interface of revered austenite and matrix is a preferred site for crack initiation. • The role of RA on the crack propagation was discussed. [ABSTRACT FROM AUTHOR]

Martensitic steels, engineered to meet automotive weight reduction and crashworthiness requirements, are highly susceptible to hydrogen embrittlement (HE). Despite extensive research to improve HE resistance, these steels remain vulnerable to HE after undergoing resistance spot welding (RSW). HE in spot-welded steels has been largely unexplored, and its underlying mechanism remains unclear. This study investigates the HE mechanism in RSWed steel sheets by examining microstructural alterations and hydrogen trapping sites before and after RSW. Additionally, the study analyzes variations in tensile-shear test (TST) properties relative to increasing hydrogen content. In spot-welded steels, the tensile-shear strength and fracture displacement decline as diffusible hydrogen levels increase. Specifically, fracture displacement sharply declines within the first 3 h of hydrogen charging, but this loss rate significantly decreases thereafter. This slope shift is attributed to a transition in the crack propagation path. Initially, cracks propagate along the fusion zone line, featuring transgranular failure. However, beyond a critical hydrogen content, crack propagation shifts to the prior austenite grain boundary (PAGB) in the upper critical heat-affected zone (UCHAZ), exhibiting intergranular failure. Consequently, when hydrogen content surpasses this critical threshold, the PAGB in the UCHAZ is weakened due to hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). Cracks then propagate along the PAGB in the direction of maximum stress during the tensile-shear test (TST), leading to a change in the crack propagation path. [Display omitted] • The resistance to hydrogen embrittlement for spot-welded advanced high strength steel is evaluated by tensile-shear test. • The difference in the behaviors of hydrogen embrittlement between steel matrix and welded part is compared. • The phenomenon of crack propagation path transition is observed over certain hydrogen content. • The mechanism of crack propagation path transition is discussed. [ABSTRACT FROM AUTHOR]

The biaxial compression experiments of rock-like materials with two flaws are carried out under different flaw inclination angle, rock bridge ligament angle, lateral stress. The experimental studies show that crack propagation modes of rock-like material are as follows: wing crack through mode (Y mode), shear crack through mode (J mode), mixed crack through mode (wing shear JY mode), longitudinal extension of crack and transverse shear splitting. prefabricated fractured rock specimens have experienced the closing stage of prefabricated fractures, the elastic deformation stage, the generation and expansion of cracks (or plastic strengthening), and the residual loading stage. The peak strength of the specimen is increases with the increase of flaw inclination angle and lateral stress. With the increase of the rock bridge ligament angle, the failure of the rock bridge region changes from the shear crack failure to composite failure of shear crack and the wing type tensile crack failure, and then to the wing crack failure. With the increase of the lateral pressure, the failure of the specimen changes from the wing type tensile crack failure to the wing type and shear crack failure, and then to shear crack failure. The flaw inclination angle mainly changes the form of crack growth but does not effect on the failure modes. The counting number of acoustic emission events at the center of the sample is relative large, indicating that the cacks appear in the part of the rock bridge firstly. With the increasing of loads, the cracks of the rock bridge expanding constantly and connecting finally. The changes of acoustic emission event counts is consistent with the macroscopic damage form obtained from the experiments. [ABSTRACT FROM AUTHOR]

The present study concerns the interface mode II fracture of hydroxyl functionalized multi‐walled carbon nanotubes (MWCNTs) reinforced carbon fiber epoxy composites. The well‐known cohesive zone model (CZM) is employed for investigating crack propagation. The major difficulty in applying the CZM is the parameter identification. In this work, the CZM's strength and energy parameters are determined reliably from the Short beam shear (SBS) and End‐notched flexure (ENF) tests, respectively, for pristine and three MWCNTs variations—0.1 wt.%, 0.2 wt.%, and 0.3 wt.%. The derived CZM parameters from the tests are imputed to a bilinear cohesive law to simulate the global load vs. displacement responses, which correlate well with the experimental findings. It is observed that the addition of 0.2 wt.% of MWCNTs increases the cohesive strength and fracture energy up to 14.14% and 17.78%, respectively, when compared to the pristine composites. Finally, the field emission scanning electron microscopy (FESEM) analysis is carried out to investigate the fracture mechanisms. Highlights: Cohesive properties under mode II are estimated using standard fracture tests.The homogenization technique is used to calculate the effective properties of CFRP.The maximum % error among the experimental and the numerical peak load is 3.01%.A higher density of hackles with an increase of MWCNTs up to 0.2 wt.%. [ABSTRACT FROM AUTHOR]

This work focuses on optimization of 3D printed bioinspired helicoidal composites in design space of helicoidal angle and brick aspect ratio under dynamic three‐point bending loading by performing gaussian process regression‐based Bayesian optimization method. Firstly, the impact responses and crack modes of helicoidal structures under dynamic three‐point bending loading were studied through experiments and simulations. Then, the helicoidal composites with better dynamic mechanical properties were obtained by iterations of Bayesian optimization based on gaussian process regression. Finally, the crack propagation modes of the optimized helicoidal structures under dynamic loading were investigated by analyzing the interlayer stress of the structure. The results show that the interlaminar shear stress of the optimized model is large, which is more prone to produce mixed mode I + II cracks. The mixed mode cracks cause crack deflection, which improving the fracture toughness of the structure. Highlights: Bioinspired 3D printed helicoidal composites are optimized by machine learning.The helicoidal composites with better dynamic mechanical properties are obtained.The crack propagation modes of the optimized helicoidal structures are investigated.The mixed mode I + II cracks cause crack deflection. [ABSTRACT FROM AUTHOR]

Nanoclay is considered to be one of the best fillers for reinforcement in structural polymer composites because of its low cost, easy availability, and ability to improve mechanical, thermal, corrosion resistance, barrier properties and nonflammability in corresponding nanocomposites. Pristine nanoclay is hydrophilic and therefore needs surface modification to make it compatible for uniform dispersion with polymer matrix. In the present work, montmorillonite nanoclay was protonated for generating more hydroxyl groups to facilitate silane functionalization and is reinforced to prepare epoxy nanocomposites with a varying content of 0.5 to 20 wt%. Studies are also conducted to investigate the effect of silanization of unprotonated nanoclay on epoxy nanocomposites. Interestingly, uniform highly exfoliated reduced‐size nanoclay platelets are obtained for functionalized protonated nanoclay. This behavior is attributed to the increase in the d‐spacing between the interlayers of the nanoclay during protonation and silanization. Tensile performances are found best with 0.5 wt% of silanized clay with an improvement of ~50%, ~84% and ~177% in strength, modulus and absorbed failure energy compared to neat epoxy. Although flexural and fracture performance are found highest with 2 wt% of silanized protonated clay with an improvement of ~57.5% in flexural strength and a remarkable ~241% and ~964% enhancement in fracture toughness and fracture energy compared to neat epoxy. The toughening mechanism investigation endorses the improvement in interfacial adhesion of the protonated silanized nanoclay that enhances the properties of the interfacial region, which significantly enhances the resistance for in‐panne crack propagation in epoxy nanocomposites. Highlights: Synthesized silanized and silanized protonated montmorillonite clay.Protonation facilitated silane moiety attachment onto nanoclay.Maximum improvement of flexural strength by ~57.5% for ESPrC2.KIC and GIC were highest showing ~1.74 MPam1/2 and ~830.28 J/m2 for ESPrC2.Enhanced interfacial adhesion due to SPrC with the epoxy matrix. [ABSTRACT FROM AUTHOR]

In this study, we promote a multi-scale modeling to predict the healing efficiencies (HEs) of incorporated polymers with self-healing microcapsules. The Python scripts were employed to generate three representative volume elements (RVEs) with randomly dispersed 5, 7.5, and 10% volume fraction (VF) of alginate microcapsules. Three VUSDFLD subroutines were codded and supplemented with ABAQUS/Explicit solver to obtain the maximum tensile stresses (Sut) of virgin, damaged, and healed samples followed by calculating HF of self-healing polymers. Based on the simulation results, more incorporation of self-healing microcapsules increased the tensile after impact HF, so that HFs were increased from 46.31% for RVEs containing 5% VF up to 65.41% and 84.84% for 7.5% and 10% VF, respectively. The presence of more self-healing microcapsules could improve the chance of rupturing more filled microcapsules with healing agents after crack propagation due to impact damages in the matrix. Thus, more damaged elements would be healed by spread healing agents. To evaluate the reliability of simulation results, the specimens containing electrosprayed multicore self-healing microcapsules were fabricated, and experimental HFs were calculated. The same trend was obtained for experimental results, as acquired in the simulation of RVEs. The error of healing efficiencies were only 6.82%, 2.81%, and 7.74 for incorporated specimens with 5, 7.5, and 10% VF of electrosprayed multicore microcapsules, respectively, indicating the accuracy of introduced multi-scale finite element modeling. The fabrication defects of experimental specimens can be the reason of simulation errors. [ABSTRACT FROM AUTHOR]

Varying external conditions in the metallogenetic process of crystalline rocks contribute to the complex mineral and textural characteristics, rendering the mechanical properties highly heterogeneous at the mineral scale. This research focused on the influences of minerals with relatively low strength and stiffness (soft minerals) in crystalline rocks on their cracking behavior. A particle‐based discrete element method (DEM) was first employed to establish random grain‐based models (GBM) of crystalline rocks containing soft minerals with different contents, strengths, and stiffnesses. On this basis, responses of the mechanical properties and crack propagation to these parameters were systematically investigated and an optimized micro‐parameter calibration method for real CT (computed‐tomography) ‐based GBM was then proposed considering the characteristics of soft minerals. The results demonstrate that with the decrease of the strength of soft mica, the intragranular cracks are prone to initiate and propagate inside the soft minerals and lead to the final crack coalescence. The decrease in the stiffness of soft minerals enhances their controlling effects on the cracking propagation. Based on the CT‐based granite model, it was found that a heterogeneous stress field is produced due to the spatial distribution of the soft (mica) and hard (quartz and feldspar) minerals, and the mica minerals tend to terminate cracks or force cracks to deflect or bypass individual grains during crack propagation. This study sheds light on the damage and failure processes of crystalline rocks with contrast mineral components. [ABSTRACT FROM AUTHOR]

The composite interlamination is the key part of load transfer and plays a decisive role in the overall mechanical performance of composite structures. The interlaminar property is predominantly influenced by the matrix resin which is easily affected by the hygrothermal environment. This paper delved into the effect of hygrothermal aging duration on the interlayer debonding behavior of unidirectional (UD) laminates. The pre‐cracked specimens were treated by hygrothermal aging with a period of 0, 15, 30, 60, 90, and 120 days. The double cantilever beam (DCB) tests were employed to evaluate the interlaminar property. The effect of hygrothermal aging on load–displacement responses, R‐curves, crack growth speed, and fracture surface topography was analyzed. The results revealed that the load‐bearing capacity of aged specimens presented a reduction of 18.6%–29.0% compared with unaged ones. The interlaminar fracture toughness of specimens subjected to 15 days of treatment decreased significantly compared with that of unaged specimens due to the increase of water absorption caused by hygrothermal aging. With the increase in hygrothermal aging time, the interlaminar fracture toughness peaked at 60 days because of the post‐curing effect, followed by a declining trend influenced by the dominant hygrothermal aging effect. The fiber bridging of aged samples was increasingly obvious, became the most prominent at 60 days, and then gradually reduced. The fiber bridging diminished the crack propagation speed, hindered interlaminar debonding, and contributed to the interlaminar toughening. Highlights: The samples underwent hygrothermal aging for 0, 15, 30, 60, 90, and 120 days.Load ability of aged samples was at least 18.6% lower than that of unaged ones.R‐curves rose before the crack length of 79 mm and then tended to stabilize.Fracture toughness first decreased, then increased and reduced with aging time.Fiber bridging could hinder crack growth and improve the interlayer property. [ABSTRACT FROM AUTHOR]

Background: The elastic–plastic fracture toughness (Jc) is an important mechanical parameter for studying the failure behavior of air plasma-sprayed (APS) thermal barrier coatings (TBC) at high temperatures. Objective: This study aims to: (1) develop an effective test method to characterize the Jc of TBC at high temperatures; (2) acquire accurate Jc data for TBC at high temperatures; (3) analyze the influence of plasticity of top-coat on the Jc characterization. Methods: The elastic–plastic Ramberg–Osgood equation of the ceramic top-coat and the deformation fields of single edge notched tension (SENT) specimens were measured by high-temperature in-situ tension with digital image correlation (DIC) system. The Jc of TBC was calculated by the numerical J-integral with DIC-measured (DIC-J) deformation fields by adopting Ramberg–Osgood equation of the top-coat. The finite element analysis (FEA) method was adopted to analyze the influence of plasticity of top-coat on the Jc characterization. Results: The curves of Jc varying with crack propagation length (Δa) of TBC were obtained and were expressed as JR = 24.47 × [ 1 + 1.0446 × ( Δ a ~ )0.7624] J/m2 and JR = 16.52 × [ 1 + 1.4806 × ( Δ a ~ )0.6742] J/m2 at 800 and 1000 ℃, respectively. Conclusions: A high-temperature in-situ tensile test of SENT specimens combined with the DIC-J method was developed to characterize Jc of TBC. The Jc of TBC displays a rising resistance curve behavior, and FEA results indicated that Jc would be underestimated without considering the plasticity of the top-coat at 800 and 1000 ℃. [ABSTRACT FROM AUTHOR]

In the present work, an atomistic scale investigation is done on crystalline silicon to understand the effect of crack depth from the loading (pulling) boundary on the critical near-tip state of stress. For various depths of embedded cracks, the near-tip stress field has been calculated at the critical state just before the crack propagation initiation. This atomistically calculated stress field is found to be quite close to those found using continuum linear elasticity. Thereafter, the critical stress intensity factor (SIF) is calculated for all cases by fitting the atomistically calculated normal stress over inverse square-rooted distance from the crack tip. It has been found that the closer the crack is located to the loading boundary (i.e., lesser depth), the lower is the (locally calculated) critical SIF. This implies that it is easier to initiate crack propagation when the crack is located closer to the loading boundary. The claim is also strengthened by a similar observation of (globally calculated) boundary stresses at the critical state just before crack propagation initiation. [ABSTRACT FROM AUTHOR]

A novel damage tolerance design method of discrete interleaved toughening for laminated composite was proposed. In this paper, discrete thermoplastic Polyamide-6,6 (PA 66) films were deployed at between the selected adjected layers, and three toughening dimensions were considered. Besides, three impact positions of specimens were tested under 5 J, 10 J, and 15 J, respectively. The impact behavior and compression after impact (CAI) of specimens were discussed and compared. Experimental results showed that delamination damage was suppressed in the process of propagation outwards across the toughened region, and the path of delamination crack propagation was changed and swerved. Therefore, the delamination damage projected area (DDPA) of all specimens were reduced by 21.09%–62.85%, compared with the non-toughened plate (base plate). In addition, the finding demonstrated that CAI strength is influenced by the delamination position and DDPA. The proposed method could improve the CAI strength by suppressing delamination and swerving the propagation path of delamination. Moreover, the CAI strength of all toughened plates were improved by 16.35%–61.94% in contrast to the related base plates. [ABSTRACT FROM AUTHOR]

The interaction mechanism of oppositely propagating cracks is an important basis for the study of rock fracture under dynamic loading. In this article, the stress field superposition and crack tip stress evolution are deeply investigated during the interaction of oppositely propagating cracks by using dynamic photoelastic experiment method and numerical simulation analysis. Obtained results indicate that the cracks interaction process is accompanied by the deflection of the crack, and the deflection of the cracks is mainly affected by the shear stress field at the crack tip. According to the difference of the crack deflection characteristics, the interaction process of the oppositely propagating cracks can be divided into two stages. The Stage I: the non-interlaced stage and Stage II: the interaction stage after the mutual staggered. It includes the period of Stage I that the oppositely propagating cracks are not interlaced with each other; the Stage II is the interaction period after the oppositely propagating cracks are interlaced with each other. The effects of stress intensity factor KI, stress intensity factor KII and far-field T stress on crack propagation process should be comprehensively considered when predicting the crack growth trajectory. The interaction of the stress field between cracks is the main factor determining the crack propagation trajectory. In addition, the vertical spacing between cracks also has a significant effect on the fracture behavior of oppositely propagating cracks. When the vertical distance between the two cracks is large, the local stress fields at the crack tip cannot overlap and interfere with each other, and the oppositely propagating cracks will expand independently of each other. [ABSTRACT FROM AUTHOR]

Novel Nb-Si-based alloys with heterogeneous layers that have the same composition (Nb-16 at.%Si) but different phase morphologies were designed in this work. Heterogeneous layered structure (HLS) was successfully fabricated in Nb-16Si alloys by layering composite powders after various degrees of mechanical alloying (6 h, 12 h, 18 h, and 24 h) alternately and subsequent spark plasma sintering (SPS). The influence of HLS on the fracture behavior at both room and elevated temperature was investigated via single-edge notched bending (SENB) and high-temperature compression, respectively. The results show that the diversified HLS is obtained by combining hard layers containing fine equiaxed crystals and/or soft ones with coarse lamellar niobium solid solution (Nbss). By affecting the crack propagation in SENB, HLS is favorable for improving the fracture toughness and exhibits a significant increase compared with the corresponding homogenous microstructure. Moreover, for the same HLS, a more excellent performance is achieved when the initial crack is located in the soft layer and extended across the interface to the hard one through crack bridging, crack deflection, crack branching, and shielding effect. Fracture starts in the soft layer (from powders of ball-milled for 12 h) of a 12–24 alloy, and a maximum KQ value (14.89 MPa·mm1/2) is consequently obtained, which is 33.8% higher than that of the homogeneous Nb-16Si alloy. Furthermore, the heterogeneous layered alloys display superior high-temperature compression strength, which is attributable to the dislocation multiplication and fine-grained structure. The proposed strategy in this study offers a promising route for fabricating Nb-Si-based alloys with optimized and improved mechanical properties to meet practical applications. [ABSTRACT FROM AUTHOR]

Calcareous mudstone, a type of red-bed soft rock, is prevalent in the surrounding rock of the Central Yunnan Water Diversion Project (CYWDP) in Yunnan Province, China, significantly impacting both construction and operation. The mechanical properties of calcareous mudstone vary with depth. This study investigates its mechanical properties, permeability characteristics, energy evolution, and macro- and micro-failure characteristics during deformation using triaxial compression tests under different confining pressures. Results reveal distinct stage characteristics in the stress–strain behavior, permeability, and energy evolution of calcareous mudstone. Crack propagation, permeability evolution, and energy dissipation are closely linked, elucidating the deformation and failure process, with fluid pressure playing a crucial role. The confining pressure σ3 increased from 2 MPa to 4 MPa and 6 MPa, while the peak stress σc (Pw = 1 MPa) of the calcareous mudstone increased by 84.49% and 24.89%, respectively. Conversely, the permeability at σc decreased from 11.25 × 10−17 m2 to 8.99 × 10−17 m2 and 5.72 × 10−17 m2, while the dissipative energy at σc increased from 12.39 kJ/m3 to 21.14 kJ/m3 and 42.51 kJ/m3. In comparison to those without fluid pressure (Pw = 0), the value of σc at Pw = 1 MPa was reduced by 36.61%, 23.23%, and 20.67% when σ3 was 2, 4, and 6 MPa, respectively. Increasing confining pressure augments characteristic stresses, deformation and failure energy, and ductility, while reducing permeability, crack propagation, and width. These findings enhance our understanding of calcareous mudstone properties at varying depths in tunnel construction scenarios. [ABSTRACT FROM AUTHOR]

Welded tuffs have a wide range of welding degrees and show significant variability in mechanical behavior. However, the detailed influence of welding degree on the meso-mechanical behavior of welded tuffs remains unclear. Based on petrographic and pore-structure analysis, we conducted a series of meso-mechanical experiments on weakly to strongly welded tuffs by utilizing a mesoscale real-time loading-observation-acquisition system. The results indicated that the strongly and weakly welded tuffs showed a small range in mineralogical composition and porosity, while the meso-mechanical behavior exhibited significant variability. Strongly welded tuffs showed lower uniaxial compression strength, weaker mechanical anisotropy, and smaller fracture surface roughness. In contrast, weakly welded tuffs exhibited higher uniaxial compression strength, stronger mechanical anisotropy, and rougher fracture surface roughness. Welded tuffs with strong packing and welding of glass shards tended to have fractures propagating along the maximum principal direction, while those with weak packing and welding of glass shards may have had failure along the alignment of glass shards. The influence of welding degree on the meso-mechanical behavior of welded tuffs probably originates from their diagenesis environments, mainly depending on the combined effect of the pyroclastic properties and pseudo-rhyolitic structure. The findings reveal the meso-mechanical differences of welded tuffs and shed light on improving tuffs for stable and durable construction. [ABSTRACT FROM AUTHOR]

Adding polypropylene fibre (PPF) to recycled aggregate concrete (RAC) not only improves performance but also has economic benefits. The effects of single-blend and double-blend micro- and macro-PPFs in RAC specimens were studied. Micro- and macro-PPFs were used to design and produce 30 groups of PPF-reinforced RAC specimens with 0%, 25% and 50% coarse aggregate (CA) substitution rates. Controlling the fibre mixing proportions, the stress–strain curve, elastic modulus, peak strength, peak strain and acoustic emission amplitude–frequency extremum (AFE) of each group of specimens were obtained. The elastic modulus and peak stress of specimens without PPFs decreases gradually with an increase of the CA substitution rate. However, there was a certain increase in elastic modulus and peak stress when PPFs were added. A damage constitutive model for PPF-reinforced RAC was established. By fitting this model, it was found that although the elastic modulus and peak stress of the RAC specimens increased by a certain extent, the fitting parameters of RAC were greater than those of ordinary concrete and the RAC post-peak strength was lower. The evolution law of acoustic emission AFE of PPF-reinforced RAC was studied. It was found that the cumulative AFE of RAC with PPF was larger, indicating that the PPFs limited crack propagation and increased the fracture energy. [ABSTRACT FROM AUTHOR]

To investigate the deformation and failure taw of deep sandstone, the relationship between plastic zone development, crack propagation and acoustic emission (ABE) characteristics is established. Tang deep sandstone samples as the research object, the axal static compression ABE test is charred out, the evolution law of plastic zone and maternal crack of rock samples is analyzed by numerical simulation. The results show that the dissipation of maternal energy density is relatively stable in the compaction and e!mastic stage,gradually increases in the hp!mastic stage, and all the energy is released immediately before allure. There is a strong core!nation between the hp!mastic zone and crack ABE characteristic.. The ranging count and energy Increase first and then decrease in the compaction stage. Before the elastic stage, the plastic zone and micro-cracks appear from both sides of the rock scamp! In the e!mastic stage, the ranging count and energy continue to increase,the Increase of the latter is greater than that of the former,the hp!mastic zone develops diagonally inward, and the number of cracks increases. In the hp!mastic stage, the ringing count continues to increase, the energy surges, and the plastic zone develops outwards. In the allure stage, both the ringing count and energy surge,and the simulation test shows a shape shear crack, which is consistent iii the actual allure crack. [ABSTRACT FROM AUTHOR]

In this work, the influence of the aspect ratio of graphene-based nanostructures (GBNs) and content on the mechanical properties of 3 mol% yttria tetragonal zirconia polycrystalline 3Y-TZP matrix composites was analysed. The influence of the dispersion method and sintering parameters on the flexural strength and elastic modulus of the composites was studied, and the fracture surfaces were characterized to determine the fracture mechanisms that occur. The results showed that small amounts of exfoliated graphene nanoplatelets, with reduced lateral size, and few layer graphene, up to 1.0 and 2.5 vol%, respectively, slightly increase the 3Y-TZP flexural strength. This has been attributed to the tortuosity of the crack propagation pathways and strengthening mechanisms. Higher contents cause a decrease in flexural strength and stiffness because of overlapped GBNs, which can promote the crack propagation. The pull-out of GBN was more significant in composites with non-exfoliated graphene nanoplatelets, where no increase on the flexural or biaxial strength was measured. [ABSTRACT FROM AUTHOR]

The intensive cluster fracturing technology is widely applied in deep shale reservoirs. However, field data show that the fracture initiation time and propagation length of each cluster are different, which causes significant non-uniformity and affects the fracturing results. In this paper, a hydraulic fracture asynchronous initiation and propagation model for deep shale gas is established based on mechanics theory, which can consider the influence of in-situ stress variation and stress interference effect on the fracture asynchronous initiation and propagation behavior. According to the model design parameters, deep shale hydraulic fractures are regulated and optimized in combination with the non-uniform flow-limiting perforation technology to achieve uniform fracture propagation. The results show that, the non-uniformity of each fracture is obvious using conventional uniform perforation. However, with non-uniform perforation, each cluster perforation number is adjusted, the difference of initiation time and each fracture propagation velocity is significantly reduced, and the length of all fractures tend to be basically the same. And the field monitoring data are in good agreement with the calculation results, which verifies the reliability of the model. This study can reduce design blindness of non-uniform flow-limiting perforation technique, and has an important theoretical guidance for the optimal design of fracturing. [ABSTRACT FROM AUTHOR]

Conglomerate reservoirs are important oil and gas resources that require hydraulic fracturing for stimulation. However, the heterogeneity of conglomerate rocks causes fractures to propagate irregularly, complicating the fracturing design. To provide insight into the complex fracture behavior in conglomerate rocks, a three-dimensional (3D) hydromechanical numerical model based on the discrete element method (DEM) was proposed in this study. Besides, a novel approach combining the grain-based DEM with Voronoi tessellation was adopted to depict the geometrical characteristics of conglomerate rocks. Considering the rock matrix-interface-gravel structure, the effects of various influencing factors including the strength and permeability, in situ stress difference, fluid properties and injection scheme on the fracture propagation and induced microseismic events were investigated. Two fracture behaviors, penetration and deflection, were summarized. Finally, the mechanisms of different fracture behaviors were discussed, revealing the joint effects of various factors on the fracture behavior. To predict the fracture behavior in conglomerate rocks, an explainable machine learning framework comprising the extreme gradient boosting and the shapley additive explanations was adopted, which attained high accuracy on the testing set. It can also provide comprehensive explanations for the predicted results, offering support for practical decisions. [ABSTRACT FROM AUTHOR]

This paper presents a forensic numerical study on hydro-fracturing at three locations within an excavation in a clayey till underlain by an aquifer in Ontario, Canada. The pioneering forensic studies were based on continuum mechanics using finite element method (FEM) combined with an effective medium approach, which did not explicitly simulate the physical process of fracture propagation. This has overestimated the size of the venting holes (i.e., model aperture approximately 8 m, observed approximately 0.1 m), hindering accurate assessment of the venting locations at the excavation base. For this reason, a coupled hydro-mechanical XFEM analysis, which explicitly models fracture propagation, was performed in this study to revisit the case history from the perspective of fracture mechanics. Parametric study is also performed to investigate the influence of flow rate on the direction of the fracture propagation, and thus location of venting holes. It is shown that the coupled hydro-mechanical XFEM analysis offers better predictions than previous FEM analysis for both, locations and sizes of the three observed venting holes. The parametric study reveals that an increase in the flow rate from 5 to 10 L/min (which is within the reported range) leads to a wider and less curved fracture, altering the predictions of the venting locations at the excavation base by around 8 m. This is because an increasing flow rate causes wider aperture and higher shear stress near the fracture tip, which intensifies the re-orientation of maximum principle stress that facilitates the re-direction of the propagating fractures. [ABSTRACT FROM AUTHOR]

This study presents a novel approach for simulating hydraulic fracture propagation in variably saturated porous media using the time sub-stepping method. Based on the authors' previous THM model, a variably saturated model is developed based on mixture theory using two independent variables of displacement and water pressure to describe the behavior of intact porous media. The proposed model adopts the crack as an interface element coupled to the general equilibrium and mass conservation equations. XFEM and β method are used to discretize the governing equations spatially and temporally, respectively. The time sub-stepping approach is used to unconstrain the crack tip advancement velocity to obtain a consistent solution. Three examples are solved to validate the model and show its robustness. The first two numerical examples are selected to demonstrate the capability of the proposed model to simulate consolidation and gravitational drainage in the variably saturated porous media. The third example studies crack propagation in an unsaturated porous plate. The time sub-stepping method finds when the crack propagates to an element ahead of the crack tip and smoothes the stepwise behavior for the quasi-static propagation of a single hydrofracture with longitudinal laminar flow. [ABSTRACT FROM AUTHOR]

We devised a mesoscopic model for recycled aggregates, enabling the deduction of mechanical behavior of finite element representative volume element (RVE) size from constituent properties like aggregate and mortar. This model can be integrated into a finite element solver as the material law, computing macroscopic properties based on individual constituents. It interprets material response under stress and strain by differentiating it into elastic and viscoplastic components. The elastic response uses a compressible neo-Hookean material model, while the viscoplastic response employs a nonassociated Perzyna-type model, accounting for rate-dependent deformation. We modified the Drucker–Prager yield function to predict fracture, and phase field equations describe fracture initiation and propagation. The model was applied to study fracture propagation in recycled aggregate concrete at a mesoscopic level, illustrating how fracture originates and spreads. After model calibration and validation, a parametric study examined the impact of residual mortar on an aggregate and new mortar matrix in the stress-strain relationship. Our investigation identified the significance of mechanical properties in the overall stress-strain relationship and failure patterns of recycled aggregate concrete (RAC), notably the new mortar matrix and old mortar adhesions. The model enables the prediction of fracture behavior in RAC with complex structural heterogeneity caused by recycled aggregates. [ABSTRACT FROM AUTHOR]

A three‐dimensional non‐isothermal phase field model of polycrystalline NiTi shape memory alloy (SMA) was established based on the Ginzburg–Landau's theory, which considered the interaction between crack growth and martensite transformation (MT). Then, the crack propagation of polycrystalline NiTi SMA and its dependence on the system's grain size and loading rate were studied by the phase field simulations. The results show that the proposed phase field model can characterize the MT behavior, temperature field changes, and stress‐displacement response of NiTi SMA during the crack growth with different grain sizes and loading rates. That is the higher the loading rate, the higher the fracture toughness is; the larger the grain size, the higher the fracture toughness is and the more significant the influence of grain boundary on the crack growth path becomes. Meanwhile, as the grain size increases, the fracture mode gradually changes from the transgranular fracture (for the fine‐grained alloy with a grain size ≈ 15 nm) to the intergranular one (for the coarse‐grained alloy with a grain size ≈ 100 nm). Highlights: The mechanisms for the rate dependence of crack propagation are clarified.The influence of the latent heat effect on crack propagation are clarified.The mechanisms for the toughening effects under different grain sizes are clarified.The mechanisms for the change in fracture mode are clarified. [ABSTRACT FROM AUTHOR]

For Ti alloys used in oil drilling pipe, the fatigue crack propagation (FCP) resistance is one of the key properties for petroleum industrial applications. In this work, the fatigue crack propagation behaviors of bimodal, equiaxed, lamellar, and Widmanstatten microstructures have been systematically investigated and characterized by SEM and EBSD. The results show that the Widmanstatten microstructure containing α colonies has higher yield strength (877 MPa), moderate elongation (9.3%), and better FCP resistance compared to other specimens. During the process of crack propagation, the large α colonies can effectively deflect the cracks and induce secondary cracks, which significantly impedes the main crack propagation. Additionally, 101¯2<101¯1¯> tensile twinning can occasionally occur within the large α colony along the crack, improving the plasticity of the crack tip and resulting in a decrease in fatigue crack propagation rate (FCPR). Highlights: Fatigue crack propagation behaviors of different microstructures were investigated.The Widmanstatten exhibits good tensile properties and crack propagation resistance.The 101¯2<101¯1¯> tensile twinning was found inside the large α colony along crack. [ABSTRACT FROM AUTHOR]

When the elastic‐brittle cracked body is subjected to compressive‐shear loading, not only does the phenomenon of wing crack initiation and propagation occur, but there is also a notable incidence of secondary crack initiation and propagation due to shear stress. Moreover, the shear fracture toughness (KIIc) predicted by the fracture criterion in the framework of classical fracture mechanics is usually smaller than the tensile fracture toughness (KIc), which is inconsistent with the actual observations. Therefore, this research firstly establishes a mechanical model of an elastic‐brittle cracked body under biaxial compression considering three kinds of crack parameters and materials' mechanical properties. Then, the stress field characteristics at the crack tip are analyzed. Next, a compression‐shear mixed fracture criterion is proposed. Finally, the effects of the lateral pressure coefficient (λ), critical plastic zone size (rc), friction coefficient (f), and deformation parameters of the crack surface on the failure modes at the crack tip are investigated. Highlights: A distinction is made between the failure and loading modes of the cracked rock mass.The stress field at the crack tip under compression and shear conditions is analyzed.A compression‐shear fracture criterion related to KIc and KIIc of materials is proposed.Conditions for the occurrence of shear failure at the crack tip are discussed. [ABSTRACT FROM AUTHOR]

The ability of wood–plastic composites (WPCs) to withstand various loads and resist plastic failure is attracting more and more interest due to the global increase in demand for WPCs by over 6 million tons per year. Among the most important and innovative research methods are those based on fracture mechanics—their results enable material designers to optimize the structures of these hybrid polymer composites at the nano, micro and macro levels, and they allow engineers to more accurately evaluate and select functional, sustainable, long-lasting and safe product designs. In this study, standard single-edge notched bending (SENB) tests were used to analyze the fracture toughness of two different extruded WPCs along the longitudinal (L) and transverse (T) directions of extrusion. In addition to their resistance to crack propagation, critical fracture criteria, initial contact stiffness, fracture parameters and fracture surfaces, the mechanical properties of these composites were also investigated. The results showed that WPC-A coded composites withstood higher loads until failure in both directions compared to WPC-B. Despite the larger data spread, both types of composites were more resistant to crack propagation in the T direction. Mode II of crack propagation was clearly visible, while mode III was not as pronounced. The experimental results and the numerical finite element (FE) model developed up to 58% of the maximum load correlated well, and the obtained deformation curves were best approximated using cubic equations (R2 > 0.99). The shear stress zone and its location, as well as the distribution of the equivalent stresses, had a major influence on crack propagation in the fracture process zone (FZP). [ABSTRACT FROM AUTHOR]

The research on the crack propagation mechanism of bone has important research significance and clinical medical value for the selection of cutting parameters and the development of new surgical tools. In this paper, an extended finite element method (X-FEM) model of ultrasonic bone cutting considering microstructure was developed to further study the ultrasonic bone cutting mechanism and to quantitatively analyze the effects of cutting direction, ultrasonic parameters, and cutting parameters on the mechanism of ultrasonic bone cutting crack propagation. The results show that ultrasonic bone cutting is essentially a controlled crack propagation process, in which brittle crack and fatigue crack are the main crack propagation mechanisms. In order to improve the efficiency of ultrasonic bone cutting, large amplitude and high-frequency ultrasonic vibration are preferred. Compared with the other two cutting directions, the crack propagation deflection angle in the transverse cutting direction is the largest, resulting in the worst cutting surface. Therefore, in the path planning of orthopedic surgical robots, the transverse cutting direction should be avoided as much as possible. Frequency only has a significant effect on the crack propagation rate and has a positive correlation. There is a positive correlation between the deflection angle, propagation length, propagation rate, and amplitude, which provides the possibility to control the direction and length of crack propagation by controlling the amplitude of ultrasonic. The feed speed is much lower than the ultrasonic vibration speed, which makes the influence of ultrasonic vibration speed on the crack propagation characteristics dominant. The X-FEM model of ultrasonic bone cutting provides an effective method for selecting reasonable machining parameters of orthopedic robot and optimize the design of ultrasonic osteotome. [ABSTRACT FROM AUTHOR]