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The stability of the roof in coal mining plays a crucial role in ensuring safe excavation. After coal extraction, the roof experiences complex and unbalanced stress conditions, leading to diverse roof failure behaviors, particularly in the case of thick roofs. This study examines the failure behaviors of roofs with different thicknesses through a combination of on-site measurements, physical modeling, and numerical modeling. The on-site results indicate that the failure of thick roof leads to larger magnitudes, increased magnitude variance, and energy compared to thin roof. A self-developed three-dimensional roof fracture experimental platform was utilized to conduct loading experiments on roofs with different thicknesses. The experimental results reveal that roof thickness significantly impacts peak load, deformation characteristics, crack patterns, and acoustic emission (AE) signals. Thin roof failure only generates tensile cracks, while thick roof failure produces both tensile and shear cracks. This suggests that an increase in roof thickness leads to a transition in the roof's failure mode from pure tensile failure to tensile-shear mixed failure or shear failure. The energy of AE events has a threshold. When below this threshold, more AE events occur for thin roofs, and when above it, thick roofs exhibit more AE events. The digital image correlation (DIC) results and AE location indicate roof failure initiates from the upper surface of the roof, where "O" shaped cracks form around the periphery, followed by gradual development of cracks on the lower surface. Thin roofs exhibit regular "X" shaped crack on lower surface, while thick roofs display additional branching and inflection points based on "X" shaped crack on lower surface. Numerical modeling using four polygonal particle roof models confirms the influence of roof thicknesses on peak load, deformation, and crack distribution, aligning with experimental and on-site results. These findings offer valuable theoretical support for controlling the stability of surrounding rock conditions in the presence of different roof thicknesses. Highlights: Roof thickness significantly affects coal mine safety, leading to diverse roof failure behaviors. On-site measurements, physical experiments, and numerical simulations reveal insights into roof behaviors. An experimental platform was established to explore the correlation between roof thickness and failure behavior. Thicker roofs exhibit higher peak loads, reduced deflection, complex crack propagation, and a tensile-shear mixed failure or shear failure. Numerical models of polygonal particle roofs further corroborate the impact of roof thickness on failure behavior, offering practical support for coal mine stability. [ABSTRACT FROM AUTHOR]

In this research, the cohesive length of various rock types is measured using quantitative fractography alongside a recently developed multifractal analysis. This length is then utilized to gauge material cohesive stress through the theory of critical distances. Furthermore, the fracture process zone length of different rings sourced from identical rocks is assessed as a function of ring dimensions and experimental measurements of fracture toughness, in accordance with the energy criterion of the finite fracture mechanics theory. Subsequently, employing the stress criterion within coupled finite fracture mechanics, the failure stress corresponding to the fracture process zone is determined for various rings. Ultimately, through interpolation, the critical stress corresponding to the cohesive length, quantified via quantitative fractography, is approximated. Remarkably, the cohesive stress values derived from both methodologies exhibit perfect alignment, indicating the successful determination of cohesive length for the analyzed rock materials. The study also delves into the significant implications of these findings, including the quantification of intrinsic tensile strength in quasi-brittle materials and the understanding of tensile strength variations under diverse stress concentrations and loading conditions. [ABSTRACT FROM AUTHOR]

The crown pillar in the stope structure belongs to the category of thick plate, and its thickness determines the stability of the engineering structure. The key to determining the safe thickness of the crown pillar lies in solving its deflection function. Previous researchers often used the Galerkin method and other methods except the Ritz method to solve the deflection function of the crown pillar under simple boundary conditions. However, these methods are difficult to solve for the deflection function of the crown pillar under complex boundary conditions. Therefore, this paper builds upon the Reissner plate theory and introduces the Ritz method while considering the influence of strain components εz, γyz, and γzx on the flexural deformation of the crown pillar. Thus, the Reissner–Ritz method for solving the deflection function of the crown pillar in the stope is developed. Taking the failure of the crown pillar in stope 27 in the + 280 m section of the Daxin Manganese Mine as an example, firstly, the maximum tensile stress of the crown pillar is compared with its tensile strength to determine the safe thickness of the crown pillar in stope 27. The correctness of the chosen safe thickness for the crown pillar in stope 27 is verified using the Reissner–Ritz method. Then, FLAC3D is used to model and analyze the 8 m thick crown pillar in stope 27, and the accuracy of the Reissner–Ritz method in determining the safe thickness of the crown pillar is verified through finite element analysis. Finally, a comparison is made between the Reissner–Ritz method and the Galerkin method in solving the deflection function of the crown pillar under the uniformly distributed load, considering both simple and complex boundary conditions. The research results show that the Reissner–Ritz method has significant advantages over the Galerkin method in solving the deflection function of the crown pillar under the uniformly distributed load, even under complex boundary conditions. The findings are of great significance for solving the deflection function of thick plates under both simple and complex boundary conditions under the uniformly distributed load and determining the safe thickness of thick plates. Highlights: Based on the Reissner thick plate theory, the Ritz method is introduced, taking into account the influence of strain components εz, γyz, and γzx on the bending deformation of the crown pillar, forming the Reissner–Ritz method for solving the deflection function of the crown pillar in the stope. The range of safe thickness values for the crown pillar is determined based on the thickness-span ratio and safety factor, incorporating engineering experience to finalize the safe thickness of the crown pillar in the stope. The accuracy of the Reissner–Ritz method in determining the safe thickness of the four-sided fixed support crown pillar under the uniformly distributed load is verified through finite element analysis. Comparing and analyzing the calculation results of the Reissner Ritz method with the Galerkin method. [ABSTRACT FROM AUTHOR]

Braided composite structures, characterized by their inherent brittleness, necessitate precise damage prediction and prevention to ensure structural integrity/reliability. This study introduces an innovative method for enhancing damage resistance in tubular triaxial hybrid braided composites. These composites employ Epoxy resin as the matrix, with polyester serving as the bias yarn, and glass and basalt as the axial yarns, woven at varying braiding angles. Tensile tests reveal a compelling trend: a reduction in the braiding angle correlates with an increase in the failure load, indicative of quasi‐ductile behavior. A model is also derived for predicting tensile elastic modulus, which demonstrates a strong correlation with experimental results. Furthermore, finite element simulations are utilized to analyze damage within the triaxial hybrid braided composite specimens, providing empirical confirmation of progressive damage occurrence. This research offers a promising avenue for designing/manufacturing advanced composite materials with superior damage‐resistance holding immense potential across a spectrum of engineering applications. Highlights: The tubular triaxial hybrid braided composites were produced by Epoxy resin as the matrix, with polyester as the bias yarn, and glass and basalt as the axial yarns at different braiding angles.An innovative method was introduced for enhancing damage resistance in tubular triaxial hybrid braided composites.The effect of operating parameters (braiding angle, type of bias yarns, production method) was investigated.Was tried to predict tensile modulus values in tubular triaxial hybrid braided composites by finite element simulation and developed equations.Finite element simulation exhibited excellent performance in the prediction of tensile behavior of structures manufactured by the innovative method. [ABSTRACT FROM AUTHOR]

Adhesive bonding plays a pivotal role in structural connections, yet the bonding strength is notably affected by the presence of pore defects. However, the invisibility of interior pores severely poses a challenge to understanding their influence on tensile failure behaviors under loading. In this study, we present a pioneering investigation into the real-time micro-failure mechanisms of adhesively bonded structures using in situ X-ray micro-CT. Moreover, the high-precision finite element analysis (FEA) of stress distribution is realized by establishing the real adhesive layer model based on micro-CT slices. The findings unveil that pores induce stress concentration within the adhesive layer during the tensile process, with stress levels significantly contingent upon pore sizes rather than their specific shapes. Consequently, larger pores initiate and propagate cracks along their paths, ultimately culminating in the failure of adhesively bonded structures. These outcomes serve as a significant stride in elucidating how pore defects affect the bonding performance of adhesively bonded structures, offering invaluable insights into their mechanisms. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) evaluation is an important Nondestructive Testing technique. The technique is a whole field passive technique that detects defects that are growing during the application of force on the structure. At a certain threshold, AE starts emanating from the structure while the structure is stressed by tensile deformation. 18% Ni Maraging steel 250 grade material is widely used in the aerospace industry and exhibits fracture behaviour. In the current study, tensile specimens are used and acoustic emission (AE) parameters are recorded. Four types of specimens Type A, Type B, Type C and Type D specimens are designated as heat -affected zone, parent metal, defect-free weldment and weld with notch defect, respectively. These specimens are tensile deformed in order to obtain AE parameters at 60% of failure load (FL), 60–75% of FL, 75–90% of FL and 90% to FL. AE parameters – amplitude, ring down counts, duration, rise time, energy, RA value, DA value, hit rate, count rate and energy rate – are tabulated for various FLs. These parameters have vital importance in critical assessment of the structural integrity of 18% Ni Maraging steel 250 structures. [ABSTRACT FROM AUTHOR]

To study the dynamics of a single fiber tensile break within an S-Glass/epoxy composite and the associated effects of stress wave propagation in the fibers, interface and matrix, a 3D micromechanical Finite Element (FE) model with a hexagonal packing of parallel fibers is developed. The effects of a dynamic fiber break on energy dissipation associated with resin plasticity and interface debonding using cohesive traction laws are included. The 3D FE model also incorporates process-induced residual stresses that induces radial compression at the fiber-matrix interface due the mismatch in CTE and Poisson's ratios between the fiber and matrix. During dynamic fiber failure where interface debonding occurs, radial compressive residual stresses lead to additional frictional energy dissipation in the debond region of the interface. A map of the dynamic stress concentration factor (SCF) values on the surface (along the axial as well as circumferential directions) of the fibers which are neighboring the fiber break is generated. A stability criterion based on an energy balance between elastic strain energy released by the fiber and energy dissipation (resin plasticity, interphase debonding and frictional sliding) is established to predict maximum fiber strength that initiates unstable debonding of the interface characteristic of axial splitting of the unidirectional composite loaded in tension. The FE modeling results also indicate that the dynamic fiber break introduces strain rates on the order of 106/s in the fiber and matrix, and up to 1012/s in the interphase. [ABSTRACT FROM AUTHOR]

Non-linear finite element (FE) analysis is a powerful tool for determination of ultimate capacities of steel components. To produce reliable predictions of structural strength, it is of fundamental importance that non-linear finite element analyses are based on a validated methodology. This paper focuses on physical test campaigns, which are designed with the purpose of providing an experimental foundation for calibrated and validated non-linear finite element assessments of plated components, which form part of typical offshore structures. The experimental work discussed in the current paper is a continuation of the experiments of tubular members and joints, which were carried out by Maersk Oil in the late nineties. The objective is that the two-test campaigns together shall allow for development of a non-linear finite element methodology with calibrated failure criteria providing either characteristic or mean level of capacity/response for the main details in typical offshore structures. This paper particularly focuses on the testing campaign completed in 2017 which forms the basis for the calibration of the failure criteria covering plated sections. [ABSTRACT FROM AUTHOR]

The induction welding has been recognized as one of potential and high-efficiency joining methods for thermoplastic composite materials. In this study, a numerical simulation model with containing both induction wielding heat transfer and joint tensile failure process for CF/PPS-Al alloy interlocking induction welding was established based on software COMSOL Multiphysics and Abaqus/Explicit. The CF/PPS-Al7075 interlocking welding joints with special designed macro-scale interlocking were tested under tensile loads, and the corresponding single-lap shear strength, energy absorption, and failure mechanisms were investigated by combining the experimental and numerical approaches. Finally, the influence of macro-scale interlocking geometric parameters on joint tensile strength was also discussed. The results indicate that the proposed model can effectively predict the temperature distribution in the welding process and the tensile failure process of the joint. It is also presented that the addition of macro-scale interlocking features can effectively improve the ultimate load (47%) of the CF/PPS-Al alloy induction welded joints. Meanwhile, the number of addition PPS films in the welding zone and the inclination angle have greater contribution on the tensile strength of the welded joints. [ABSTRACT FROM AUTHOR]

Geotextile layers are arranged on and below the geomembrane to prevent the geomembrane from being punctured and damaged. The geotextile not only plays a role in physical protection, like anti-puncture but also makes a great difference to the mechanical properties of the geomembrane's air expansion deformation. In this paper, the bulging deformation of geotextile is simplified as spherical bulging deformation under ring-restrained conditions. Using the special bulging deformation test equipment, the bulging deformation experiment of geotextile is realized, the main factors affecting the bulging deformation are analyzed, the law of bulging deformation and failure of geotextile is summarized, the failure mechanism of geotextile and the Influence of geotextile on the properties of geomembrane are discussed, and the following conclusions are drawn. The failure of bulging deformation of geotextiles belongs to tensile failure, which is characterized by fast speed and high strength. The typical failure mode is spindle-shaped cracks distributed along the crown, whose failure mechanism belongs to tensile failure produced in weak areas. The bulging deformation of the geotextile shows nonuniformity, with the largest deformation at the crown top and the smallest deformation at the ring constraint. When the geotextile is covered on the geomembrane, bulging pressure is shared by both the geomembrane and the geotextile. At the initial deformation stage, the geomembrane replaces it, and then the geotextile bears more internal pressure and plays a decisive role till destruction. [ABSTRACT FROM AUTHOR]

To enhance understanding of the dynamic tensile failure mechanism of MgO-C refractories, the Split Hopkinson Pressure Bar test combined with digital image correlation techniques were utilized. The dynamic failure behavior of specimens with different heat treatments and graphite content was investigated under various impact velocities. The MgO-C specimens exhibit severer damage and a more tortuous crack path with higher impact velocity. The SiC and forsterite phases generate during heat treatment are advantageous in inhibiting crack propagation, while the formation of oxide layer makes the material more susceptible to brittle fracture. Due to the presence of microcracks, high graphite samples lead to a reduction in tensile strength, but result in a wider fracture zone, which dissipates impact energy. Compared with the significant increase of strength under compressive impact loading, the critical tensile strain rate of MgO-C is easier to achieve after which the tensile strength decreases. [ABSTRACT FROM AUTHOR]

Adhesive joints possess a number of advantages over traditional joining methods and are widely used in composite structures. Conventional non-destructive examination techniques do not readily reveal joint degradation before the formation of explicit defects. Embedded fiber Bragg grating (FBG) sensors and the resistance of carbon nanotube (CNT)-doped conductive joints have been proposed to monitor the structural integrity of adhesive joints. Both techniques will be employed and compared in the current work to monitor damage development in adhesive joints under tensile and cyclic fatigue loading. Most of the previous works took measurements under an applied load, which by itself will affect the monitoring signals without the presence of any damage. Moreover, most FBG works primarily relied on the peak shifting phenomenon for sensing. Degradation of adhesive and inter-facial defects will lead to non-uniform strain that may chirp the FBG spectrum, causing complications in the peak shifting measurement. In view of the above shortfalls, measurements are made at some low and fixed loads to preclude any unwanted effect due to the applied load. The whole FBG spectrum, instead of a single peak, will be used, and a quantitative parameter to describe spectrum changes is proposed for monitoring purposes. The extent of damage is revealed by a fluorescent penetrant and correlated with the monitoring signals. With these refined techniques, we hope to shed some light on the relative merits and limitations of the two techniques. [ABSTRACT FROM AUTHOR]

Anchored bolts are well known as an effective measure to support the rock masses, after all with stiff steel bolts being inserted into them. Although numerous researches have been carried out on anchored joints, the effects of anchored bolts on rock mass containing nonpersistent joints were rarely investigated. In the present study, in order to make up for the deficiency of research, we carried out experimental study on the effect of anchored bolts on failure and strength behavior of nonpersistent jointed rock model. Specifically, the unbolted and bolted rocklike samples with one set of nonpersistent joints were carefully prepared and subjected to the uniaxial compression tests. The strength and failure behavior of jointed rock mass with/without bolts were systematically compared and analyzed. The results demonstrated the effect of joint dip angle and joint spacing on the failure behavior of jointed rock model. The anchored bolts mainly increased the strength of jointed samples having joints of intermediate dip angles such as α = 30°, 45°, and 60°, which fail in a mechanism of Shear Failure along the Joint Plane. The anchored bolts support the jointed rock models through providing lateral constraints and “pin” effect. Even though the anchored bolts work better for the intermediate dip angle situations to increase the bearing capability than for low dip angle (e.g., α = 0° and 15°) and high dip angle (e.g., α = 75° and 90°), they provide limit support strength such that cannot eliminate the influence of nonpersistent joints. [ABSTRACT FROM AUTHOR]

Tensile crack-induced collapse is widely distributed in major mountainous areas of China, often result in sudden and catastrophic consequences due to the rapid movement of the falling bodies. To better understand the development of tensile crack-induced collapses, the phase field method, originally used for studying brittle fracturing, has been further applied in this research. Firstly, the application of the phase field method in modeling rock tensile failure is validated, demonstrating its effectiveness. The rationality of applying the phase field method for analyzing tensile crack-induced collapses has been thoroughly investigated, and solutions to address phase field disorder have been proposed. By incorporating heterogeneity features and implementing a prefabricated crack, both approaches can effectively address the issue of phase field disorder. However, the latter method aligns more closely with engineering practices. The present study provides a comprehensive investigation into the development of tensile crack-induced collapses with varying cavity morphologies. The corresponding change laws of tensile crack-induced collapses are systematically analyzed and summarized. Moreover, novel stability evaluation parameters, including reduction coefficients and safety points, are proposed and successfully applied in calculations. Our research on different cave morphologies has shown that the depth and shape of a cave, as well as the thickness and center of gravity of protruding rock masses, significantly influence the development process of tensile crack-induced collapse. This approach facilitates a comprehensive examination of the fracture process and yields valuable insights into the mechanics underlying tensile crack-induced collapses. [ABSTRACT FROM AUTHOR]

The investigation into the effects of acidizing treatment on the mechanical property of hot dry rocks (HDR) is beneficial for our understanding of the fracturing and stimulation mechanisms in HDR reservoirs. In this article, Brazilian disk tests were first carried out for hollow hot dry rocks with different internal diameters after acidizing treatments. The influences of acidizing treatments on the physical properties, tensile strength, and failure patterns of hot dry rock specimens were presented. Besides, the effects of the diameter of the internal hole on the peak load and failure patterns of the hot dry rock specimens were also investigated. The peak load decreases with the increase in the internal diameter. The results indicated that the acidizing treatments can dissolute the minerals, decrease rock mass, and tensile strength. The investigation of failure patterns demonstrated that the acidizing treatment is beneficial for the fracturing of hot dry rocks. The present study can provide some basic and theoretical data for the development of geothermal reservoir. [ABSTRACT FROM AUTHOR]

The rate-dependent tensile failure of rock with a cement inclusion was experimentally and numerically investigated to reveal the coupled dynamic response of inclusion-containing heterogeneous rock structures. Brazilian discs (BDs) with differently sized inclusion cores made of Portland cement were compressed using a split Hopkinson pressure bar loading system. The inclusions in the BD specimens changed the observed failure patterns compared to the splitting results observed in traditional monolithic rock BDs. The failure patterns observed in the composite rock–cement depend on the loading rate, inclusion size, and material strengths. The tensile BD failure patterns fall into three classes: single and double deflection along the interface with the inclusion and direct penetration through the heterogeneous structure. As the inclusion diameter or loading rate is increased, the failure pattern of the BD generally evolves from single to double deflection to penetration. The mechanism underlying the formation of the different failure patterns was further investigated using discrete element modelling. This paper may improve our understanding of the effect of loading rate on the failure and fracture behaviour of heterogeneous rock structures under tension. Highlights: Static and dynamic tensile failure characteristics of inclusion-containing rock heterogeneous structure were experimentally and numerically investigated. Failure patterns were classified into three categories in terms of loading rate and normalised inclusion diameter. The mechanism and threshold of different failure patterns were given with the assistance of DEM simulation. [ABSTRACT FROM AUTHOR]

A high degree of alteration causes swelling, disintegration and argillization of granite and thus weakens its physical and mechanical properties. Very few experimental studies, however, have been conducted to quantitatively characterize the strong-to-weak transition of the mechanical behaviours of granite affected by varying degrees of alteration. A new miniature tensile instrument system, which can visualize the failure process and simultaneously record the stress–strain curves, was utilized to test the tensile strength of dog-bone sliced samples of altered granite. Meanwhile, an improved quantitative method was proposed to characterize the alteration degree. The results demonstrate that the tensile strength of granite decreases significantly with increasing alteration rate, while the strain at the peak strength and fracture angle increase. Additionally, the orientation of weaker crystals and the mineral size distribution significantly affect fracture propagation. But the effect will be weakened as the alteration rate increases. On the basis of fracture angle, tensile peak strength, strain at peak strength, and microscopy images of crack initiation and propagation, three major classes of fractures are identified from the test results: (1) extension fracture at a low alteration rate: crack initiates and propagates along biotite-brittle mineral interfaces; (2) shear fracture at a high alteration rate: intragranular crack initiates within altered feldspar and propagates along the interior of altered mineral grains; (3) hybrid fracture at a moderate alteration rate: the above two failure phenomena coexist. A simple model that considers the fracture process of altered granite was proposed to explain the transition from extension fracture to shear fracture. Highlights: A new visual miniature tensile instrument is utilized to capture the crack initiation and propagation. An improved quantitative method is proposed to characterize the alteration degree of granite. As alteration degree increases, the tensile strength of granite significantly decreases, whereas both the strain and the fracture angle increase. The transition from extension fracture to shear fracture of altered granite is detected. [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]

Salt rock, mudstone, and glauberite are three typical rocks of the salt cavern gas storage. In order to obtain the rocks’ characteristic parameters of acoustic emission under the stretching test, the Brazilian split test and acoustic emission test were carried out. The results show that among the three rocks, salt rock’s strength is the lowest, with peak stress of 1.27 MPa, which is less than 1/2 of mudstone and slightly lower than glauberite. The maximum strain salt rock corresponding to the peak stress is 0.007 6, which is 1.5 times larger than mudstone and more than 2 times that of glauberite. Among the three rocks, the maximum number of acoustic emission events for salt rock is 10 148, mudstone is 119, and glauberite is 1 166. The salt rock first appears the acoustic emission event point at the cushion, while the mudstone and glauberite appears in the middle part of the sample and extended towards both ends along the loading direction. The energy rate and the ringing count rate of three rocks increases significantly during the yield deformation stage. The cumulative energy and cumulative ringing count of the salt rock rose in the form of a smooth curve, which the curve of the mudstone is stepped, and the glauberite is steep near the peak stress. The maximum average energy and ringing count of salt rock is 2.02×10-14 J and 1 200.6 times. Mudstone is similar to glauberite, of which difference between salt rock is large. [ABSTRACT FROM AUTHOR]

Inherent microcrack populations have a significant effect on the fracture behaviour of natural rocks. The present study addresses this topic in numerical simulations of uniaxial tension and three-point bending tests. For this end, a rock fracture model based on multiple intersecting embedded discontinuity finite elements is developed. The inherent (pre-existing) microcrack populations are represented by pre-embedded randomly oriented discontinuity populations. Crack shielding (through spurious locking) is prevented by allowing a new crack to be introduced, upon violation of the Rankine criterion, in an element with an initial crack unfavourably oriented to the loading direction. Rock heterogeneity is accounted for by random clusters of triangular finite elements representing different minerals of granitic numerical rock. Numerical simulations demonstrate the strength lowering effect of initial microcrack populations. This effect is substantially stronger under uniaxial tension, due to the uniform stress state, than in semicircular three-point bending having a non-uniform stress state with a clear local maximum of tensile stress. [ABSTRACT FROM AUTHOR]

In situ synchrotron radiation computed tomography (SRCT) was used to compare the fibre damage progression in five configurations of (902/02)s carbon-epoxy coupons loaded to failure. The effects of different sizing types, surface treatments and fibre diameters on the macroscopic properties, for example, ultimate tensile strength (UTS), and on the damage accumulation at a microscopic scale, for example, fibre break accumulation, were assessed. A semi-automated approach was adopted to process the large amount of data obtained from the SRCT scans and further method applicability areas can be envisaged. Single fibre break accumulation was seen to be influenced by the fibre type, while the formation of interacting fibre break groups by the surface treatment and the sizing type. For the materials presented, it can be suggested that an increased defect tolerance can be obtained by moving from stronger to weaker fibre-matrix adhesion, with sub-critical multiplet behaviour emerging as independent of the average UTS value. [ABSTRACT FROM AUTHOR]

In this paper, upper bound limit analysis that includes a horizontal pseudostatic seismic force is used for the first time to obtain the limit load on strip footings seated on cohesive-frictional soils reinforced with a single geosynthetic layer. Reinforcement tensile rupture and sliding failure modes for the geosynthetic layer are included in the analyses. Results of analyses are presented as optimum reinforcement depths and a bearing capacity equation with a single term and different bearing capacity factors for tensile rupture and sliding failure modes. The bearing capacity factors are presented in tables and capture the combined influence of the reinforcement strength, soil frictional strength and cohesion, soil unit weight, footing geometry, uniform surcharge, and magnitude of horizontal ground acceleration. [ABSTRACT FROM AUTHOR]

The failure process of the open-pored T300/1034-C carbon fiber composite laminate with a ply angle of [ 00 I ( ± 45°) /3 ( 90° ) 3]s under tensile load was studied by using 2-D shell elements and 3-D solid elements in the ABAQUS finite element software. First, the shell element and continuous shell element carbon fiber composite material models were established with the ABAQUS finite element software, and the internal failure of the layer was simulated using the built-in 2-D Hashin criterion and degradation model. However, the 2-D model did not consider the interaction between the failures of each layer, and by writing the material subroutine VUMAT, the 3-D Hashin criterion and the equivalent stress-strain bilinear degradation method based on the fracture energy were introduced, and the solid element was used to simulate the carbon fiber composite material failure behavior. Through the simulation of three element models, the results showed that the stress concentration caused by the opening will make the fiber and matrix of the laminate more likely to fail during the stretching process and become the source of cracks; during the failure process of laminates, they all show a failure development trend from " X-shape" to "hourglass-shape", and eventually break in the width direction; compared with the traditional shell element and continuous shell element, the simulation accuracy of the solid model is closer to the experimental value. The simulation limit failure loads of the three elements differ from the literature data by 26. 1%, 31. 1%, and 8. 64%, respectively. [ABSTRACT FROM AUTHOR]

The paper presents a novel family of strain-based beam finite elements (FE) for analysis of tensile failure of a reinforced concrete bar (RC bar), with results of the analysis being independent of the applied FE mesh. The composite bar consists of a continuous longitudinal ductile reinforcing bar(s) surrounded by brittle concrete cover, which are considered separately in the model. Longitudinal slip at the contact between the concrete cover and reinforcing bars is allowed, while their relative displacements perpendicular to the axis of the RC bar are prevented. Cracks in concrete cover occur when tensile stress in concrete exceeds its tensile strength. Propagation of partially connected crack, that is, softening of the material at the crack, is described through constitutive law in form of nonlinear relationship between stresses in concrete at the crack and the width of the crack. Each separate crack is considered discretely as a discontinuity in geometry of the element. In the analysis of cracking of concrete, it is commonly assumed that the discrete crack can occur at the nodes of FE only. However, this assumption leads to dependence of the analysis results on the employed FE mesh. The presented family of FE enables occurrence of the crack anywhere along the FE. In order to achieve this, the discrete crack is excluded from equations of FE and additional boundary conditions are introduced at the discontinuity. This approach ensures that the location of the cracks, their number and their propagation are independent of the applied FE mesh. Advantages of the novel family of FE are thoroughly presented in a parametric study which investigates influence of number of FE as well as influence of degrees of interpolation and integration on the cracking of RC bar under tensile loading. Experimental results of tensile tests on the analysed bar are available in literature. It can be concluded that the results obtained with the minimal possible number of novel FE and sufficiently high degree of numerical integration scheme, applied for solving integrals in equations of FE, are considerably more accurate than the results of previous analyses with model of discrete crack at the nodes of FE only. [ABSTRACT FROM AUTHOR]

Shape memory polymer composite (SMPC) exhibits the remarkable mechanical properties as compared to its corresponding shape memory polymer (SMP) without compromising the shape memory behavior. The enhancement of the mechanical and thermomechanical properties of the carbon fiber-reinforced SMPC is presented in the present study with the incorporation of graphene nanoplatelets (GnP) in the SMP matrix. The fabrication process involved the preparation of the GnP/epoxy nanocomposites through ultrasonication and shear mixing and the subsequent molding of the carbon fiber-reinforced hybrid polymer composites by hand layup technique. The mechanical and thermomechanical characterizations were conducted as per the ASTM standards, which were followed with corresponding morphological study to the explore the microscale behavior of the hybrid composites. Shape memory behavior were studied in terms of the shape recovery ( R r ) and shape fixity ( R f ) through the heat activation bending tests. The tensile strength of the hybrid composites with 0.4 and 0.6 wt% GnP content increased by 14.3% and 32.2%, respectively, as compared to unmodified SMPC. Similar trends were also indicated in the dynamic mechanical analysis (DMA) with the corresponding rise in the storage modulus and glass transition temperature due to incorporation of nanofillers. The improvement of the interfacial bonding between the fiber and matrix and wettability of carbon fiber supported these improvements. Negligible adverse effect was noticed in the shape memory behavior of the hybrid composites with the incorporation of GnP, which displayed the R r and R f of ~97% and 96%, respectively. [ABSTRACT FROM AUTHOR]

Classical analyses of basal crevasse opening do not account for the free surface of a floating ice layer. We describe a high‐resolution numerical treatment of the opening of a single crevasse in a finite thickness elastic layer floating on an inviscid substrate. For low extensional stress (less than about half of the expected maximum for a freely floating shelf) the resulting crevasse height and width match previous studies. For larger magnitude applied extensional stresses, the new results predict basal crevasse widths an order of magnitude greater than the classical solution. An analysis using the thin‐layer approximation shows that the greatly increased predicted width of basal crevasse opening results from layer bending. Given that the height and width of basal crevasses are non‐linear functions of the stress experienced by an ice shelf, the new model results may enable better estimation of buttressing stresses for different parts of ice shelves. Plain Language Summary: Basal crevasses are water filled cracks the cut through much of the ice shelves and so contribute to their breakup. A new analysis shows that basal crevasses can break through significantly more of a floating ice layer than previous models that could not consider the bending of the ice layer. This more consistent approach suggests that basal crevasses can be an order of magnitude wider than estimated by the earlier studies. A simple analytic description of flexure of ice layers correctly predicts the maximum width of basal crevasses. Key Points: The first numerical analysis of basal crevasse opening including ice shelf bending is presentedBasal crevasses can be an order of magnitude wider than predicted by classical studiesAn analytic thin elastic plate description matches the numerical results in terms of crevasse width for a freely floating ice layer [ABSTRACT FROM AUTHOR]

Hard rock often performs as brittle failures, such as cracking, spalling, and rockburst, induced by excavation in deep underground engineering. To understand the effect of the minimum principal stress and unloading rate on the spalling and rockburst of marble, unloading experiments were carried out by using true triaxial equipment combined with a high-speed camera, acoustic emission instrumentation, and scanning electron microscope. The experimental results showed that the failure process of marble specimens was more stable and less inclined to exhibit dynamic ejection with a low strain energy release per unit time under a low unloading rate. At the same time, the initial minimum principal stress controlled the marble's failure mode by changing its mode from predominantly shear failure to shear-tension failure as the minimum principal stress decreased, similar to the spalling behaviors of surrounding rock observed in the underground tunnel. What's more, the dynamic rockburst of the marble specimen was simulated under the condition with a high unloading rate, high initial minimum principal, and free face on the specimen. Based on these experimental investigations, a flowchart was also presented to estimate the possible failure mode of marble specimens under different initial minimum principal stress and unloading rate conditions, which would be conducive to the disaster prevention of hard rock in deep underground engineering. [ABSTRACT FROM AUTHOR]

In the present work, an attempt has been made to study the mechanical behavior and tensile fractography of 40- and 90-micron-sized boron carbide (B4C) particulate-reinforced light metal (LM) 29 alloy composites. LM29 alloy with 3, 6 and 9 wt. % of 40- and 90-micron-sized B4C composites was synthesized by liquid stir method. Microstructural analyses were obtained by using scanning electron micrographs and energy-dispersive spectrographs. Mechanical properties like hardness, ultimate, yield strength and ductility were evaluated as per American Society for Testing and Materials standards. Scanning electron microscope micrographs show the even dispersal of B4C particulates in the LM29 alloy, and this is confirmed by energy-dispersive spectroscopy analysis. Further, hardness, ultimate and yield strength of matrix LM29 alloy were enriched with the addition of B4C reinforcement and were more in the case of 40-micron-sized reinforced composites. There was small decrease in ductility of composites in both cases. [ABSTRACT FROM AUTHOR]

The seismic responses of asphalt slabs in asphalt concrete-faced rockfill dams (ACFRDs) under the oblique incidence of seismic waves and the effect of a high strain rate on failure evaluation are still understudied. In this paper, formulas for the free field of SV waves at arbitrary incident angles are derived, a wave input model for SV wave spatial oblique incidence is established, and a method is proposed for assessing the failure of asphalt slabs. In this method, the real-time change in the tensile strength as it relates to the strain rate is considered. Taking an actual ACFRD as the research object, 16 obliquely incident SV wave conditions with different azimuthal and oblique incidence angles are considered, the influences of the incidence angle on the seismic response of an asphalt slab are analyzed in terms of the stress and acceleration, and the differences between the static and dynamic damage assessment methods are explored. The results show that the established SV-wave spatial oblique incident wave input model can accurately simulate the free-field half-space. The numerical solution of the wave input agrees well with the analytical solution. Compared with that of the vertical input, the maximum acceleration of the slab in the axial and vertical directions increased for 13 of the 15 oblique incidence conditions. The spatially oblique input leads to an increase in the dynamic stresses on the slabs, with the maximum tensile and compressive stresses increasing by 63 % and 153 %, respectively. Neglecting the oblique incidence of seismic motion may result in a significant underestimation of the seismic response of the slab. Moreover, the traditional method of increasing the static strength by 20 % as a criterion for determining the strength of slab tensile failure is overly strict. [ABSTRACT FROM AUTHOR]

Edge-to-edge is the most common form of contact in a two-dimensional joint block system. Discontinuous deformation analysis (DDA) is a powerful tool for handling block systems and treats an edge-to-edge contact as two vertex-to-edge contacts with a couple of normal and shear springs at the extremes of the contact segment. However, this method is unsuitable for evaluating the tensile failure of a joint under asymmetrical tension conditions, even though it can simplify the contact type and increase computational efficiency. This is mainly because the distributed forces at an edge-to-edge contact are simplified as two couples of concentrated forces. To solve this problem, this paper proposes incorporating a multi-spring edge-to-edge contact model with DDA. In the model, several contact pairs with normal and shear springs on an edge-to-edge contact are set to simulate the distributed forces. Several benchmark tests were performed to demonstrate the discrepancy between the original and improved DDAs. The results revealed that the latter more accurately models the stress distribution across the edge-to-edge contact, providing a more reasonable acceleration required to topple a series of blocks resting on an inclined stepped base. [ABSTRACT FROM AUTHOR]

In slope stability evaluation, it is common that a potential tensile sliding surface is not accurately positioned. In this paper, the strength reduction method considering shear and tensile failure with a strain-softening model is adopted to simulate the deterioration of the strength parameters of geomaterials during failure. Based on the initial stress method, a new quantitative display index of the full sliding surface is proposed. This method was applied to the stability analysis of a heterogeneous slope and a homogeneous slope. The results show that the plastic zone determined with the strain-softening model is much smaller than that determined with the Mohr-Coulomb model, and the difference is 34–40%. The safety factor obtained without considering tensile failure is 3.1% larger than that obtained considering tensile failure. The index can be used to quantitatively display the shear failure zone and tensile failure zone of a sliding surface. [ABSTRACT FROM AUTHOR]

Compressional wave velocity measurements and cone penetration tests were carried out for pressure cores recovered from the Krishna–Godavari Basin off the eastern coast of India, using an instrumented pressure testing chamber constructed by the Japanese National Institute of Advanced Industrial Science and Technology. For pressure cores with high gas hydrate saturations (S h) and exhibited high compressional wave velocities also display a high loading force that resulted in tensile failure. A pressure core sample with low compressional wave velocities and low gas hydrate saturations led to a low loading force, which resulted in radial shear. The cone factor connecting the cone resistance and the undrained shear strength, N k , was estimated using cone penetration testing and the uniaxial compressional results. We estimated its value as N k = 45 by using a uniaxial compression loading speed of 0.01%/min and a cone insertion loading speed of 0.25 mm/s. Undrained shear strengths, estimated from cone penetration results using N k = 45, were assumed to be equal to the tensile strengths between hydrate-hydrate and hydrate-particle interface when S h is less than 50% and increases when S h is more than 50% assuming that gas hydrate morphology was matrix supporting. • Compressional wave velocity measurements and cone penetration tests were applied to pressure cores. • Failure modes of pressure cores were assessed after cone penetration testing. • The cone factor for pressure cores was estimated to be 45. • Undrained shear strengths were estimated at 0.1–0.2 MPa under a 2400 m/s compressional wave velocity. [ABSTRACT FROM AUTHOR]

Tensile failure, hybrid failure (combined tension and shear) and shear failure are the three basic failure types of brittle rock. For a long time, little attention has been paid to the first two failure types except for the failure strength of direct/indirect tension, and the deformation characteristics and failure criterion of rock in triaxial extension (herein "triaxial extension" denotes axial tension/unloading-tension in confining pressure P c) are still unclear. This paper proposes a simple auxiliary apparatus to implement triaxial extension tests of cylindrical rock specimens combined with a servo-controlled MTS machine. Subsequently, the mechanics behaviors of sandstone in triaxial extension tests under different constant confining pressures (P c = 0, 5, 10, 15, 20, 30, 40, 50 and 60 MPa) are experimented and analyzed in detail, including the fracture angle, the failure surface morphology, the deformation and strength. With the increase of confining pressure, the failure type of sandstone presents a continuous transition from tensile failure to hybrid failure and to shear failure as a whole. The changes of failure morphology, elastic modulus, Poisson's ratio, maximum strain and failure strength with increase in P c show significant difference among three failure types. For the tested sandstone, the partitions of confining pressure between tensile failure and hybrid failure and between hybrid failure and shear failure are approximately at 20 MPa and 40 MPa, respectively. Hoek-Brown criterion with a tension cut-off and Fairhurst criterion are applicable to fitting the failure strength of triaxial extension test, and the latter presents a satisfying continuous transition from tensile failure to shear failure. [ABSTRACT FROM AUTHOR]

Underground coal mining in the southwestern mountainous area of China causes potential large-scale landslides. To prevent the geohazards of consequent bedding rock slopes after underground mining, the deformation and failure configuration were determined by two landslides caused by underground mining. Then, a prediction model for the fracture failure of the consequent bedding rock slopes was established and validated by physical modeling. The prediction model can analyze the stress and bending moment in the consequent bedding rock slope caused by underground mining and predict the location of fracture failure of the slope. The prediction results for the Masangwan landslide showed that the fracture was at 103.5 m as compared to the actual slip length of 114 m, with an error of 10.5 m, and the relative error at 9.21%. The prediction model has good prediction effect. Physical modeling showed that the crack locations from a similar model appeared at specific intervals in the further advancement of underground mining. The rock mass at a distance from the boundary of the separation zone of the slope surface reached the tensile limit when the length of the separation reached the maximum threshold value, producing tensile cracks. The crack locations from a similar model appeared at specific intervals in the further advancement of underground mining. In addition, the error between the crack location and the prediction result was found to be only 0.0352 m, and the relative error was 5.79%. A comparison between the physical and proposed models showed that the predicted fracture failure is consistent with the laboratory results. The prediction and physical model neglect the impact of environmental factors on fracture development, such as the complex geological structure and the physical and chemical transport of water in the rock mass, resulting in a small error in the prediction results. Therefore, the prediction results can effectively reflect the deformation and failure of consequent bedding rock slopes caused by underground mining. The proposed model can serve as a theoretical basis to predict the geological disasters of consequent bedding rock slopes caused by underground mining. [ABSTRACT FROM AUTHOR]

Highlights • Investigated intermediate strain rate tensile behavior of transparent polyurethane. • Large tensile deformation behavior and tensile failure behavior were analyzed. • Digital Image Correlation technique was adopted to acquire specimen strain. • Strain rate and temperature dependence and their equivalence were observed. • A phenomenological analysis of mechanical quantities was carried out. Abstract Transparent polyurethane has been widely applied in laminated windshield glasses as the interlayer material to enhance the reliability due to its outstanding impact resistance. Under impact loading such as bird strike, the interlayer undergoes large tensile deformation mainly at intermediate strain rates (at the order of magnitudes from 100 to 103, excluding 1000/s). In addition, the interlayer is on service over a wide range of temperatures for a plane traveling around the world. The mechanical behavior of transparent polyurethane under these conditions is not fully understood. In this study, systematical experiments were performed on transparent polyurethane. The viscoelasticity of the material was firstly verified by several quasi-static cyclic tests. Then a series of large tensile deformation and tensile failure experiments were conducted under intermediate strain rates and at temperatures of − 40 ° C to 40 ° C using a servo-hydraulic high-speed tensile machine. All strain data were acquired by the DIC technique. The experimental results show that tensile stress–strain curves and failure behaviors are significantly temperature and strain rate dependent. The rate-temperature equivalence was also observed. Finally, a phenomenological analysis of mechanical quantities of the material was carried out. [ABSTRACT FROM AUTHOR]

The safety assessment of PBX explosive is inseparable from the characterization of its mechanical response and damage. In order to accurately capture the mechanical behavior of PBX explosive, the numerical characterization method of PBX explosive mechanical behavior is studied based on Karagozian& Case (K&C) model framework. The damage evolution mode in the K&C model is modified, and the pressure-dependent characteristics of PBX explosive modulus and damage evolution mode are considered. Based on a series of published experimental data, the strain rate effect in the K&C model was corrected, the ratio of tension to compression meridian of PBX under different pressures was discussed, the deformation localization in the process of structural damage was dealt with, and the treatment of the tensile failure unit in the calculation was presented. The proposed model can be used to well depict the cratering morphology of explosive specimen in the Steven test, and successfully capture the tensile and shear failure images of explosive specimen. [ABSTRACT FROM AUTHOR]

A fundamental study on the tensile failure of rock is conducted using the three-dimensional lattice spring model. The model covers three aspects: (1) the relationship between the mesoscopic tensile/shear failure and the corresponding macroscopic tensile failure; (2) the effects of the size, shape, and location of the initial defect on the macroscopic tensile failure; and (3) the effects of the porosity, heterogeneity, crystal structure, mesoscopic constitutive model, and model scale on its macroscopic tensile responses. Through investigation, this study reveals that the mesoscopic strength heterogeneity affects the macroscopic pre-peak response of rock, and the initial defect could control its macroscopic post-peak response. The post-peak characteristics of the mesoscopic constitutive model influence both the macroscopic pre-peak and post-peak responses, which are scale independent and scale dependent, respectively. Based on these investigations, a parameter-selection method for the mesoscopic constitutive model is established to fully utilize the macroscopic tensile experimental data. [ABSTRACT FROM AUTHOR]

In the two-dimensional simulated reservoir volume (SRV) model, the position of natural fractures is determined only by the approaching angle, and it is only required to consider the influence of horizontal principal stress in its failure criterion. In the three-dimensional shale reservoir, the position of natural fracture needs to be determined by the dip angle and approaching angle while considering the influence of vertical and horizontal principal stress in its failure criterion. In addition, the simultaneous opening of several hydraulic cracks will lead to the change of geostress, thus causing the change of the conditions of the natural fracture and shear failure by the induced tress. In order to analyze the generation of three-dimensional fracture network, this paper establishes a mathematical model based on elastic mechanics, three-dimensional rock failure criterion, full permeability tensor, and material conservation equation. Firstly, the finite element method model of geological stress caused by fracturing is established based on the crack propagation model, and the finite difference method module based on three-dimensional fluid diffusion control equation and full permeability tensor is used to solve the reservoir pressure distribution. Then, the three-dimensional rock tensile and shear failure criteria are used to determine whether any grid units are destroyed. Once a grid has occurred in any form of rock failure criterion, the permeability of the corresponding grid unit will also change due to the change of natural fracture opening. Finally, the stimulated reservoir volume is represented by the region of increased permeability. This paper presents the sensitivity analysis of the multi-factor after using the micro-seismic data to validate the numerical model, including the influence of injected fluid volume, natural fracture approaching Angle, dip Angle and horizontal principal stress difference on the size of SRV (shape, size, border width, length, etc.). Results show that, compared to without the induced stress, the tensile failure volume decreases and the shear failure volume increases, while the total SRV increases due to the induced stress. When the vertical principal stress in the three-principal stress is maximum, the length of the SRV increases with the increase of natural fracture approaching angle, dip angle and horizontal principal stress difference, but its width decreases. Its width and length increase at the same time only with the increase volume of injected fluid; the size of SRV increases with the increase of the injection fluid volume and the natural fracture dip, but decreases with the increase of the natural fracture approaching angle and horizontal principal stress difference. [ABSTRACT FROM AUTHOR]

Abstract Knowledge of the in situ stress state of rock mass is fundamental for engineering, geological and geophysical applications. In situ stress state determination requires in principle the evaluation of the three principal stresses and the related principal directions, but it is widely recognized in the literature that the maximum horizontal stress is the most difficult component to accurately estimate. In the context of borehole methods, this paper proposes a step-by-step analytical procedure to estimate some bounds to the maximum horizontal stress, starting from a geomechanical description of the rock and relying on information generally available in the engineering practice. The procedure is divided in substeps, each one requiring additional information about the mechanical properties of the rock and on the geometrical properties of the failed portion of rock: more information available implies a lower uncertainty on in situ stress estimate. Furthermore, since the proposed procedure is analytical, it allows a complete and very easy implementation in a spreadsheet. The aim of the work is thus to provide a rigourous but simple analytical tool that can be used in engineering practicte to estimate some bounds to the maximum horizontal in situ stress state. The approach is finally validated by means of both numerical simulations, performed with a sophisticated numerical tool, and experimental field data coming from the literature. Highlights • Determination of in situ stress state is crucial for any underground application in many fields of engineering. • Borehole methods have been accepted to be one of the most reliable method to estimate in situ stress state. • A step-by-step analytical procedure is presented to estimate the in-situ stress state relying on drilled borehole information. • Any step of the procedure reduces of the bounds of the maximum horizontal stress, at the cost of more information required. • The procedure is validated by means of both simulations with advanced numerical methods and in situ literature data. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A dynamic spring element model was implemented in a parallel computing framework. • Fibre failure leads to dynamic stress waves. • The dynamic stress waves increase the probability of failure of the fibres. • The dynamic effects are increased when the matrix is considered linear elastic. • The dynamic effects change the cluster formation and material failure. Abstract A spring element model that takes into account the dynamic effects associated with fibre failure in composite materials is presented. The model is implemented in a parallel environment to allow a better performance in the prediction of the complex mechanisms associated with longitudinal tensile failure. The model is used to identify the changes in the stress fields around a broken fibre representing fibre failure as a dynamic phenomenon. In light of these changes in the stress fields, the cluster formation and failure development is analysed and the results are compared with the static spring element model. It is observed that the stress redistribution around a broken fibre is strongly dependent on the dynamic effects and it varies with the material in study, specially if the matrix is considered linear elastic. The changes in local stress redistribution are seen to affect the materials tensile behaviour and cluster formation, being this changes higher for a material with an elastic matrix. [ABSTRACT FROM AUTHOR]

• Responses of jointed rigid pipes under normal faults with various crossings are studied. • Analytical solutions for pipe bending moment and joint shear force at different crossings are proposed. • Excessive joint deflection dominates the pipe safety for relatively shallow burial depth and low soil density. • Increasing the burial depth and soil density, pipe failure mode changes to barrel bending and bell cracking. • Fault-crossing at around 7/10 of the pipe segment is the worst scenario for rigid pipes. The structural safety of jointed rigid pipes can be jeopardized under abrupt ground settlements. Most previous studies have investigated the response and safety of jointed rigid pipes under abrupt ground subsidence using numerical and experimental methods at two specific positions, i.e., the shear band caused by the ground movements crosses the pipe at a joint and at the midspan of a pipe segment. In this work, a closed-form analytical solution for the deformation and mechanical response of jointed rigid pipes under abrupt ground subsidence with various crossing positions is presented. The pipe bending moment and the joint shear force are calculated, which match quite well with the results of finite element analysis. Then the maximum allowable settlements are examined, and the corresponding failure modes are identified. It shows that with the increase of burial depth and soil density, the main failure mode gradually changes from the excessive joint deflection to the barrel bending and bell cracking, and the maximum allowable subsidence distance decreases remarkably. The worst crossing position is at nearly 7/10 of the pipe length. The results offer new insights into the failure mechanism of jointed rigid pipe, and provide a basis for the protection of rigid pipes under abrupt ground subsidence. [ABSTRACT FROM AUTHOR]

In order to theoretically clarify the effect of Cu on Al/Mg 2 Si interface, the calculation method of first principles is employed to determine a stable interface in Al(100)/Mg 2 Si(111) through surface convergence test and adhesion work. This study aims to investigate the stability, electronic structure, and fracture failure of Cu-doped Al(100)/Mg 2 Si(111) interfaces with varying concentrations of Cu. The interfacial bonding strength is the highest when the doping concentration of Cu is 1.85 % according to adhesion work. Comparing with orbital hybridization degree of density of states and pseudogap width of interface total density of states, it can be known that the generation of Mg–Si and Mg–Cu bonds and the best stable Al(100)/Mg 2 Si(111)-1.85 at.%Cu interface, respectively. The difference charge density shows that the charge density between Al–Cu atoms and Mg–Cu atoms is significantly higher than Al–Si atoms and Mg–Si atoms. The average numbers of transfer per atom at the Al(100)/Mg 2 Si(111)-1.85 at.%Cu interface are higher than that at the Cu-undoped Al(100)/Mg 2 Si(111) interface, indicating an increase in ionic bond strength. Tensile simulations of Al(100)/Mg 2 Si(111) and Al(100)/Mg 2 Si(111)-1.85 at.%Cu interfaces were performed. According to tensile stress-strain curve and difference charge density, cracks are initiated in Mg 2 Si due to the fracture of Mg–Si and Mg–Cu bonds. • Cu-doped Al(100)/Mg 2 Si(111) interface models were studied using density functional theory. • From the perspective of adhesion energy and elastic structure, Al(100)/Mg 2 Si(111)-1.85 at.%Cu interface is more suitable. • The tensile strength of Al(100)/Mg 2 Si(111)-1.85 at.%Cu interface is the highest in contrast to Al(100)/Mg 2 Si(111). • The cracks are initiated in Mg 2 Si surface. [ABSTRACT FROM AUTHOR]

In recent decades, numerous geotechnical hazards, including landslides, foundation settlements, and tunnel collapses, have been linked to block-in-matrix rock (bimrock), resulting in substantial damage. The investigation and analysis of the engineering properties and mechanical behavior of both the rock and soil have become increasingly intriguing research areas. However, analyzing bimrock remains a formidable challenge due to its inherent heterogeneity. In this study, to investigate the tensile behavior of the bimrock, the numerical method that couples discontinuous deformation analysis (DDA) and smoothed particle hydrodynamics (SPH) is improved. First, a tension damage model is implemented in SPH for simulating the tensile behavior of the soil. The effectiveness of the presented model is verified through the direct tensile test model and the Brazil disc split model as an indirect tensile test. The contact algorithm of DDA-SPH is then modified by adding a tensile contact spring to introduce tensile strength at the interface between the matrix and the rock in the bimrock. Through a simple pulling numerical model, the accuracy of this modification has been verified, and the appropriate tensile contact stiffness is discussed. Furthermore, using the proposed method, the overall tensile strength of the bimrock with respect to the interface tensile strength is investigated. Finally, the proposed numerical method is applied to the simulation of geoengineering problems, demonstrating the capacity to analyze the stability and large deformation of bimrocks. • A tension damage model is added to the soil-particle based SPH method for simulating the tensile behavior of the matrix. • The contact algorithm of DDA-SPH is then modified by adding a tensile contact spring to introduce tensile strength at the interface. • The overall tensile strength of the bimrock with respect to the interface tensile strength is investigated. • The proposed method is applied to analyzing the bimrock slope and bimrock shallow tunnel. [ABSTRACT FROM AUTHOR]

Abstract Hydraulic fracturing can be considered one of the most effective stimulation methods for fractured network formation. The interaction between induced and natural fractures greatly affects the success of the treatment. In this paper, the extended finite element method (XFEM) and distinct element method (DEM) have been combined to identify the propagation of hydraulic fractures in a porous medium with naturally fractured blocks. DEM is used to investigate hydraulic fractures in a natural-fracture network and evaluate the production flow rate under different apertures and lengths of hydraulic fracture. XFEM is used to simulate the deformation of the natural-fracture interface during the approaching phase of induced fractures as a no-remeshing tool. The results of DEM reveal that length of hydraulic fracturing has a significantly greater effect on production than aperture. Results from XFEM show that tensile and shear debonding of natural fractures change as a function of angle and distance from an induced fracture. Highlights • Hydraulic fracturing in natural fracture reservoirs. • Effective stimulation methods for fractured network formation. • The distinct element method (DEM) and the extended finite element method (XFEM). [ABSTRACT FROM AUTHOR]

Abstract An experimentally validated multiscale computational model for predicting the progressive damage and failure analysis (PDA) of 3D woven textile composites (3DWTCs), is presented. The 3DWTCs are made through a 3D textile weaving process and the dry fiber tows are infused with SC-15 polymer matrix into a single composite material. A thick symmetric configuration of hybridized (carbon, glass and kevlar tows) textile architecture is examined at the entire coupon level to determine the progression of damage under tensile loading and to understand the benefits of hybridization and the resulting performance enhancements. Results also include micro-CT analysis of the laboratory scale coupon to study the effect of microstructure imperfections response. A finite element (FE) model is generated directly from micro-CT data using the software, Simpleware [1]. A three-scale modeling strategy is adopted, where the meso-scale representative volume elements (RVEs) are modeled explicitly in the failure prone gage-area to consider the tow architecture and a 2-layer concentric cylinder (2CYL) [2,3] micromechanics model is used within the fiber tows to consider the fiber/matrix scale and the pre-peak nonlinearity, as caused by matrix microdamage. The analytical subscale model results in a computationally efficient framework for PDA of 3DWTCs. [ABSTRACT FROM AUTHOR]

In a unidirectional composite under static tensile loading, breaking of a fiber is shown to be a locally dynamic process, leading to stress concentrations in the matrix and neighboring fibers and debonding of the interface, which can propagate at high speed over long distances. In our previous work, a fiber break within a two-dimensional fiber array embedded in elastic epoxy matrix (with cohesive interface) was modeled to quantify the effects of these dynamic stresses. The results indicated that the elastic limit of the polymer matrix can be exceeded. In this study, the effects of matrix plasticity on dynamic stress concentrations due to a single fiber break are investigated. For the range of matrix yield stresses considered, the dynamic stress concentrations are significantly higher than corresponding values predicted by a quasi-static model with a pre-broken fiber. Based on the ratio of shear yield strength of the matrix and mode II peak traction of the interface cohesive law, two distinct regimes of damage are shown to exist. Only matrix yielding occurs when this ratio is less than 1.0, while both interfacial debonding and matrix yielding occur when it is greater than 1.0. At higher fiber break strengths, where the elastic matrix model predicts unstable interfacial debonding, reduction in matrix yield strength leads to a transition to stable debonding and arrest. Reducing the matrix yield strength also leads to a lowering of the peak dynamic stress concentrations in adjacent fibers, while spreading the stress concentrations over a larger volume of the composite microstructure. [ABSTRACT FROM AUTHOR]

The dynamic compression responses of four glass spheres with diameters 7.71 mm, 11.90 mm, 17.88 mm, and 24.87 mm are investigated by the modified split Hopkinson pressure bar device (SHPB). Based on the high speed images, the dynamic compression of the spheres can be divided into three stages, e.g. the quasi-elastic deformation stage, the non-linear deformation stage, and the brittle failure stage. The formation and growth of the shadow areas observed at the impact end and the support end in the spheres are the main causes of the catastrophic failure. The movement of the plane-like fronts of the shadow areas is activated and driven by local velocity gradients. Dynamic breakage of the spheres is then analyzed by the particle size distribution, the fractal properties, etc. The results show that there are two main failure mechanisms in the process of sphere breakage, e.g. the tensile failure mechanism and the shear failure mechanism. In order to investigate the transition of these two failure modes, a bimodal Weibull distribution model is preliminarily established on the Weibull statistical strength. The model shows both good simulations to the experimental data and obvious the transition process of two failure mechanisms. The scaling laws and the strain rate effects of breakage strength are then discussed. The results are helpful for the controlling of pulverization for brittle particles. [ABSTRACT FROM AUTHOR]

Horizontal borehole instability raises concern due to negative impacts on success of drilling, reaming and pipe installation during Horizontal Directional Drilling. Shear failure (blow-out) and tensile failure (hydraulic fracture) are the two main failure mechanisms controlling borehole instability in saturated clay. Criteria for categorizing shear failure versus tensile failure are given which are functions of the ratio of undrained shear strength to vertical effective stress S u / σ v ′ and the Lateral Earth Pressure Coefficient at Rest K 0 ′ . Given that S u / σ v ′ and K 0 ′ can be expressed as a function of soil parameters like friction angle, Over Consolidation Ratio (OCR) and Liquidity Index (LI), new forms of these criteria are developed for situations where S u / σ v ′ and K 0 ′ cannot be obtained directly. It is confirmed that tensile failure generally controls in brittle clays like heavily overconsolidated and/or low liquidity index materials. Cases from the laboratory and the field as reported in the literature are used to examine the effectiveness of the new criteria, with inconsistency between theory and the physical evidence explained. [ABSTRACT FROM AUTHOR]

Introduction: This study aims to investigate the strength characteristics of fiber composites under uniaxial tensile stress. Methods: A tensile failure finite element model based on fracture mechanics was built for fiber composites. The principal stress concentration–release–transfer evolution and the crack propagation of the composites under the conditions of equal single fiber width, unequal quantity, and equal total fiber width and unequal quantity were discussed. Results: The tensile strength of the composites increased with fiber quantity when the width of each single fiber was equal. Conclusions: The tensile strength of the composites increased with fiber quantity when the total width of the composite fiber was equal. [ABSTRACT FROM AUTHOR]

Since early 1980s, the oil and gas industry has committed a huge amount of resources towards solving the problem of wellbore instability. Investments in wellbore stability studies are justified by the reduction in drilling and field development costs associated with a stable wellbore. A lot of progress has been made so far. However, wellbore instability continues to present a considerable challenge during well construction operations. The causes of instability and the mechanism of instability especially in shale formations have been studied over the years by several researchers. The results of their experimental and field experiences lead to varying conclusions and differing opinions. This work reviews existing technologies and practices within the industry directed towards understanding the causes of, predicting, preventing, and controlling wellbore instability; highlighting in the process, their limitations and making relevant suggestions. Field examples also provided to buttress some points. [ABSTRACT FROM AUTHOR]