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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]

This study focused on the in-plane rocking behavior of unreinforced masonry (URM) walls. Three URM wall specimens were designed and fabricated based on a typical masonry house in Korea. The experimental parameters were the layout of openings (its presence or absence) and configuration of openings (window or door). Static cyclic loading tests were conducted to investigate nonlinear performance curves of masonry walls subjected to a rocking behavior in the in-plane direction. In this paper, the mortar-joint tensile crack strength and rocking strength of masonry walls (i.e., peak and residual strengths) were evaluated, and the effects of opening configurations on the masonry wall strength were examined, due to the proposed procedure. The deformation capacity of a rocking behavior was also identified by the procedure. As a result, specimens without initial cracks showed the rocking behavior after mortar-joint tensile crack failure, whereas a specimen with initial cracks exhibited only the rocking behavior. Since no remarkable strength deterioration was found until final loading in all specimens, an in-plane rocking URM wall may have very good deformation performance. The estimated mortar-joint tensile crack strength, rocking strength, stiffness, and ultimate deformation were in good agreement with the experimental results, regardless of the layout and configuration of openings.

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]

The tensile fracture is a widespread feature in rock excavation engineering, such as spalling around an opened tunnel. The phase field method (PFD) is a non-local theory to effectively simulate the quasi-brittle fracture of materials, especially for the propagation of a tensile crack. This work is dedicated to study the tensile failure characteristics of rock-like materials by the PFD simulation of the Brazilian test of the intact and fissure disk samples. The numerical results indicate that the tensile strength of the disk sample is anisotropic due to the influence of pre-existing cracks. The peak load decreases at first and then increases with the increase of the inclination angle, following the U-shaped trend. The simulation results also indicate that the wing crack growth is the main failure characteristic. Moreover, the crack propagation path initiates at the tip of the pre-existing crack when the inclination angle is less than 60°. Crack propagation initiates near the tip of the pre-existing crack when the angle is 75°, and it initiates at the middle of the pre-existing crack when the angle is 90°. Finally, all cracks extend to the loading position and approximately parallel to the loading direction. This process is in agreement with the Brazilian test of pre-existing cracks in the laboratory, which can validate the effectiveness of the PFD in simulating the tensile fracture of rock-like materials. This study can provide a reference for the fracture mechanism of the surrounding rock in the underground excavation.

In view of problem of floor heave failure in coal seam roadway, taking 53082 roadway of a mine as the research object, the stress state, displacement distribution and failure form of surrounding rock during the roadway excavation were analyzed and studied by UDEC discrete element simulation software. The results show that under relatively large horizontal tectonic stress, the weak coal seam of roadway floor 53082 becomes the main area of stress release, and the main failure characteristics are shallow tensile failure and deep shear failure. In view of problem that the original support scheme of roadway 53082 can not control the floor displacement and causes serious floor heave, a combined support mode of floor grouting and anchor bolt and cable was put forward through simulation analysis of support effect of different floor support schemes. The test results show that the combined support mode of floor grouting and anchor bolt and cable is superior to the single support mode of anchor bolt and cable, and greatly improves stress state of floor, and restrains the shear failure of deep floor, the displacement of roof and floor is controlled within 150 mm, the displacement of two sides is controlled within 60 mm, and the control effect of surrounding rock of roadway is better.

The mechanisms of dynamic disasters around underground roadways/tunnels were examined by adopting split Hopkinson pressure bar (SHPB) laboratory tests to reproduce the failure process of the surrounding rock subjected to incident stress waves. On the basis of ensuring the consistency of numerical simulations with the experimental results, the failure mechanisms of the surrounding rock and spatiotemporal evolution of the hoop stress around the hole were studied by using a two-dimensional particle flow code (PFC2D). The results of the numerical simulation indicate that tensile stress and compressive stress concentrate along the horizontal and vertical directions around the hole, respectively, owing to the instantaneous incidence of compressive stress waves. The failure modes of surrounding rocks are significantly different when the hole is subjected to various intensities of incident stress waves. In addition, the stability of the surrounding rock of the hole is greatly affected by the amplitude and wavelength of the incident wave and the elastic modulus of the surrounding rock.

The mechanical behavior of loess is highly predicated on variation in its moisture content. While the impacts of the water content on the shearing behavior and collapsibility of loess have been extensively studied, its effect on tensile characteristics has received relatively little attention. In this study, a series of tensile tests were conducted on remolded specimens of a clayey loess that were collected from Ili Valley in China. Two sets of loess specimens with varying water contents were prepared separately using wetting and drying methods. The influence of the water content on the tensile stress–strain response, failure mode and tensile strength was investigated by combining the tensile test results and particle image velocimetry (PIV) analysis. On this basis, a nuclear magnetic resonance (NMR) test and scanning electron microscopy (SEM) observations were implemented in order to assist with the interpretation of the underlying mechanism. The test results indicate that the tensile failure process and the variation of tensile strength with varying water contents differ for specimens that are prepared with wetting and drying methods; a finding which arises from the differences in the soil microstructure, clay–water interaction and the distribution of capillary and adsorbed water. This research has shown that the tensile strength of clayey loess is essentially dominated by the clay’s hydration/cementation and the development of capillary and adsorption suction as well as the microstructural evolution that occurs with the change in the water content. Based on the experimental observations, a conceptual model is proposed in order to interpret the effect of water content on loess’ tensile behavior.

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]

We explored the microstructure-related scale effect on the tensile failure of coal. Disc specimens with different diameters (25 mm, 38 mm, 50 mm, and 75 mm) were processed for the Brazil split test. The influence of microstructures on fracture initiation and propagation was detected and analysed by the combination of X-ray computed tomography scanning, digital image correlation approach, and acoustic emission monitoring. The investigation indicated that tensile strength decreased with increasing specimen diameter, and the relationship can be described by an exponential equation. Four tensile failure modes were observed in specimens with different diameters, namely central, non-central, central edge, and central multiple pattern. Larger specimens exhibited more complicated failure patterns (central edge and central multiple failure patterns) and a greater percentage of shear failure fractures. Strain concentration and strain reversal were observed, respectively, in mineral—inclusion-rich regions and pre-existing discontinuities regions. This possibly contributed to fracture initiation, propagation, and coalescence. Fractures tended to grow along with the interface of mineral inclusion and coal matrix, and they could have propagated into and connect the pre-existing discontinuities. The greater volume of microstructure in larger specimens resulted in fractures that were more complex and may have increased the number of shear failure cracks and led to failure modes that were more complicated. [ABSTRACT FROM AUTHOR]

In this study, a novel shear-lag model based on impregnated fiber bundle (IFB) element is developed to predict the tensile behavior of unidirectional fiber-reinforced polymer (FRP) composites. Rather than using a fiber element, the new model enables a full-field failure simulation due to its finite number of elements. Based on the micromechanical difference equation, we validated the effectiveness of the model and identified the damage evolution pattern by applying it to a basic model of 6 mm FRP tendon. Then, the effect of varied constituent properties, hybrid fibers and initial defects were investigated using the Monte Carlo (MC) method. Several interesting results were found and compared with the findings of earlier studies. For instance, it was found that a more stable IFB strength and higher matrix shear strength reduced variations in composite strength. A moderate hybrid ratio and careful packing of high- and low-elongation fibers helped to achieve optimum composite properties. In the thin-ply composite, transverse initial defects were more detrimental to composite strength than longitudinal defects. These findings prove the value of the bundle-based model, which can be used in future studies as an effective tool for evaluating the strength of various composites.

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]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Copyright of Journal of Central South University is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The umbilical is one of the most important components of a subsea production system. Processing errors and environmental load deviations may occur during the manufacturing process, and the deterministic design based on safety factors is often unable to meet the needs of engineering. In the present paper, the random distribution law of the umbilical geometry parameters is considered to analyse the reliability of the umbilical under the ultimate tensile load by combining the response surface approach of reliability analysis with the finite element analysis. [ABSTRACT FROM AUTHOR]

Although the nonlinear numerical methods to study core discing mechanisms have their merits in terms of linear elastic models, the effects of mechanical parameters and mesh size in numerical simulations still have limits on the accuracy of the results. To address this problem, a parametric sensitivity analysis was conducted to understand the influence of shear and tensile mechanical parameters and mesh size on the numerical results of core discing. Numerical results show that the shear and tensile mechanical parameters have a "cliff effect" on the core discing process. The mechanical responses of the core, the borehole sidewall, and the bottom of the kerf were also contributing to this effect. Next, the simulations using different mesh sizes were conducted to achieve a best fit between the stress-strain curves and the failure modes. Finally, a method was introduced to eliminate the mesh size effects on rock discing in our numerical simulations. [ABSTRACT FROM AUTHOR]

Injection-induced rock mechanical failure risks are critical in CO2 sequestration, and thus there is a need to evaluate these occurrences to ensure safe and reliable subsurface storage. A stress–strain-based numerical simulation can reveal the potential mechanical risks of any CO2 sites. This study investigated the hydromechanical effect on geomechanical failure due to injection-induced stress and pore pressure changes in the prospective CO2 storage site Smeaheia, offshore Norway. An inverted-seismic-property-driven 3D field-scale geomechanical model was carried out in the Smeaheia area to evaluate the rock failure and deformation risks in various pressure-build-up scenarios. A one-way coupling between the before- and after-injection pressure scenarios of nine different models has been iterated using the finite element method. The effect of the sensitivity of total pore volume and pore compressibility on rock mechanical deformation is also evaluated. Although various models illustrated comparative variability on failure potential, no model predicted caprock failure or fracture based on the Mohr–Coulomb failure envelope. Moreover, the lateral mechanical failure variation among different locations indicated the possibility to identify a safer injection point with less chances of leakage. In addition, the pore volume and pore compressibility significantly influence the mechanical behavior of the reservoir and caprock rocks. Although this analysis could predict better injection locations based on geomechanical behavior, a fluid simulation model needs to be simulated for assessing lateral and vertical plume migration before making an injection decision.

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

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]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

It is quite common for fill slopes such as embankments and airport foundations to be constructed in mountainous areas. Steep fill—rock interfaces in such areas undergo tensile failure owing to differences in the stiffness values and tensile strengths of the soil and hard rock. In this study, a new anchor system, termed "radial cable," is proposed to increase the pullout capacity of cables in the fill; this in turn helps control tensile deformation in the fill slope along the interface. In a radial cable, the steel ropes of a conventional cable are equally and symmetrically separated into three sub-cables (a central sub-cable and two branch sub-cables) with a radial distribution starting from the position of the interface. Moreover, each of the sub-cables is fixed in the fill using short U-shaped rigid rods along the cable length and a rigid baffle at its end to further increase pullout resistance. Experimental and numerical uplift tests were conducted to analyze the pullout capacity and anchoring behavior of the radial cables in soil to study the effect of branching. The reinforcement effect of the radial cables was also examined using a case study. [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]

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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]

In order to study the feature extraction and recognition method of fibers' tensile failure, AE technology is used to collect AE signals of fiber bundle's tensile fracture of two kinds of fibers of Aramid 1313 and viscose. A transform called wavelet is used to deal with the signals to reduce noise. A method called Hilbert-Huang transform (HHT) is used to extract characteristic frequencies of the signals after the noise is reduced. And a classification method called Least Squares support vector machines (LSSVM) is used for the classification and recognition of characteristic frequencies of the two kinds of fibers. The results show that wavelet de-noise method can reduce some noise of the signals. Hilbert spectrum can reflect fracture circumstances of the two kinds of fibers in the time dimension to some extent. Characteristic frequencies' extraction can be done from marginal spectrum. The LSSVM can be used for the classification and recognition of characteristic frequencies. The recognition rates of Aramid 1313 and viscose reach 40%, 80% respectively, and the total recognition rate reaches 60%.