Development Of Shear Bands Research Articles

A particle-scale investigation of mechanical behavior of cemented hydrate-bearing sediment using Discrete Element Method

Natural gas hydrate (NGH) is a promising clean energy with the characteristics of high density and considerable reserves. To avoid geo-hazards induced by the exploitation of gas hydrates, it is essential to study the mechanical properties of hydrate-bearing sediments (HBS). Because the hydrate cementation has a great influence on the mechanical behavior of HBS, this paper aims to study the mechanical behavior of cemented HBS by using the discrete element method (DEM) and reveal the cementation effect on mechanical properties by comparing the simulation results obtained by two cementation patterns. A series of numerical biaxial compression tests under different confining pressure are carried out on HBS specimens with various hydrate saturation. The stress–strain curves, strength, and stiffness of numerical specimens are obtained by simulation tests. The results show the cementation effect contributes to improving the strength and stiffness of HBS but the presence of hydrates mainly enhances stiffness. In addition, the mechanical behavior of HBS is investigated at the particle scale. For example, the increasing confining pressure and hydrate cementation can limit the slip and rearrangement of sand particles, which induce the strengthened strength of HBS. The shear band formation and development are related to cementation failure.

A Study on the Law of Ring-Shear Band Evolution

A separate-bottom Couette cell is used to carry out ring-shear tests on sand and hydrate, and the evolution of shear bands is recognized using the tracer method. Based on experimental verification, a numerical simulation method is applied to study the shear band variation law with the height and strength of the sample. Analyzing the distribution of stress and strain gives a dimensionless number (c+ρgH·tgφ)H/αGL that affects the characteristics of the shear band, which indicates that the evolution direction and form of the shear band are controlled by the stiffness ratio of strength to load. Furthermore, the dimensionless law of the height and width of the shear band is given quantitatively.

Lateral Earth Pressure Distribution and Shear Band Development within Back-to-Back Mechanically Stabilized Earth Walls Under Seismic Conditions

Lateral Earth Pressure Distribution and Shear Band Development within Back-to-Back Mechanically Stabilized Earth Walls Under Seismic Conditions

Microstructural evolution and reverse flow in shear-banding of entangled polymer melts.

The temporal and spatial evolution of shear banding under startup of shear flow was simulated for highly entangled, linear, monodisperse polyethylene melts of differing molecular weight, C750H1502, C1200H2402, and C3000H6002, using a high-fidelity coarse-grained dissipative particle dynamics method. It was determined that shear stress was dominated by segmental orientation of entangled strands at low shear rates, but at a critical shear rate below the reciprocal of the Rouse time, flow-induced disentanglement resulted in the onset of chain tumbling that reduced the average degree of orientation, leading to a regime of decreasing shear stress, with a commensurate onset of increasing average chain extension imposed by the strong flow kinematics that ultimately drove the steady-state shear stress higher. During startup of shear flow, shear band development began immediately after the maximum in the first normal stress difference, where distinct fast and slow bands formed. The slow bands consisted of relatively entangled and coiled molecules, whereas the fast bands consisted of more disentangled and extended chains that experienced quasiperiodic rotation/retraction cycles. The simulation results often exhibited a generation of temporary reverse flow, in which the local fluid velocity was temporarily opposite to that of the bulk flow direction, at the onset of the shear-banding phenomena; this effect was consistent with earlier experiments and theoretical results. The physical mechanism for the generation of reverse flow during shear-band formation was investigated and found to be related to the recoil of the molecules comprising the slow band. Overall, the phenomenon of shear banding appeared to arise due to flow-induced disentanglement from orientational ordering and segmental stretching that affected individual chains to different degrees, ultimately resulting in regions of relatively coiled and entangled chains that evolved into a slow band, whereas the locally disentangled chains, experiencing quasiperiodic stretch-rotation cycles, formed a fast band. The transitional period resulted in a kinematic instability that generated the temporary reverse-flow phenomenon.

Development of irreversible deformation and localized shear bands under horizontal compression of the sedimentary layer

Within the framework of the elastoplastic model, the development of irreversible deformation during horizontal compression of a sedimentary layer lying on a rigid foundation is considered. The influence of strength parameters of the medium and friction in the base on the configuration of plasticity zones and localization of deformation has been studied. Analytical estimates are made of the depths at which irreversible deformation develops, as well as their changes as a result of an increase in horizontal stresses. With the help of numerical simulation, the features of the origin and development of localized shear bands are shown. Schemes are constructed illustrating the nature of the development of localization bands depending on the properties of the medium.

Intense shear band plasticity in metallic glass as revealed by a diametral compression test

Shear band initiation, development and mutual interaction are studied in a Zr55Cu30Al10Ni5 metallic glass by means of an innovative experimental technique associating diametral compression test (or Brazilian test), scanning electron microscopy and digital image correlation analysis. The intense strain occurring in shear bands and the deformation map of their overall pattern are both estimated with a high resolution (∼5μm/pixel), offering a better understanding of the phenomenon. Finite element simulations based on a new and original plasticity model, the compartmentalized model, makes it possible to reproduce the shear band development observed experimentally, as well as the interlocking mechanism occurring between the shear bands.

Strain partitioning in a dual-phase steel under plane strain compression

Modern design of steels with improved mechanical properties is often based on multiphase microstructures such as in dual-phase steels. The tailoring of these alloys requires a thorough understanding of strain partitioning and the correlation of strain related phenomena in different scales and under different loading paths. These questions are usually addressed by means of empirical techniques and numerical simulations using representative volume elements (RVE). The assessed loading conditions are most often simple shear, uniaxial tension, and hole expansion and these studies mainly focus on microstructural damage progression under low strains. This study aims to develop a coupled experimental-numerical approach to examine the fractal nature of strain partitioning in a dual-phase steel (DP600) under plane strain compression. This deformation path allows the achievement of significantly higher strains up to the extension of possibly promoting grain fragmentation within highly deformed shear bands. From a fractal perspective, it is demonstrated the development of micro-scaled shear bands due to microstructural heterogeneities within macro-shear bands characteristic of plane strain compression. Additionally, the results obtained from the 2D-RVE model were critically examined and compared with several experiments at different scales to provide further understanding on the limitations and capabilities of the approach.

Microstructure evolution of adiabatic shear band in AZ31 alloy under dynamic compression

The formation of adiabatic shear band (ASB) and its damage behaviour in AZ31 alloy under high strain rate compression (2000 s−1) were investigated in this study by using a split Hopkinson pressure bar. Microstructure of the ASB was characterised by electron back-scattering diffraction and transmission electron microscopy, and the adiabatic shear damage behaviour was analysed through finite element simulation by LS-DYNA. The results show that the ASB and the surrounding microstructure form a gradient microstructure distribution, and the formation of ultra-fine grains in the ASB is due to rotational dynamic recrystallisation. The combination of work hardening and grain refinement in ASB leads to a high microhardness. Micro-voids grow in the ASB and eventually form macro-cracks, leading to material failure.

Evolution of cracks in the shear bands of granite residual soil

The evolution of shear bands and cracks plays an important role in landslides. However, there is no systematic method for classification of the cracks, which can be used to analyze the evolution of cracks in shear bands. In this study, X-ray computed tomography (CT) is used to observe the behavior of granite residual soil during a triaxial shear process. Based on the digital volume correlation (DVC) method, a crack classification method is established according to the connectivity characteristics of cracks before and after loading. Cracks are then divided into six classes: obsolete, brand-new, isolated, split, combined, and compound. With evolution of the shear bands, a large number of brand-new cracks accelerate the damages of materials at the mesoscale, resulting in a sharp decrease in strength. The volume of brand-new cracks increases rapidly with increasing axial strain, and their volume is greater than 50% when the strain reaches 12%, while the volume of compound cracks decreases from 54% to 21%. As cracks are the weakest areas in a material, brand-new cracks accelerate the development of shear bands. Finally, the coupling effect of shear bands and cracks destroys the soil strength.

X-ray-aided characterization of micro-hydro-mechanical behaviour of unsaturated sand using a suction-controlled mini-triaxial system

Despite the advancement of the knowledge of unsaturated soil behaviour developed over the past decades, the understandings remain largely at the macro or element scale. Existing testing systems allow simultaneous in situ loading and X-ray imaging to facilitate the studies at micro or pore scale, but the soils of concern are normally two-phase (i.e., dry or saturated). This paper develops a new suction-controlled miniature triaxial apparatus for studying the micro-hydro-mechanical behaviour of three-phase unsaturated soils via in situ quantification of the evolutions of soil microstructures, aided by micro-X-ray computer tomography imaging. The apparatus can independently control combinations of net mean stress and matric suction whilst permitting high-resolution full-field imaging of the entire samples through the image analysis via methods of pore network modelling and discrete digital image correction. Results reveal that at equilibrium, suction at the “transition zone” of the soil does not necessarily mean to have both the air and water phases continuous, as otherwise recognized at the element scale. This phenomenon leads to nonuniform distributions of local void ratio and degree of saturation. Post-peak strain localization and shear band development are explained by the movements of pore fluid and the associated influences on local soil void ratio change.

Effects of processing routes on recrystallization texture development and magnetic properties of 0.10 mm ultrathin non-oriented electrical steel sheets for high-frequency application

Fabricating ultrathin non-oriented electrical steels (NOES) sheets has been a challenge because the severe plastic deformation inevitably results in undesirable texture such as intensive γ-fiber (<111>//ND). In the present work, both one-stage rolling route with severe plastic deformation and two-stage rolling route combining different rolling process and the intermediate annealing were used to prepare 0.10 mm-thick 3.1Si-0.8Al NOES. A rare phenomenon was found that severe plastic deformation in one-stage rolling route split the orientations of α (<110>//RD) grains through deformation banding and caused lattice curvature, exhibiting the similar microstructure characteristic and stored energy distribution as the deformed γ-grains. As a result, dominant α*-fiber ({1 1 h} <1 2 1/h>) and relatively soft α-fiber textures besides sharp γ-fiber recrystallization texture were formed, which seriously deteriorated the magnetic induction and led to high magnetic anisotropy. By comparison, the two-stage rolling route favored the development of shear bands and increased the final grain size. As the second rolling reduction decreased, detrimental γ- and α*‐fiber recrystallization textures were significantly weakened, whereas λ-fiber (<001>//ND) and {117}<291> recrystallization textures were enhanced. Besides, the final grain size was gradually increased. Therefore, the magnetic induction was continuously improved and the core loss was gradually decreased. Another new finding was that magnetic anisotropy was simultaneously improved as a result of the occurrence of {117}<291> texture and the weakening of α*-fiber texture. The recrystallization mechanism of specific texture components was investigated in detail.

Study of Dynamic Evolution of the Shear Band in Triaxial Soil Samples Using Photogrammetry Technology

In order to avoid the influence of end restraint on triaxial stress and strain measurements, this study combines photogrammetry and computer technology to apply to the unconsolidated undrained test of triaxial soil samples. The novel method can establish an intuitive shear band evolution model of soil samples and help attain a clear and intuitive shear band evolution law. On the basis of the conventional triaxial test, this new method needs to paste the RAD (Ringed Automatically Detected) code points on the rubber film, plexiglass cover and brackets and then take pictures of the RAD code points in the loading process in a surrounding manner, with which the 3D shape of the restored soil samples can be determined. After eliminating the influence of refraction, the coded point cloud coordinates measured in the experiment can be used to calculate the axial deformation and radial deformation of the soil sample in the deformation process and determine the local stress–strain curve and three-dimensional displacement field diagram of the soil sample. The test shows that the new method can clearly determine the peak value and inflection point of the stress–strain curve in the middle region of soil samples, enabling it to reflect the shear change process of the soil sample more accurately. In addition, the displacement field can be used to directly observe the formation, development and penetration process of the shear band in soil samples.

Dynamic behavior of geocell-reinforced rubber sand mixtures under cyclic simple shear loading

Due to the attributes of low shear modulus and high initial damping, rubber sand mixtures (RSM) can be used as a soil alternative to reduce ground motions when seismic loads are of great concern. However, when RSM is used as a vibration isolation material for geotechnical seismic isolation systems, it suffers from a lack of load-bearing capacity. To overcome this, a three-dimensional interconnected geocell (one type of geosynthetics) is placed within RSM to increase the vertical confinement of the system. In this technical note, to investigate the shear modulus and damping ratio of geocell-reinforced RSM, large-scale cyclic triaxial tests were conducted on specimens prepared with four granulated rubber contents (by weight) and sheared under different cyclic shear strain amplitudes. The results show that Geocell reinforcement can restrict the development of local shear bands in the specimen, weaken the anti-S-shaped characteristics of hysteresis loops and enhance the damping ratio of RSM at large strain amplitudes. The tuck net effect causes an increase in the normal stress of both contact particles, and then leads to the degradation rate of the maximum shear modulus of RSM varying with the rubber content and vertical pressure. The normalized shear modulus degradation curves show the influence range of geocell reinforcement, and demonstrate that a rubber content of 20% for reinforced specimen may be an optimal value from the perspective of the stability of dynamic properties. Additionally, the quantitative analysis of the effect of geocell reinforcement on the mechanical behavior of RSM can provide a reference for subsequent theoretical research and engineering applications.

Investigation of the shear band evolution in soil-rock mixture using the assumed enhanced strain method with the meshes of improved numerical manifold method

Falling into the framework of the Petrov-Galerkin finite element formulation with embedded discontinuity, the assumed enhanced strain (AES) method could simulate the structural localization phenomenon and the associated loss of bearing capacity in a way insensitive to mesh alignment and refinement. For another hand, the improved numerical manifold method (INMM) naturally excels at dealing with heterogeneous problems such as the soil-rock mixture (SRM) slope with embedded soft soil region. Therefore, to simulate the shear band evolution in heterogeneous slope more efficiently, precisely and also mesh independently, this paper proposes to invoke the AES method with the meshes of the INMM. Beside, this paper proposes a simple and efficient method to address the constitutive integration for multi-surface plasticity induced by cutting the tensile part of the Drucker Prager model. Finally, the efficiency and accuracy of the proposed approaches are tested on some typical examples including heterogeneous block and slope.

Formation of η-oriented shear bands and its significant impact on recrystallization texture in strip-cast electrical steel

The evolution of shear band (SB) and texture in strip-cast electrical steel was studied in order to investigate the crystallographic character of SB and its influence on recrystallization texture. Shear deformation in the form of SB played an effective role in tailoring the local lattice rotation to accommodate heavy deformation in the case of inhomogeneous deformation under conditions of initial coarse grain in strip-cast electrical steel. During rolling process, η-oriented SBs appeared at different stages of deformation as a result of geometric softening. Cube-oriented SB was mainly retained from initial exact Cube grain at early stage of shear deformation and Goss-oriented SB was newly developed during the formation of γ-fiber matrix after heavy deformation. {210}<001> SB formed as a transition form among different SBs. Crystal rotation inside SB, SB dimension and SB boundary misorientation progressed in proportion to cold rolling reduction. It is demonstrated that crystallographic direction of SBs tended to be parallel to <001> under the driving force of reduction in stored energy to maintain relatively quasi-stable state. Low orientation gradient as well as relatively low density of dislocations was developed within SB region, while high orientation gradient formed between SB region and surrounding matrix. Interestingly, the η-oriented cell blocks inside SBs provided preferential nucleation sites for Goss and Cube texture at early stage of recrystallization, which significantly contributed to beneficial recrystallization texture in a manner of texture inheritance and superior magnetic properties (B50 was as high as 1.81 T, and P1.5/50 was as low as 4.0 W/kg).

Mechanical size effect and serrated flow of various Zr-based bulk metallic glasses

Despite superior mechanical properties, the cross-scale mechanical properties of Zr-based bulk metallic glasses (BMGs) are urgent to be revealed. Depth-sensitive nanoindentation technique was employed to directly investigate the significant depth-dependent mechanical properties of three kinds of Zr-based BMGs. Specifically, the surface hardness H and elastic modulus E are verified to increase with the decrease of indentation depth while the fracture toughness KIC decreases with the indentation depth. The mechanical size effect is closely related to the evolution of shear bands at various indentation depths, which can be equivalently revealed by the distribution of serrated flow. Based on a relatively shallow indentation depth, the comparatively minor stress gradient established inside the micro-region underneath the indenter tip induces insufficient activation energy of shear bands, which prevents the nucleation of shear bands and further restricts plastic deformation, and ultimately results in enhanced surface hardness and elastic modulus but reduced fracture toughness. In addition, the shear band morphology of residual indentation and the stress distribution obtained from the finite element simulation provide integral evidence in support of the depth-induced mechanical size effect.

The evolution of adiabatic shear band in high Co–Ni steel during high strain-rate compression

The microstructural evolution and formation mechanism of adiabatic shear band (ASB) in M54 steel were investigated using split Hopkinson pressure bar (SHPB). Specially, the strain response to ASB was analyzed systematically by strain controlling dynamic compression tests at high strain-rates. The results demonstrated that the ASBs started to form at 23% strain and shearing failure strain was increased to 28% at strain-rate of 4000 s−1. The ASBs in the M54 steel was consist of a transformed adiabatic shear bands (T-ASB) and deformed adiabatic shear bands (D-ASB). The evolution of the ASBs was revealed and the generation of fine equiaxed nano-grains within ASBs was attributed to the rotational dynamic recrystallization mechanism. The twinning process was actually the reverse transformation of ω→bcc and the driving force was the lattice instability of martensite matrix caused by carbon redistribution.

Shear band propagation and mechanical behaviours of landslides under top loading

The configuration of slip surface is conventionally regarded as a key characteristic to distinguish slope failure modes that are embedded in the limited equilibrium method and the bearing capacity theories. However, few studies indicated that a different way of propagating a slip surface with the same configuration might affect the mechanical behaviour and failure mode of the slope. In this paper, the mechanical behaviour is studied in two slopes that have a similar configuration of slip surface with different processes of shear band evolution. Advances in transparent soil technology allow the non-intrusive observation of shear band development in the laboratory slope models. This paper presents shear band development inside slopes using the transparent soil technique and then analyse the mechanical behaviour via the discrete element method (DEM). In order to reproduce the laboratory results, the real shape of transparent soil particles is used in the DEM model, and the microscopic parameters are calibrated by response surface methodology (RSM). The mechanical parameters such as movement, stress, void ratio and energy dissipation are measured in different stages of shear band evolution and are measured in four regions: the weak plane, the shear band, the slope mass above the slip surface, and the slope mass below the slip surface. This paper presents the role of shear band propagation in the mechanical behaviour of slope and discusses the possibility of monitoring the mechanical behaviour of slope to predict the coalescence of slip surface.

High frequency cutting force measurement during saw tooth chip formation of Al-7075-T6 for critical flow stress estimation

Shear banding is an unstable mode of deformation caused by material beginning to soften or weaken with additional strain, resulting in narrow bands of highly deformed material called shear bands. Shear bands occur in metal cutting when deforming material in the primary shear zone is subject to weakening by ductile damage and/or thermal softening by adiabatic heating. Recent work [1] has shown that the force supported by shear bands induced in hat-shaped test specimens subject to high-speed compression can be measured during the evolution of shear bands. This has given rise to the question whether very high band-width force measurement can be used to quantitatively measure the strain softening of material during high-speed machining. The challenge impeding measurement of cyclic changes in cutting and thrust force during shear banding cycles in orthogonal cutting is the rate at which these shear bands typically occur – from a few kHz to 100 kHz. This is well above the lowest natural frequency of even stiff cutting force dynamometer setups. This paper describes the development and validation of a high bandwidth dynamometer. This is used to measure both the cutting and thrust forces during orthogonal cutting of AA 7075-T6 with unprecedented fidelity. The critical flow stress at which flow softening initiates is calculated from the measured forces and chip morphology.

Shear band development under simple shear and the intrinsicality of strain softening of amorphous glassy polymers

The development of shear bands that induced by localized strain inhomogeneity is a characteristic deformation mechanism and determines ductility of amorphous glassy polymers. To investigate the essence of intrinsic strain softening and its influence on shear band evolution under shearing and reverse shearing, a full-network constitutive model based on the micro-mechanism is implemented into the material point method and finite element method respectively. The results show that the shear band nucleates and propagates in forward shearing, and gradually fades until disappears in following reverse shearing when the specimen regains its original geometry. As reverse shearing proceeds or there is a second forward shearing, the homogeneous plastic deformation occurs preferentially in the previously deformed band but it doesn't display any shear band like the initial forward shearing. It means the glassy polymers undergoing plastic deformation cannot be recovered by reverse straining. In further shearing, new shear bands tend to be initiated outside the existing band and then propagates to merge with the previous band. The initiation and propagation of shear band along the shearing direction is caused by the intrinsic strain softening, independent of loading histories and boundary conditions. The widening of shear band is related to the strain hardening. • Origin of intrinsic strain softening lies in the saturation of plastic shear strain. • Amount of intrinsic strain softening keeps fixed. • Glassy polymers undergoing plasticity cannot be recovered by reverse straining. • Full-network model can capture the shear band evolution under reverse shearing.