Simple Shear Mode Research Articles

Controlling factors of Riedel shear spacing in the simple shear mode of strike-slip fault: Insights from sandbox models

Strike-slip faults generally develop Riedel shears (R-shears), which exhibit parallel and evenly-spaced distribution characteristics. However, the factors controlling the R-shear spacing in strike-slip faults are still unclear. The influence of material properties such as internal friction angle and cohesion, basal friction, and the thickness of brittle layers (T) on the R-shear spacing (S) are investigated using analogue models in this paper. Research findings indicate that the internal friction angle of the material and the thickness of the brittle layer have a significant impact on the R-shear spacing, with the thickness of the brittle layer directly determining the R-shear spacing as evidenced by their linear correlation. In comparison, cohesion and basal friction have insignificant effects on R-shear spacing. Based on this, experiments were carried out using various thicknesses of brittle layers (specified materials) to investigate the impact of the brittle layer thickness on the R-shear spacing, and Particle Image Velocimetry (PIV) is used to analyze the distribution pattern of R-shear development at each stage. The results indicate that fractures occur in regions where the vorticity field alternates between positive and negative values, and as the evolution progresses, the maximum strain gradually converges towards the center of the deformation zone, leading to a reduction in the activity of the R-shear, while the spacing of the R-shear remains unaltered. The normalized (S/T) results indicate that the experimental value of 1.32 aligns with natural laws and is very close to the normalized value of the natural faults, which is 1.24. It can be inferred that the thickness of the seismogenic crust within the range of the Altyn Tagh Fault is 40.9–43.5 km.

Failure zone homogenization at mode II and mixed mode loading including gradient-extended damage and interface debonding at finite strains

Homogenization based on Hills approach is widely used in many scale breaching applications such as the analysis of repeating unit cells (RUCs). However, it was shown that Hills approach is not applicable at the presence of localization phenomena, since in the standard averaging sense the representativeness of the considered micro-scale volume is lost. The failure zone averaging method was shown to overcome these drawbacks and yield converging results even in the softening region. In this paper the failure zone homogenization approach is applied to shear and mixed mode loading of long fiber reinforced plastics. For an accurate description of material failure within the epoxy matrix, a scalar damage model at large strains with gradient enhancement – for mesh size independent results – is used. After a mesh and size convergence study, a statistical analysis of different RUC sizes with random micro structures is performed. Further, the influence of crack closure effects as well as different loading conditions such as simple shear and mixed mode loading are analyzed. It is shown that the implementation of crack closure and application of simple shear lead to different stress–stretch responses. Additionally, crack closure can lead to a different orientation of the failure zone. Finally, an analysis of RUCs with cohesive zone elements for fiber–matrix debonding are shown. Here, lower stresses but higher strains until final failure are observed as well as generally higher dissipation compared to RUCs with perfect interfaces.

Numerical study on liquefaction characteristics of granular materials under Rayleigh-wave strain conditions using 3D DEM

In liquefaction analyses, liquefaction is conventionally assumed to originate from the vertical propagation of shear waves. However, some field and theoretical evidence has demonstrated that the risk of liquefaction may be induced or increased by surface waves. In this study, the liquefaction characteristics of K0-consolidated granular materials under Rayleigh-wave strain conditions, ideal deformation conditions under the assumption of constant volume, were investigated by the three-dimensional discrete element method (3D DEM). The results indicate that Rayleigh-wave strain conditions combine pure and simple shear modes. As the ratio of the shear strain amplitude to the normal strain amplitude (RSN) increases from 1 to +∞, granular materials tend to have a slower liquefaction rate and higher liquefaction resistance; however, the difference in the undrained responses is negligible when the RSN is less than 1. The distribution of the magnitude and orientation of the contact forces also varies with the RSN, while it is similar when the RSN is less than 1. The degradation of the skeleton structure and the evolution of the structural anisotropy accelerate the liquefaction of granular materials. Moreover, in situations with the same accumulated equivalent strain per cycle, the Rayleigh-wave strain condition with a low RSN value will make granular materials more vulnerable to liquefaction compared with Love- and SH-wave strain conditions.

The Influence of Ethyl Branch on Formation of Shish-Kebab Crystals in Bimodal Polyethylene under Shear at Low Temperature

Formation of shish-kebab crystals using a bimodal polyethylene system containing high molecular weight (HMW) component with different ethyl branch contents was investigated. In situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques were used to monitor the formation and evolution of shish-kebab structure sheared at low temperature in simple shear mode and low rate. Only the bimodal PE with no branch formed shish-kebab crystals at the shear temperature of 129 °C, and the shish length increased with the crystallization time, while bimodal PE with branch has no observable shish under the same conditions. The degree of crystallization for bimodal PE with no branch increased with time up to above 7%, while those with ethyl branch increased continually up to above 23%. Furthermore, bimodal PE’s Hermans orientation factor with no branch increased to 0.60, while those with ethyl branch only increased to a value below 0.15. This study indicated that the shish-kebab crystal formed at the low temperature of 129 °C is due to the stretch of entangled chains under shear for the bimodal PE with no branch. Only partly oriented lamellar crystals were formed for the bimodal PE with ethyl branch. All the results at the shear temperatures higher, closed to, and lower than the melting point, the modulation of shish crystals formation owing to different mechanisms of the coil-stretch transition and the stretched network by changing shear temperature was achieved in the bimodal PE samples.

On the Dynamic Soil Behavior under Triaxial and Simple Shear Modes

Abstract Although much has been discussed on the liquefaction phenomenon and cyclic behavior of saturated sands, relatively little has been clarified on the difference between their cyclic behavior...

Circumferential twist in flow forming of tubular parts: Characterization, understanding and control

Circumferential deformation in flow forming of tubular parts affects the axial and circumferential mechanical properties of the deformed workpiece. In this study, by capturing the deflection of weld line in flow forming of welded tube, the characteristic and mechanism of circumferential twist in flow forming are investigated. Simulation and experiment show that the weld line is deflected to a helix with the helix orientation being contrary to that of the helical trajectory of roller on workpiece, which suggests that the circumferential distortion occurs in the form of twist. The circumferential twist is a combination of the shear deformations in θ-z and r-θ planes ( θ -circumferential, r -radial, z -axial). The shear deformation in θ-z plane is nearly the simple shear mode, which is the basis of circumferential twist. The shear strain ε θz is almost equal to the helix angle of the deflected weld line, which is defined as the twist angle for evaluation of the twist degree. The shear deformation in r-θ plane ( ε rθ ) results in a little difference of the circumferential twist distance between the inner and outer surfaces of tube, but makes little difference on the twist angles of two surfaces. Reduction ( ψ t ) and feed rate ( f ) are the first and second significant factors for twist angle, respectively. Twist angle is increased with ψ t and f . A convenient method is proposed to control the circumferential twist by applying a circumferential constraint on workpiece. The tailor-developed flow forming with the applied constraint is more efficient and general than cross flow forming.

Right ventricular myocardial mechanics: Multi-modal deformation, microstructure, modeling, and comparison to the left ventricle

The right ventricular myocardium, much like the rest of the right side of the heart, has been consistently understudied. Presently, little is known about its mechanics, its microstructure, and its constitutive behavior. In this work, we set out to provide the first data on the mechanics of the mature right ventricular myocardium in both simple shear and uniaxial loading and to compare these data to the mechanics of the left ventricular myocardium. To this end, we tested ovine tissue samples of the right and left ventricle under a comprehensive mechanical testing protocol that consisted of six simple shear modes and three tension/compression modes. After mechanical testing, we conducted a histology-based microstructural analysis on each right ventricular sample that yielded high resolution fiber distribution maps across the entire samples. Equipped with this detailed mechanical and histological data, we employed an inverse finite element framework to determine the optimal form and parameters for microstructure-based constitutive models. The results of our study show that right ventricular myocardium is less stiff then the left ventricular myocardium in the fiber direction, but similarly exhibits non-linear, anisotropic, and tension/compression asymmetric behavior with direction-dependent Poynting effect. In addition, we found that right ventricular myocardial fibers change angles transmurally and are dispersed within the sheet plane and normal to it. Through our inverse finite element analysis, we found that the Holzapfel model successfully fits these data, even when selectively informed by rudimentary microstructural information. And, we found that the inclusion of higher-fidelity microstructural data improved the Holzapfel model’s predictive ability. Looking forward, this investigation is a critical step towards understanding the fundamental mechanical behavior of right ventricular myocardium and lays the groundwork for future whole-organ mechanical simulations.

Right Ventricular Myocardial Mechanics: Multi-Modal Deformation, Microstructure, and Modeling

The right ventricular myocardium, much like the rest of the right side of the heart, has been consistently understudied. Presently, little is known about its mechanics, its microstructure, and its constitutive behavior. In this work, we set out to provide the first data on the mechanics of the right ventricular myocardium in both simple shear and uniaxial loading. To this end, we tested ovine tissue samples under a comprehensive mechanical testing protocol that consisted of six simple shear modes and three tension/compression modes. After mechanical testing, we conducted a histology-based microstructural analysis on each sample that yielded high resolution fiber distribution maps across the entire sample thickness. Equipped with this detailed mechanical and histological data, we employed an inverse finite element framework to determine the optimal form and parameters for microstructure-based constitutive models. The results of our study show that right ventricular myocardium exhibits nonlinear, anisotropic, tension/compression asymmetric behavior with negative Poynting effect and minimal hysteresis. In addition, we found that myocardial fibers changes angles transmurally and are dispersed within the fiber-sheet direction. Through our inverse finite element analysis, we found that the Holzapfel model successfully fits these data, even when selectively informed by rudimentary microstructural information. And, we found that the inclusion of higher-fidelity microstructural data improved the Holzapfel model's predictive ability. Looking forward, this investigation is a critical step towards understanding the fundamental mechanical behavior of right ventricular myocardium, and lays the groundwork for future whole-organ mechanical simulations.

Strength and stiffness characterization of clays using Atterberg limits

Atterberg limits are index parameters that can be determined using simple, inexpensive, and rapid laboratory tests. These limits are commonly used for the classifications of fine-grained soils. They may be also utilized in the preliminary assessment of strength and stiffness parameters of these soils, particularly at the initial phases of geotechnical investigation programs, ahead of conducting more advanced tests on undisturbed samples. Numerous studies in the geotechnical literature have been directed towards enhancing the relationships between Atterberg limits and the different mechanical parameters of fine-grained soils. However, there is still a necessity to improve the accuracy and applicability of such correlations. In this study, the undrained rigidity index is correlated with the plasticity indices using a comprehensive worldwide clay database. Subsequently, the effective friction angle is determined using an expression of the rigidity index derived from the Critical State Soil Mechanics. New formulations are developed for the undrained shear strength under compression, extension, and simple direct shear modes, as well as expressions for the constrained, shear, and Young’s elastic moduli. The deduced formulations are validated using the results of the geotechnical investigations for well-reported sites. A close agreement is demonstrated between the measured and the estimated parameters, implying that the proposed approach is broadly valid and applicable.

Large-Scale Combination Direct Shear/Simple Shear Device for Tire-Derived Aggregate

Abstract This paper describes a novel large-scale device capable of performing both direct shear and simple shear tests to evaluate shear deformation and strength properties of Type B tire-derived aggregate (TDA). The device consists of stacked tubular steel members that can be locked as upper and lower rigid sections to displace relative to one another in direct shear or pinned at the ends to translate in simple shear. For both configurations, the TDA specimen has a length of 3,048 mm, a width of 1,220 mm, and an initial height up to 1,830 mm. The upper rigid section of the device can also be used to conduct interface direct shear tests. Vertical stress is applied to the top surface of the specimen using deadweights and horizontal shearing force is applied using two hydraulic actuators in displacement-control mode. Typical results from internal direct shear, concrete interface direct shear, and cyclic simple shear tests are presented. In direct shear mode, the device allows for mobilization of peak shear strength and, in simple shear mode, for evaluation of shear stiffness and damping ratio under large strain conditions for TDA with large particle size.

Equivalent strain at large shear deformation: Theoretical, numerical and finite element analysis

In this study, effective strain is evaluated for large simple/pure shear deformations and new expressions are derived. The validity of these relations was checked by numerical calculations. In addition, finite element analysis of simple shear and pure shear modes of deformation wasconducted using ABAQUS software. Additionally, two other major expressions for evaluating effective strain at large simple shear deformation were investigated and compared with finite element results. Based on FEM results, the linear relation between shear strain and effective strain large strains shall be replaced with the logarithmic one. It is also found that for the same amount of shear strain, a higher value of effective strain is accumulated in the material when it is deformed through simple shear rather than pure shear.

From stretching to mantle exhumation in a triangular backarc basin (Vavilov basin, Tyrrhenian Sea, Western Mediterranean)

In this study, we describe the mode of extension of the Vavilov, a fossil backarc basin, triangle-shaped (approximately 240km-wide and 200km-long), located between Sardinia margin to the west and Campania margin to the east. We combine the analysis of recent geophysical and geological data, in order to investigate the relationship between the crustal/sedimentary structure and the tectonic evolution of both apex and bathyal parts of the basin. With this aim, we interpret a large data set of multichannel seismic reflection profiles and several well logs. We observe that the apex basin corresponds to a sediment-balanced basin, with a sedimentary infill recording the episodes of basin evolution. In contrast, the distal basin corresponds to an underfilled basin, characterized by localized volcanic activity and a thin sedimentary succession that covers the exhumed mantle. The basin architecture reveals the occurrence of rift and supradetachment basins in the Vavilov rift zone. We find that the rifting of the Vavilov triangular basin was synchronous from the apex to distal regions around a single Euler pole located in Latium, between 5.1 and 1.8Ma. The kinematic evolution of the Vavilov basin occurred in two stages: initial pure shear mode (5.1–4.0Ma) that produced high-angle normal faults and syn-sedimentary wedges, followed by simple shear mode (4.0–1.8Ma) that caused supradetachment basins filled by a Transgressive-Regressive succession that documents high subsidence rates (1.22mm/y) in the apex region. The final stage of extension in the distal region led to: (i) complete embrittlement of the crust; (ii) direct continuation of crustal faults to upper mantle depth; (iii) serpentinization and mantle exhumation. Based on constraints on the present-day crustal structure of the Vavilov basin, we obtain a stretching value (β=3.5) and extension rates (3cm/y) in the bathyal zone analogous to those reported for magma-poor rifted margins.

Fault systems at hyper-extended rifted margins and embryonic oceanic crust: Structural style, evolution and relation to magma

The study of seismic sections derived from the magma-poor Australia-Antarctica rifted margins enables to investigate the structural style and evolution of fault systems and their relation to magmatic additions during final rifting and lithospheric breakup. The aim of this study is thus to better characterize fault systems, their organization in time and space as well as their relationship to magmatic systems. Our observations show that extensional detachment faults related to mantle exhumation form out-of-sequence, and initiate as normal upward concave faults. The observations can be best explained by an alternation between a pure shear mode (development of symmetric arrays of normal faults) and a simple shear mode (development of detachment faults), with a continuous delocalization and re-localization of the deformation in the footwall of the previous exhumation fault. This model suggests that the asthenospheric uplift is slow and decoupled from the deformation in the brittle and serpentinized upper basement layer. The presence of such a décollement level, possibly formed by the serpentinisation front, has a major control on the style and organization of faulting. The polyphase, out-of-sequence organization of faults can explain that despite mantle exhumation is accommodated along multiple asymmetric exhumation faults, the overall exhumed mantle domain is mostly symmetric at the scale of both margins.

Effect of Surface Roughness on the Stick-slip Behavior of Magnetic Field Controlled-dipolar Suspensions in Simple Linear Shear Mode

The effect of surface roughness on the stick-slip motion of Magnetorheological (MR) fluids under a simple linear shear mode has been experimentally reported. The shear stress of the MR fluids could be modulated by the changing of the surface roughness. The rate of energy accumulation and releasing during stick-slip motion changed with respect to the shear plates of different surface roughness. The changing of the stick-slip motion based on the different surface roughness was ascribed to the evolution of internal particle structures when shear motion was applied to the aggregates of the particles exposed to the external magnetic field.

Stick-slip behavior of magnetorheological fluids in simple linear shearing mode

The stick-slip motion of magnetorheological (MR) fluids under a simple linear shear mode has been experimentally reported. The critical shear strain for the onset of the stick-slip motion decreases logarithmically with the magnetic flux intensity applied. The rate of energy accumulation and releasing during stick-slip motion changed in a power law of the viscosity of the continuous phase in a range of 0.01~1000 mPa S. Different carrier fluids led to different stick-slip characteristics. The stick-slip motion can be fully suppressed with certain carrier fluids. When the MR fluids are in a shear-thickening state, the critical shear strain of the onset of the stick-slip motion is larger than a normal state. But, the relative spike amplitude of the stick-slip remains similar.

Mechanism Analysis on Vertical Gradation of Rock Avalanches Triggered by Wenchuan Earthquake, Sichuan, China

Study on rock avalanche kinematics is still a hotspot in the world, especially after the Wenchuan earthquake. To examine this mechanism further, some rock avalanches triggered by the Wenchuan earthquake are taken as objects in this paper. After a detailed field investigation of the vertical profiles revealed by natural longitudinal trenches formed in the rock avalanche deposits, an obvious vertical gradation along their sliding paths is observed, and proposed to be divided into five zones from the top to the bottom and named as follows: the air-blast zone, the bouncing and jumping zone, the sliding and deposit zone, the basal travel zone, and the original accumulation zone. Based on the characteristics of these zones, the formation of each zone is discussed in detail with corresponding conclusions proposed: (1) The air-blast zone, as the upper boundary of the area damaged by rock avalanches, is destroyed by wind gusts initiated by a large rapidly moving mass. (2) The bouncing and jumping zone, mainly characterized by the display of accumulated fine grains and isolated blocks, is produced by the co-work of escaping force of entrapped air and debris internal force. (3) The coupling effect of kinematic sieving and momentum transfer is the main reason for the formation of sliding and deposit zone. (4) Debris in basal travel zone goes through a complex dynamical process: collision, dilation, fragmentation, rotation and sliding, and compaction. In this process, both the overburden pressure and the self-excited vibration energized by the undulated slip surface are the main dynamical forces controlling the formation of basal travel zone. And the simple shear and pure shear modes are the main mechanical behaviors, which realize the formation of particle fragmentation, a binary mixture with coarse particles embedded in clay matrix, and alignment distribution of particles in basal travel zone.

Stress Dependence of Shear Strength in Fine-Grained Soils and Correlations with Liquid Limit

The undrained strengths and friction angles of a variety of natural fine-grained soils are investigated over an effective stress range of 0.1 to 10 MPa. The resedimentation technique was used to produce identical saturated samples for laboratory shear testing. The majority of the results presented are derived from Ko-consolidated undrained triaxial compression tests, although behavior under direct simple shear and triaxial extension modes of shear is also presented for a single soil. Normalized shear stress-strain responses, undrained strength ratios, and critical state friction angles are found to vary considerably and consistently at each overconsolidation ratio when viewed over a significant effective stress range. Correlations are developed that allow the undrained strength and friction angle of a fine-grained soil, as well as the variation in these properties with stress level, to be estimated effectively from liquid limit, together with an evaluation of the in situ stress history of the sediment. Liquid limit is an easily measured index property that reflects the clay mineralogy and clay fraction of a soil.

Discussion: Laboratory measurement of strength mobilisation in kaolin: link to stress history

CONTRIBUTION BY P. W. MAYNE While Vardanega et al. (2012) present an interesting empirical power law relationship for representing the stress– strain response of clays under constant volume, they must take care in the mixing and matching of different strength modes. In particular, the observed increase of normally consolidated undrained shear strength ratio (cu=s’v0)nc with plasticity index (Ip) given by equation (4) was specifically developed on the basis of raw (uncorrected) vane shear strengths measured in the field on natural clays. The general trend for the shear strength ratio from field vane tests (FVTs) varying with Ip is reported by Bjerrum (1972), Larsson (1980), Jamiolkowski et al. (1985), Chandler (1988) and Leroueil & Hight (2003), albeit using non-linear relationships such as power law rather than the original linear form. On the other hand, the general trend for the strength ratio (cu=s’v0)nc from triaxial compression (TC) tests on clays shows essentially no dependence on Ip (Larsson, 1980; Jamiolkowski et al., 1985; Ladd, 1991; Ladd & DeGroot, 2003). As a consequence, this fact led Chandler (1988) to recommend an Ip expression that inter-relates FVT strengths to equivalent TC values. Figure 9 shows the trends of (cu=s’v0)nc versus Ip using the original FVT dataset of Skempton (1957) and the laboratory dataset from TC, direct simple shear and triaxial extension modes presented by Ladd & DeGroot (2003). While the FVT data show a strong correlation with Ip (r 2 5 0?946), the TC data do not (r 5 0?0002). These trends have been supported by larger datasets including over 200 vane shear test (VST) data and over 200 laboratory strength data (Mayne, 2012). On the other hand, as per the theoretical link established by critical state soil mechanics, the ratio (cu=s’v0)nc for TC mode increases with the effective stress friction angle w9 of the clay, as verified elsewhere (Mayne, 1988, 2012).

NGI‐ADP: Anisotropic shear strength model for clay

SUMMARYMany geotechnical problems involve undrained behavior of clay and the capacity in undrained loading. Most constitutive models used today are effective stress based and only indirectly obtain values for the undrained shear strength. To match the design profiles of undrained shear strengths, in active (A), direct simple shear (D) and passive (P) modes of loading are complicated. This paper presents the elastoplastic constitutive model NGI‐ADP which is based on the undrained shear strength approach with direct input of shear strengths. Consequently, exact match with design undrained shear strengths profiles is obtained and the well‐known anisotropy of undrained shear strength and stiffness is accounted for in the constitutive model. A non‐linear stress path‐dependent hardening relationship is used, defined from direct input of failure strains in the three directions of shearing represented by triaxial compression, direct simple shear and triaxial extension. With its clear input parameters the model has significant advantages for design analysis of undrained problems. The constitutive model is implemented, into finite element codes, with an implicit integration scheme. Its performance is demonstrated by a finite element analysis of a bearing capacity problem. Copyright © 2011 John Wiley & Sons, Ltd.

Rheology and flow behavior of suspensions of nanosized plate‐like particles in polyester resins at the startup of shear flows; Experimental and modeling

AbstractApplications of organoclays to polymer resins are potentially of great technical interest. This research targets preparation and characterization of nanocomposites of organoclays in an unsaturated polyester resin (UP). The nanocomposites with two distinct dispersion levels were compounded in a complex multisteps mixing process at three concentrations and subsequently their microstructures were characterized by XRD. The solution‐state rheological properties of layered silicate/UP were measured in the start‐up of steady state in the simple shear mode and analyzed based on our observations of internal structure of nanoparticles dispersion. Strong shear thinning behavior caused by increasing particle alignment induced by the shear field was observed for the suspensions. Effects of nanoparticles loadings and shearing on transient viscosity of the UP resin were examined. The experimental results show that increasing shear time in nanosuspension preparation steps and hence improvements of nanoplate dispersion in the polyester resin give rise to viscosity of the suspensions. A theoretical analysis of the motion of rigid ellipsoidal particles in a Newtonian fluid based on the thermodynamic approach and Jeffery's analysis of the motion of ellipsoid particles with an interaction term was developed to determine the orientation state of disc‐shape layers and then, the expression for the extra stress tensor was calculated to predict transient viscosity and normal stress differences. It is found that the thin oblate particles have significant orientation preference in the shearing direction. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers