Anisotropic time-dependent behaviors of shale under direct shearing and associated empirical creep models

Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue.In this context,we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e.0°,30°,45°,60°,and 90°),under multiple levels of direct shearing for the first time.The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior.Under a low shear stress,the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations,and the increase depends on the bedding orientation and creep time.Under high shear stress conditions,the creep compliance of shale is minimal when the bedding orientation is 0°,and the steady-creep rate of shale increases significantly with increasing bedding orientations of 30°,45°,60°,and 90°.The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation.A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed.The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate.The applicability of the five classical empirical creep models is quantitatively evaluated.It shows that the logarithmic model can well explain the experimental creep strain and creep rate,and it can accurately predict long-term shear creep deformation.Based on an improved logarithmic model,the variations in creep parameters with shear stress and bedding orientations are discussed.With abovementioned findings,a mathematical method for constructing an anisotropic shear creep model of shale is proposed,which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation.

Experimental investigation on the factors affecting VWF damage based on an in vitro blood-shearing platform

With the increasing number of people suffering from heart failure,ventricular assist devices have gradually become an effective way to treat end-stage heart failure.However,the blood damage caused by ventricular assist devices has not been effectively solved,which is an obstacle to its clinical promotion.Most research focused on erythrocyte damage under shear stress,while few researches were conducted on the interaction between blood under shear stress and the induction of von Willebrand factor(VWF)damage.This research used a vortex oscillator blood-shearing platform to conduct in vitro experiments and used immunoblotting to quantify VWF damage in sheared samples to study the laws of shear-induced VWF damage under different shear stress,different exposure times,different blood components,and hemolysis conditions.It was found that VWF damage increased with exposure time and shear stress.At the same time,under lower shear stress,other blood components had little effect on VWF damage,while in a higher shear stress,other blood components would accelerate VWF damage.Hemolysis will also affect VWF damage,and the higher the degree of hemolysis,the higher the rate of VWF degradation in the plasma.The results of this research provide a reference for VWF damage evaluation standards and follow-up research and also guide for improving the design of ventricular assist devices to reduce VWF damage.

四分之一空间内椭圆孔对SH(shearing horizontal,反平面剪切)波的散射

利用保角变换和多极坐标移动技术,求解四分之一空间内含有椭圆孔时椭圆孔对入射平面SH(shearing hori-zontal)波的稳态散射问题。首先利用四分之一空间两垂直边界处的应力自由条件,写出不含椭圆孔时空间介质内的反射波场;其次,通过保角映射技术考虑空间介质内含有任意主轴方向的椭圆孔时,由于椭圆孔对入射和反射波场的散射作用而产生的散射波场,并预先使得该散射波场满足四分之一空间介质两垂直边界处的应力自由条件,利用叠加原理,将入射波场、反射波场和散射波场叠加起来,即可得到问题的总位移波场。最后借助于椭圆孔边界处的应力自由条件和傅里叶级数展开列出求解散射波解中未知系数的无穷代数方程组,在满足计算精度的前提下将方程组进行有限项截断,得到一个有限线性方程组并求解。通过算例具体讨论四分之一空间内椭圆孔边界处的环向动应力集中系数随入射波入射角、无量纲波数、椭圆孔方位参数的变化情况。

Electro-elastic Fields of Piezoelectric Materials with An Elliptic Hole under Uniform Internal Shearing Forces

The existing investigations on piezoelectric materials containing an elliptic hole mainly focus on remote uniform tensile loads. In order to have a better understanding of the fracture behavior of piezoelectric materials under different loading conditions, theoretical and numerical solutions are presented for an elliptic hole in transversely isotropic piezoelectric materials subjected to uniform internal shearing forces based on the complex potential approach. By solving ten variable linear equations, the analytical solutions inside and outside the hole satisfying the permeable electric boundary conditions are obtained. Taking PZT-4 ceramic into consideration, numerical results of electro-elastic fields along the edge of the hole and axes, and the electric displacements in the hole are presented. Comparison with stresses in transverse isotropic elastic materials shows that the hoop stress at the ends of major axis in two kinds of material equals zero for the various ratios of major to minor axis lengths; If the ratio is greater than 1, the hoop stress in piezoelectric materials is smaller than that in elastic materials, and if the ratio is smaller than 1, the hoop stress in piezoelectric materials is greater than that in elastic materials; When it is a circle hole, the shearing stress in two materials along axes is the same. The distribution of electric displacement components shows that the vertical electric displacement in the hole and along axes in the material is always zero though under the permeable electric boundary condition; The horizontal and vertical electric displacement components along the edge of the hole are symmetrical and antisymmetrical about horizontal axis, respectively. The stress and electric displacement distribution tends to zero at distances far from the elliptical hole, which conforms to the conclusion usually made on the basis of Saint-Venant's principle. Unlike the existing work, uniform shearing forces acting on the edge of the hole, and the distribution of electro-elastic fields inside and outside the elliptic hole are considered.

Formation of adiabatic shearing band for high-strength Ti-5553 alloy:A dramatic thermoplastic microstructural evolution

By using split Hopkinson pressure bar, optical microscopy and electronic microscopy, we investigate the influence of initial microstructures on the adiabatic shear behavior of high-strength Ti-5Al-5V-5Mo-3Cr(Ti-5553) alloy with lamellar microstructure and bimodal microstructure. Lamellar alloy tends to form adiabatic shearing band(ASB) at low compression strain, while bimodal alloy is considerably ASBresistant. Comparing with the initial microstructure of Ti-5553 alloy, we find that the microstructure of the ASB changes dramatically. Adiabatic shear of lamellar Ti-5553 alloy not only results in the formation of recrystallized β nano-grains within the ASB, but also leads to the chemical redistribution of the alloying elements such as Al, V, Cr and Mo. As a result, the alloying elements distribute evenly in the ASB.In contrast, the dramatic adiabatic shear of bimodal alloy might give rise to the complete lamination of the globular primary a grain and the equiaxial prior β grain, which is accompanied by the dynamic recrystallization of a lamellae and β lamellae. As a result, ASB of bimodal alloy is composed of a/β nanomultilayers. Chemical redistribution does not occur in ASB of bimodal alloy. Bimodal Ti-5553 alloy should be a promising candidate for high performance armors with high mass efficiency due to the processes high dynamic flow stress and excellent ASB-resistance.

Comparative Study on Shearing Edge Quality Influence of the Change of Tool Geometry in Fine-Blanking for Non-homogeneous Materials

Excellent quality of shearing edge implies that a s mo oth cutting edge without tearing will be observed on the whole edge surface. Thi s is one of the most significant features of the Fine-blanking process. To achi eve such a superb blanking edge quality in fine-blanking, there actually involv es quite a large number of factors, such as blanking speed, processing material, product shape, lubrication and tool geometry, to be considered simultaneously d uring the operation. Nevertheless, the thorough investigations on different effe cts of those critical factors for different kinds of popular and applicable mate rial are rare and limited. Thus, the objective of this paper is mainly focused o n the study of the quality influence of tool geometry change in fine-blanking f or non-homogeneous materials. However, the most obvious change of the tool geo metry during the operation will be the essential variation of the nose radius of the punch. This is because the nose radius usually seriously deteriorates with the increasing service period in mass production which eventually causes the ent irely lose of the specific features of the fine-blanking process. Therefore, a tailor-made experimental study was carried out to investigate the relationship between the punch nose radius and the shearing edge quality, such as blanked edg e finish, burr height and die-roll height, during fine-blanking for different types of material. Five punches with each specified nose radius (Rp), 0.00 mm, 0.25 mm, 0.50 mm, 0.75 mm and 1.00 mm, and four kinds of blanking material ( Mil d steel SS400, Stainless steel AISI316L, Copper alloy UNSC16200 and Aluminium al loy AA6063 ) were employed throughout the study. Subsequently, features of the s heared edge surfaces and data of each experiment were observed and captured for further analysis in this research. Consequently, findings show that an increase of punch nose radius would produce a higher percentage of fracture of blanked ed ge and increase the amount of burr height. In overall comparison, it is found th at mild steel and copper alloy do provide better surface edge finish with higher percentage of sheared area and less burr height than that of stainless steel an d aluminium alloy.

A CLOSED SYSTEM OF EQUATIONS FOR DENSE TWO-PHASE FLOW AND EXPRESSIONS OF SHEARING STRESS OF DISPERSED PHA’E AT A WALL

In this paper.each of the two phases in dense two-phase flow is considered ascontinuous medium and the fimdamental equations for two-phase flow are described inEulerian form.The generalized constitutive relation of the Bingham fluid is applied to thedispersed phase with the analysis of physical mechanism of of dense two-phase flow.Theshearing stress of dispersed phase at a wall is used to give a boundary condition.Then amathematical model for dense two-phase flow is obtained.In addition.the expressions ofshearing stress of dispersed phase at a wall is derived according to the fundamental,model ofthe frictional collision between dispersed-phase particles and the wall.

Analysis of Photoelectric Hybridization Measurement on Shearing Force for Flat Shearer

This paper introduces a kind of photoelectric hybridization measuring process.Owing to the characteristics of the compact form of shearing equipment to be analyzed and the connecting rod existing in two directional stress state during operation etc.,it is hard to obtain results by means of single electrical testing process.For this reason,this paper derives a group of calculation formulas of hybridization measuring process through comprehensive discussion of photoelectric analysis and electrical testing theories,thus providing an analytical method for actual measurement of complex engineering problems.

The Micro-Scale Mechanism of Metal Mine Tailings Thickening Concentration Improved by Shearing in Gravity Thickener

Higher concentration is beneficial for the Paste and Thickened Tailings(PTT)operation in metal mine.Partial paste thickeners are produced lower density underflow.Flocculated tailings are intended to form a water entrapped network structure in thickener,which is detrimental to underflow concentration.In this study,the continuous thickening experiment was carried out for ultra-fine tungsten tailings to study the influence of rake shearing on underflow.The micro pores structure and seepage flow in tailings bed before and after shearing are studied by CT and simulation approach to reveal the shearing enhancement mechanism of thickening process.The results shown that,the underflow concentration is increased from 61.4 wt%to 69.6 wt%by rake shearing in a pilot scale thickener,the porosity decreased from 46.48%to 37.46%.The entrapped water discharged from sticks structure more than sphere spaces.In items of seepage,after shearing,the seepage flow channel of tailings underflow is becoming longer,which caused the decreasing average flow rate decreases and absolute permeability.The absolute permeability is negatively correlated with tortuosity.The rake shearing can destroy the flocs structure;change the effective stress to increase the concentration.Higher underflow concentration improves the waste recycling and water recovery rate,especially for arid areas.

Broad-band phase retrieval method for transient radial shearing interference using chirp Z transform technique

The transient radial shearing interferometry technique based on fast Fourier transform(FFT)provides a means for the measurement of the wavefront phase of transient light field.However,which factors affect the spatial bandwidth of the wavefront phase measurement of this technology and how to achieve high-precision measurement of the broad-band transient wavefront phase are problems that need to be studied further.To this end,a theoretical model of phase-retrieved bandwidth of radial shearing interferometry is established in this paper.The influence of the spatial carrier frequency and the calculation window on phase-retrieved bandwidth is analyzed,and the optimal carrier frequency and calculation window are obtained.On this basis,a broad-band transient radial shearing interference phase-retrieval method based on chirp Z transform(CZT)is proposed,and the corresponding algorithm is given.Through theoretical simulation,a known phase is used to generate the interferogram and it is retrieved by the traditional method and the proposed method respectively.The residual wavefront RMS of the traditional method is 0.146λ,and it is 0.037λfor the proposed method,which manifests an improvement of accuracy by an order of magnitude.At the same time,different levels of signal-to-noise ratios(SNRs)from 50 dB to 10 dB of the interferogram are simulated,and the RMS of the residual wavefront is from 0.040λto 0.066λ.In terms of experiments,an experimental verification device based on a phase-only spatial light modulator is built,and the known phase on the modulator is retrieved from the actual interferogram.The RMS of the residual wavefront retrieved through FFT is 0.112λ,and it decreases to 0.035λthrough CZT.The experimental results verify the effectiveness of the method proposed in this paper.Furthermore,the method can be used in other types of spatial carrier frequency interference,such as lateral shearing interference,rotational shearing interference,flipping shearing interference,and four-wave shearing interference.

ON THE ENERGY STORAGE IN A SOLAR ACTIVE REGION AR 5395 BY SHEARING MAGNETIC FIELD (ABSTRACT)

There is a rotation movement continuoslly in a solar active region AR5395. Themagnetic configuration of the active region was reconstructed after a series of the largeflares occured. In this paper a sheared open magnetic arcade model of flares was

Gelation of <i>Antheraea pernyi</i>Silk Fibroin Accelerated by Shearing

The rapid manufacture of silk fibroin gels in mild conditions is an important subject in the field of silk-based biomaterials. In this study, the gelation of Antheraea pernyi silk fibroin (ASF) aqueous solution was induced by shearing, without chemical cross-linking agents. Simple shearing controlled and accomplished the steady and rapid conformational transition to β-sheets with ease. The conformational transformation and rapid gelation mechanisms of ASF induced by shearing were tracked and analyzed by circular dichroism spectrometry, Fourier transform infrared spectroscopy and X-ray diffractometry, then compared with Bombyx mori silk fibroin (BSF). ASF quickly formed hydrogels within 24 - 48 h after shearing under different shearing rates for 30 - 90 min, resulting in sol-gel transformation when the β-sheet content reached nearly 50%, which is the minimum content needed to maintain a stable hydrogel system in ASF. The gel structures remained stable once formed. The rapid gelation of ASF through shearing compared with BSF was achieved because of ASF’s alternating polyalanine-containing units, which tend to form α-helix structures spontaneously. Further, the entropic cost during the conformational transition from the α-helix to the β-sheet structure is less than the cost of the transition from the random coil structure. This method is a simple, non-chemical cross-linking approach for the promotion of rapid gelation and the protection of the biological properties of ASF, and it may prove useful for application in the field of biomedical materials.

Effects of bolt profile and grout mixture on shearing behaviors of bolt-grout interface

Shearing behavior and failure mechanism of bolt-grout interface are of great significance for load transfer capacity and design of rock bolting system.In this paper,direct shear tests on bolt-grout interfaces under constant normal load(CNL) conditions were conducted to investigate the effects of bolt profile(i.e.rib spacing and rib height) and grout mixture on the bolt-grout interface in terms of mechanical behaviors and failure modes.Test results showed that the peak shear strength and the deformation capacity of the bolt-grout interface are highly dependent on the bolt profile and grout mixture,suggesting that bolt performances can be optimized,which were unfortunately ignored in the previous studies.A new interface failure mode,i.e.'sheared-crush' mode,was proposed,which was characterized by progressive crush failure of the grout asperities between steel ribs during shearing.It was shown that the interface failure mode mainly depends on the normal stress level and rib spacing,compared with the rib height and grout mixture for the range of tested parameters in this study.

Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading

The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China.The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software.Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing,and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity.The macroscopic properties and damage patterns were obtained for six numerical configurations;namely,loess-weathered mudstone with 0°,10°,and-10°joints and weathered mudstone with 0°,10°,and-10°weak intercalated layers.The numerical test results revealed that,in the direct shear tests,the shear stress and shear displacement of the samples increased with the normal stress.In the cyclic shear tests with a total cycle number N=20,the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop.The numerical tests also revealed that,under cyclic shear,the normal stress and shear velocity affected the shear strength.The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations.Compared with the damage pattern of the direct shear tests,the damage of the cyclic shear tests mainly comprised shear cracks and fractures,some shaking consolidation settlement and fewer shear strain occurred around the joints.In the direct shear tests,more compression cracks and fractures occurred in the samples.The damage mainly developed along the joints,and shearing-off damage occurred.The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China.

A MODIFIED METHOD IN FINITE ELEMENT ANALYSIS WITH APPLICATION TO SIMPLE SHEARING

A modified technique called compatible stress iterative procedure isproposed in finite element analysis,which has well improved the conventionalweighted-residual method and was successful in dealing with the formation andlocalization process of shear banding.

A five-parameter constitutive model for hysteresis shearing and energy dissipation of rock joints

Rock joints exhibit hysteresis shearing behavior and produce energy dissipation under shear cyclic loads,which however cannot be accurately depicted by existing constitutive models. This paper establishes a constitutive model for hysteresis shearing and associated energy dissipation of rock joints. Analytical expressions of the model during cyclic shearing processes are derived. Derivation of the model indicates no energy dissipation in the elastic stage. When the shear load exceeds elastic boundary, nonlinear energy dissipation takes place. Validations with experiments show that the proposed model provides good conformities with direct shear curves and hysteresis loops, and can predict the energy dissipation characteristics of rock joints under different working conditions. Compared to the constitutive models using Weibull's distribution, the proposed one is smooth at the elastic boundary and can accurately capture the maximum shear stress. Unlike the existing incremental-type models, the proposed one provides clear and direct analytical expressions for both shear stress and energy dissipation during the whole displacement domain, which is more convenient in application.

An approach to measure infill matric suction of irregular infilled rock joints under constant normal stiffness shearing

Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers(HCTs) during direct shear of infilled joints under constant normal stiffness(CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using threedimensional(3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients(JRCs) of 8-10 and 18-20 with the ratios of infill thickness to asperity height(t/a)equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness.

NON-LINEAR WATER WAVES ON SHEARING FLOWS

This article is devoted to the study of the propagations of the non-linear water waves on the shear flows. Assuming μ = kh is small and ε/μ~2 ～ 0 (1),and the base flow is uniformly sheared, the modified Boussinesq equation is obtained.We calculate propagations of the single sohtary wave with vorticity Γ = 0, 】0 and【0. The influences of the vorticity are manifested. At the end examples of theinteractions of two solitary waves, moving in opposite and the same directions, aregiven. Besides the phase shift, there also occur second wavelets after head-on collision.

Correlation Between Yield Stress of Silty Mud Sediments and Continuous Oscillatory Shearing Properties

Analyzing the rheological properties of silty beds subjected to continuous oscillatory shear loading is crucial for understanding the morphological deformation of the seabed and ensuring safety in geological and marine engineering applications.In this study,the effects of oscillatory shearing properties on the yield stress(S_(u))of silty sediments were quantitatively investigated.The effects of oscillatory shear strength(0-3),water content(26.6%-70.84%),and particle diameter(8.79-50μm)were examined extensively through a series of laboratory tests.The results indicated that the three aforementioned parameters were the major factors that affected the rheological characteristics of silty sediments.Furthermore,their effects could be elucidated using the yield stress of cohesive sediments as the indicator parameter.The ratio of yield stress(S_(u)/S_(u0))varied as the oscillatory shear strength increased up to a critical value,Λ_(cr).S_(u)bsequently,the ratio remained at a constant value.It was deduced that the yield stress decreased with increasing oscillatory shear strength forΛ<Λ_(cr),when the sediments were in a non-equilibrium fluidization stage.WhenΛ>Λ_(cr),the sediments entered an equilibrium fluidization stage,and the yield stress remained almost constant,irrespective of the oscillatory shear strength.Furthermore,during the equilibrium fluidization stage,it was observed that the ratio S_(u)/S_(u0)did not vary with water content but decreased as the particle diameter increased.Finally,based on regression analysis of the experimental data for non-equilibrium and equilibrium fluidization stages,a correlation between yield stress of silty sediments and continuous oscillatory shearing properties was proposed.This correlation can aid in understanding the changes in solid resistance and assessing safety in piling engineering.Furthermore,it can provide a theoretical guidance for reducing soil resistance in marine structures using mechanical vibrations.

Determination of Shearing Properties for Tubular Pinewood under Torsion

In this study, tubular pinewood (Pinus sylvestris L.) specimens are tested and shear strain measurements are performed by applying torsion in z direction in the consideration of light weight aircraft engineering. The objective of this paper is to contribute and generate the nonlinear material model in terms of shear modulus presented with power functions under the consideration of nonlinear behavior of wood under torque. Strain gauge measurements are performed for the maximum shear stresses which develop on the tubular specimen, along the radial r(rin, rout), circumferential Φ(Φin, Φout) and z directions, in a point-wise manner. The data is gathered and examined for the determination of the local variations of empirical shear modulus functions on transversely isotropic surfaces of the specimens. The coordinate dependent shear modulus functions of GzΦ(r), GzΦ(Φ), GzΦ(z) are derived for GzΦ(r, Φ, z)as the function of r, Φ and z, respectively, by analyzing the gathered data. It is proposed to represent the shear modulus functions, GzΦ(Φ) and GzΦ(z) with the parabolic polynomials, and, to represent the shear modulus function GzΦ(r) with a linear equation.