Shear transformation zone dependence of creep behaviors of amorphous phase in a CuZr-based bulk metallic glass composite

The creep behaviors of the amorphous phase in a CuZr-based bulk metallic glass composite(BMGC)are studied by nanoindentation.Samples fabricated via higher cooling rates are found to exhibit more prominent creep,but a smaller shear viscosity.The volume of the shear transformation zones(STZs)in the amorphous phase calculated based on a cooperative shear model increases with the cooling rate.The evolution of excess free volume created during creep deformation is clarified.A looser atomic arrangement leads to a larger STZ volume,thus facilitating creep deformation.This study gives a better understanding of the deformation behaviors of the amorphous phase in BMGCs.

Deformation, Phase Transformation and Recrystallization in the Shear Bands Induced by High-Strain Rate Loading in Titanium and Its Alloys

α-titanium and its alloys with a dual-phase structure （α＋β） were deformed dynamically under strain rate of about 10^4 s^-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate （9×10^5 S^-1） deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations in the bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products （α2） had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10 μm in diameter observed within the bands are proposed to be the results of recrystallization.

Phenomenon of transformed adiabatic shear band surrounded by deformed adiabatic shear band of ductile metal

The coexistent phenomenon of deformed and transformed adiabatic shear bands(ASBs) of ductile metal was analyzed using the JOHNSON-COOK model and gradient-dependent plasticity(GDP).The effects of melting point,density,heat capacity and work to heat conversion factor were investigated.Higher work to heat conversion factor,lower density,lower heat capacity and higher melting point lead to wider transformed ASB and higher local plastic shear deformation between deformed and transformed ASBs.Higher work to heat conversion factor,lower density,lower heat capacity and lower melting point cause higher local plastic shear deformation in the deformed ASB.Three reasons for the scatter in experimental data on the ASB width were pointed out and the advantages of the work were discussed.If the transformed ASB width is used to back-calculate the internal length parameter in the GDP,undoubtedly,the parameter will be extremely underestimated.

一个新的基于3D纹理映射及Shear-warp变换的快速体绘制方法

介绍了一个新的基于纹理映射及Shear-warp变换的快速体绘制方法。所提出的方法吸收了纹理映射方法的长处，通过纹理硬件的加速，并在纹理装载时提出了可适应性的纹理分割方法，使该算法不受纹理内存的限制。在进行纹理映射时，通过剪切（Shear）变换和三维图象的分割，加快给制速度。与多种经典的快速体绘制方法进行测试比较，该方法达到了交互的效果和更高的绘制速度。

基于Shear变换的彩色地形图混沌加密算法

针对目前研究地形图图像加密算法较少,以及现有图像加密算法易被破解的问题,提出基于Shear变换的彩色地形图混沌加密算法。该算法充分利用了Shear变换的多方向性,能够很好地对地形图的线划要素信息进行置乱的特点,以及Lorenz混沌系统具有极强初值敏感性和更大的密匙空间和安全性的特点。通过对彩色地形图的加密和解密实验,以及抗攻击性能对比实验,表明使用该算法加密后的彩色地形图具有更高的安全性,并且载体图像具有较高的抗攻击性能。

Analytical Solution for Wave-Induced Response of Seabed with Variable Shear Modulus

A plane strain analysis based on the generalized Biot＇s equation is utilized to investigate the wave-induced response of a poro-elastic seabed with variable shear modulus. By employing integral transform and Frobenins methods, the transient and steady solutions for the wave-inducod pore water pressure, effective stresses and displacements are analytically derived in detail. Verification is available through the reduction to the simple case of homogeneous seabed. The numerical results indicate that the inclusion of variable shear modulus significantly affects the wave-induced seabed response.

Microstructural Evolution of Localized Shear Bands Induced during Explosion in Ti-6Al-4V Alloy

Microstructures of the localized shear bands generated during explosion with a thick-walled cylinder specimen in Ti-6AI-4V alloy, were characterized by TEM and SEM. The results show that the twinning is a major mode of deformation, and the distortion-free grains in the bands with the size of 10μm in diameter were proposed to be the re-crystallization during dynamic explosion. The further observations show that the α→α2 phase transformation may occur in the bands, and this kind of transformation could be confirmed by its dark field image and electron diffraction analysis. Analysis shows that there is specified orientation between the α and α2 Phases.

Shear strength criteria for rock,rock joints,rockfill and rock masses:Problems and some solutions

Although many intact rock types can be very strong,a critical confining pressure can eventually be reached in triaxial testing,such that the Mohr shear strength envelope becomes horizontal.This critical state has recently been better defined,and correct curvature or correct deviation from linear Mohr-Coulomb（MC） has finally been found.Standard shear testing procedures for rock joints,using multiple testing of the same sample,in case of insufficient samples,can be shown to exaggerate apparent cohesion.Even rough joints do not have any cohesion,but instead have very high friction angles at low stress,due to strong dilation.Rock masses,implying problems of large-scale interaction with engineering structures,may have both cohesive and frictional strength components.However,it is not correct to add these,following linear M-C or nonlinear Hoek-Brown（H-B） standard routines.Cohesion is broken at small strain,while friction is mobilized at larger strain and remains to the end of the shear deformation.The criterion ＇c then σn tan φ＇ should replace ＇c plus σn tan φ＇ for improved fit to reality.Transformation of principal stresses to a shear plane seems to ignore mobilized dilation,and caused great experimental difficulties until understood.There seems to be plenty of room for continued research,so that errors of judgement of the last 50 years can be corrected.

INVESTIGATION OF THE SCATTERING OF ANTI-PLANE SHEAR WAVES BY TWO GRIFFITH CRACKS USING THE NON-LOCAL THEORY

In this paper, the scattering of harmonic antiplane shear waves bytwo finite cracks is studied using the non-local theory. The Fouriertransform is applied and a mixed boundary value prob- lem isformulated. Then a set of triple integral equations is solved using anew method, namely Schimidt's method. This method is more exact andmore reasonable than Erigen's for solving this Kind of problem. Theresult of the stress near the crack tip was obtained. Contrary to theclassical elas- Ticity solution, it is found that no stresssingularity is present at the crack tip, which can explain theProblem of macroscopic and microscopic mechanics.

Bone morphogenetic protein-4 and transforming growth factor-beta1 mechanisms in acute valvular response to supra-physiologic hemodynamic stresses

AIM:To explore ex vivo the role of bone morphogenetic protein-4(BMP-4) and transforming growth factorbeta1(TGF-β1) in acute valvular response to fluid shear stress(FSS) abnormalities.METHODS:Porcine valve leaflets were subjected ex vivo to physiologic FSS,supra-physiologic FSS magnitude at normal frequency and supra-physiologic FSS frequency at normal magnitude for 48 h in a double-sided cone-and-plate bioreactor filled with standard culture medium. The role of BMP-4 and TGF-β1 in the valvular response was investigated by promoting or inhibiting the downstream action of those cytokines via culture medium supplementation with BMP-4 or the BMP antagonist noggin,and TGF-β1 or the TGF-β1 inhibitor SB-431542,respectively. Fresh porcine leaflets were used as controls. Each experimental group consisted of six leaflet samples. Immunostaining and immunoblotting were performed to assess endothelial activation in terms of intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expressions,paracrine signaling in terms of BMP-4 and TGF-β1 expressions and extracellular matrix(ECM) remodeling in terms of cathepsin L,cathepsin S,metalloproteinases(MMP)-2 and MMP-9 expressions. Immunostained images were quantified by normalizing the intensities of positively stained regions by the number of cells in each image while immunoblots were quantified by densitometry. R E S U LT S :Regardless of the culture medium,physiologic FSS maintained valvular homeostasis. Tissue exposure to supra-physiologic FSS magnitude in standard medium stimulated paracrine signaling(TGF-β1:467% ± 22% vs 100% ± 6% in freshcontrols,BMP-4:258% ± 22% vs 100% ± 4% in fresh controls; P < 0.05) and ECM degradation(MMP-2:941% ± 90% vs 100% ± 19% in fresh controls,MMP-9:1219% ± 190% vs 100% ± 16% in fresh controls,cathepsin L:1187% ± 175% vs 100% ± 12% in fresh controls,cathepsin S:603% ± 88% vs 100% ± 13% in fresh controls; P < 0.05),while BMP-4 supplementation also promoted fibrosa activation and TGF-β1 inhibition reduced MMP-9 expression to the native tissue level(MMP-9:308% ± 153% with TGF-β1 inhibition vs 100% ± 16% in fresh control; P > 0.05). Supra-physiologic FSS frequency had no effect on endothelial activation and paracrine signaling regardless of the culture medium but TGF-β1 silencing attenuated FSS-induced ECM degradation via MMP-9 downregulation(MMP-9:302% ± 182% vs 100% ± 42% in fresh controls; P > 0.05).CONCLUSION:Valvular tissue is sensitive to FSS abnormalities. The TGF-β1 inhibitor SB-431542 is a potential candidate molecule for attenuating the effects of FSS abnormalities on valvular remodeling.

ASYMPTOTIC ANALYSIS OF PLANE-STRAIN MODE I STEADY-STATE CRACK GROWTH IN TRANSFORMATION TOUGHENINGCERAMICS(Ⅱ)

Based on a constitutive law which includes the shear components oftransformation plasticity. the asymptotic solutions to near-tip fields of plane-strainmode I steadity propagating cracks in rransformed ceramics are obtained for the caseof linear isotropic hardening. The Stress singularity. the distributions of stresses andvelocities at the crack tip are determmed for various material parameters. The factorsinfluencing the near-tip fields are discussed in detail.

基于NSST域像素相关性分析的融合算法在医学图像中的评估

多尺度变换对医学图像融合有较好的效果。针对MRI与CT、SPECT、PET的脑部图像融合,采用基于非下采样剪切波变换(NSST)域像素相关性分析(PCAS)的图像融合算法进行评估,体现出较好的稳定性和鲁棒性。

THE GENERAL SOLUTION OF SECOND ORDER EFFECTS IN ELASTIC HALF-SPACE ACTED UPON BY A NON-UNIFORM SHEAR LOAD

This paper is a continuation of [1]. A closed form solution to the second order elasticity problem, when an isotropic compressible elastic half-space undergoes a deformation owing to a non-uniformly distributed shear load, is presented. The method of integral transform is employed to determine the solutions.

THE ILLUSTRATION CALCULATIONS OF SECOND ORDER EFFECTS IN ELASTIC HALF-SPACE ACTED UPON BY A NON-UNIFORM SHEAR LOAD

This paper is a continuation of [1]. An example is discussed in derail to illustrate the second order effects. Numerical calculations for the second order elastic material for the z-direction displacement and the stress t(rz) are carried out. It is found that the second order effect is to reduce z-direction displacement and to decrease t(rz)inside the circle but to increase its value outside the circle.

Transformation Matrix for Combined Loads Applied to Thin-Walled Structures

This paper transforms combined loads, applied at an arbitrary point of a thin-walled open section beam, to the shear centre of the cross-section of the beam. Therein, a generalized transformation matrix for loads with respect to the shear centre is derived, this accounting for the bimoments that develop due to the way the combined loads are applied. This and the authors’ earlier paper (World Journal of Mechanics 2021, 11, 205-236) provide a full solution to the theory of thin-walled, open-section structures bearing combined loading. The earlier work identified arbitrary loading with the section’s area properties that are necessary to axial and shear stress calculations within the structure’s thin walls. In the previous paper attention is paid to the relevant axes of loading and to the transformations of loading required between axes for stress calculations arising from tension/compression, bending, torsion and shear. The derivation of the general transformation matrix applies to all types of loadings including, axial tensile and compression forces, transverse shear, longitudinal bending. One application, representing all these load cases, is given of a simple channel cantilever with an eccentrically located end load.

Temperature distribution in adiabatic shear band for ductile metal based on JOHNSON-COOK and gradient plasticity models

Gradient-dependent plasticity considering interactions and interplay among microstructures was included into JOHNSON-COOK model to calculate the temperature distribution in adiabatic shear band(ASB), the peak and average temperatures as well as their evolutions. The differential local plastic shear strain was derived to calculate the differential local plastic work and the temperature rise due to the microstructural effect. The total temperature in ASB is the sum of initial temperature, temperature rise at strain-hardening stage and non-uniform temperature due to the microstructural effect beyond the peak shear stress. The flow shear stress—average plastic shear strain curve, the temperature distribution, the peak and average temperatures in ASB are computed for Ti-6Al-4V. When the imposed shear strain is less than 2 and the shear strain rate is 1 000 s?1, the dynamic recovery and recrystalliza-tion processes occur. However, without the microstructural effect, the processes might have not occurred since heat diffusion decreases the temperature in ASB. The calculated maximum temperature approaches 1 500 K so that phase transformation might take place. The present predictions support the previously experimental results showing that the transformed and deformed ASBs are observed in Ti-6Al-4V. Higher shear strain rate enhances the possibility of dynamic recrystallization and phase transformation.

爆炸加载TC4 ELI钛合金微损伤研究

用TNT炸药空中爆炸加载等轴组织TC4 ELI钛合金板材,研究爆炸药量及距靶板中心距离对钛合金显微组织演化的影响,测试了爆炸加载后材料的力学性能。结果表明:爆炸加载后TC4 ELI钛合金显微组织内产生了大量形变带,形变带宽度为10~120μm;随着爆炸药量从200 g提高到300 g,形变带的数量及总宽度增加,形变带边界更加清晰;随着距靶板中心距离的增加,形变带数量不变,宽度增加。对爆炸加载回收靶板采用分离式霍普金森压杆(SHPB)进行动态压缩再加载试验,随药量和距靶板中心距离的增加,钛合金静动态抗压强度与断裂应变增加。动态再加载后产生了绝热剪切转变带,形变带对转变带的萌生及扩展过程影响较小。

基于图像能量和NSST的电力设备发热定位方法

为了解决现有红外检测技术中电力设备发热点定位不够准确的问题,基于图像能量和非下采样剪切波变换,提出了一种实时监测方法。结合红外图像灰度与温度的关系,使用了图像能量算法和种子生长算法对红外图像进行分割;同时在分析终端使用非下采样剪切波变换融合可见光与红外图像,提高了发热区域的定位精准度;对发热特征进行分析,减小了误判、漏判情况出现的概率。研究结果表明,所提方法为电力设备故障发热区域定位提供了有效信息,可用于在线监测与故障定位。

基于剪切波变换和脉冲耦合神经网络的图像融合方法研究

图像融合的目的是将多个来源的图像合并,从而产生1个包含所有原始图像信息的新图像。传统的图像融合方法可能损失一些重要信息或导致图像失真,因此研究新的图像融合方法具有重要意义。作为新兴技术,剪切波变换和脉冲耦合神经网络在图像融合中的应用潜力尚未被充分发掘。文章致力于研究这2种技术在图像融合中的效果,并提出结合两者的新方法。

含孔洞Cu_(64)Zr_(36)及Cu/Cu_(64)Zr_(36)复合材料拉伸变形的分子动力学研究

本工作采用分子动力学模拟研究了含孔洞Cu_(64)Zr_(36)金属玻璃和Cu/Cu_(64)Zr_(36)晶体/非晶复合材料的拉伸变形行为。结果表明:Cu_(64)Zr_(36)金属玻璃在加载过程中由孔洞引起的应变集中导致剪切转变区(STZ)被激活并诱发剪切带的形成,而Cu/Cu_(64)Zr_(36)复合材料通过晶体相中的位错滑移有效避免了灾难性剪切局部化,阻碍了剪切带的扩展。应变局部化程度出现台阶式的跳跃主要由位错的成核和发射引起,而应变局部化程度的缓慢增加与STZ的激活有关,一旦剪切带形成会导致应变局部化程度的快速增加。孔洞的存在改变了剪切应变和非仿射平方位移的分布,原子剪切应变和非仿射平方位移最小值D_(min)^(2)的最大值总是分布在孔洞周围,使其成为最有可能位错成核、STZ激活并诱发剪切带形成的位点。大量的位错运动和均匀的STZ激活是提高复合材料整体塑性的主要原因,晶体相中位错密度的变化与非晶相中的剪切带活动密切相关。当剪切带扩展受阻,只出现均匀的STZ激活,位错密度基本保持不变,应力累积。一旦STZ局部化,重新诱发剪切带的扩展,位错密度增加和应力释放,这也是Cu/Cu_(64)Zr_(36)复合材料应力波动的主要原因。