Shear stress distribution and characteristics of deformation for shear band-elastic body system at pre-peak and post-peak

The distributed shear stress and the displacement across shear band, the evolution of plastic zones, and the load-carrying capacity of rock specimen were investigated in plane strain direct shear test according to Fast Lagrangian Analysis of Continua （FLAC）. And then the shear displacement distribution in normal direction of system composed of localized shear band and elastic rock was analyzed based on gradient-dependent plasticity. The adopted failure criterion was a composite of Mohr-Coulomb criterion, that is, the relation between tension cut-off and postpeak constitutive of rock was linear strain-softening. Numerical results show that shear stress field approximately undergoes three different stages. At first, shear stress is only concentrated in the middle of top and base of specimen. Next, shear stress in the middle of specimen tends to increase, owing to superposition of shear stresses. Interestingly, two peaks of shear stress appear far from the loading ends of specimen, and the peaks approach with the increase in timestep until elements at the center of specimen yield. Finally, relatively lower shear stress level is reached in large part of specimen except in the regions near the two ends. As flow stress decreases, the analytical shear displacement distribution in shear band based on gradient-dependent plasticity becomes steeps outside the band, it is linear and its slope tends to decrease. These theoretical results qualitatively agree with that of the present numerical predicted results. Main advantage of the analytical solution over the numerical results according to FLAC is that it is continuous, smooth and non-linear （except at elastic stage）.

Theoretical Analysis and Experimental Verification of Crack Initiation Characteristics of Compression-Shear Plane Crack with Hydraulic Pressure

In this paper, the crack initiation characteristics of compression-shear plane crack with hydraulic pressure were studied by using theoretical analysis and experimental verification methods. The formula derivation process of stress intensity factor of crack tip and open-type crack initiation angle and initiation strength was expounded in detail. Cement mortar specimens prefabricated with open-type crack were made for biaxial compression test. The results show that the mode I stress intensity factor is inversely proportional to the dip angle of pre-exciting crack, water pressure and crack width. The fracture toughness is most easily achieved when the dip angle of pre-exciting crack is 60°. The mode II stress intensity factor is symmetrically distributed with the dip angle and independent of the water pressure and crack width. For open-type crack, the crack initiation angle decreases with the increase of the dip angle of pre-exciting crack, water pressure and crack width;the crack initiation strength is inversely proportional to the water pressure and proportional to the lateral pressure. The research results can provide ideas for the study of crack initiation under the coupling of ground stress and osmotic pressure in tunnel engineering.

Dynamic anti-plane analysis for two symmetrically interfacial cracks near circular cavity in piezoelectric bi-materials

The present paper is exposed theoretically to the influence on the dynamic stress intensity factor （DSIF） in the piezoelectric bi-materials model with two symmet- rically permeable interracial cracks near the edges of a circular cavity, subjected to the dynamic incident anti-plane shearing wave （SH-wave）. An available theoretical method to dynamic analysis in the related research field is provided. The formulations are based on Green＇s function method. The DSIFs at the inner and outer tips of the left crack are obtained by solving the boundary value problems with the conjunction and crack- simulation technique. The numerical results are obtained by the FORTRAN language program and plotted to show the influence of the variations of the physical parameters, the structural geometry, and the wave frequencies of incident wave on the dimensionless DSIFs. Comparisons with previous work and between the inner and outer tips are con- cluded.

Analysis of mode Ⅲ crack perpendicular to the interface between two dissimilar strips

The present work is concerned with the problem of mode Ⅲ crack perpendicular to the interface of a bi-strip composite. One of these strips is made of a functionally graded material and the other of an isotropic material, which contains an edge crack perpendicular to and terminating at the interface. Fourier transforms and asymptotic analysis are employed to reduce the problem to a singular integral equation which is numerically solved using Gauss-Chebyshev quadrature formulae. Furthermore, a parametric study is carried out to investigate the effects of elastic and geometric characteristics of the composite on the values of stress intensity factor.

Cyclic behavior of reinforced sand under principal stress rotation

Although the cyclic rotation of the principal stress direction is important,its effect on the deformation behavior and dynamic properties of the reinforced soil has not been reported to date.Tests carried out on large-scale hollow cylinder samples reveal that the cyclic rotation of the principal stress direction results in significant variations of strain components(ε,ε,εand γ) with periodic characteristics despite the deviatoric stress being constant during tests.This oscillation can be related to the corresponding variations in the stress components and the anisotropic fabric that rotate continuously along the principal stress direction.Sand under rotation appears to develop a plastic strain.Similar trends are observed for reinforced sand,but the shear interaction,the interlocking between particles and reinforcement layer,and the confinement result in significant reductions in the induced strains and associated irrecoverable plastic strains.Most of the strains occur in the first cycle,and as the number of cycles increases,the presence of strains becomes very small,which is almost insignificant.This indicates that the soil has reached anisotropic critical state(ACS),where a stable structure is formed after continuous orientation,realignment and rearrangement of the particles accompanied with increasing cyclic rotation.Rotation in the range of 60°-135° produces more induced strains even in the presence of the reinforcement,when compared with other ranges.This relates to the extension mode of the test in this range in which σ>σand to the relative approach between the mobilized plane and the weakest horizontal plane.Reinforcement results in an increase in shear modulus while it appears to have no effect on the damping ratio.Continuous cycles of rotation result in an increase in shear modulus and lower damping ratio due to the densification that causes a decrease in shear strain and less dissipation of energy.

Analytical investigation on mean and turbulent velocity fields of a plane jet

This paper analyses the downstream developments of the mean and the turbulent velocity fields of a plane jet. Based on the conservation of mass and the conservation of momentum, the mean-velocity half width （reflecting the jet spread rate） and the relative mass flow rate （jet entrainment） are related to the decay rate of the centreline mean velocity. These relations are not subject to self-preservation. Both analytical and experimental results suggest that the jet spread rate （K1） and the entrainment rate （K3） （and thus the decay rate K2） can be well estimated from the centreline velocity, i.e., K1 ≈ 0.6K2 and K3 ∝K2. The effect of initial mean velocity and RMS velocity profiles on the downstream mean velocity field appears to be embodied in the constants K1 K2 and K3. The analytical relationship for the self-preserving Reynolds shear stress, obtained for the first time, works well.

THE ANALYSES OF THE THREE-DIMENSIONAL STRESS STRUCTURE NEAR THE CRACK TIP OF MODE Ⅰ CT SPECIMENS IN ELASTICPLASTIC STATE(Ⅱ)--THE ANALYSES OF THE STRESS STRUCTURE

Based on[1],the stress structures of the smooth region and shear lip of the specimens have been investigated in the paper.The characteristics of the stress structure in the smooth region have been found that the variable z can separated out;the stresses in the midsection can be obtained by the plane strain FEM results or HRR structure modified by the stress triaxiality.The effects of load level and thickness on the stress structure can be reflected by the distribution of CTOD along the thickness direction.The obtained expressions of the stresses are very simple and visualized.The analyses of the stress structure in the shear lip show that the stresses can be obtained by different methods of interpolation to a certain precise degree.A new degree parameter of the plane strain state has been put forward and studied.The parameter can reflect relatively well the variation of the kind and thickness of the specimen as well as the load level.The fracture parameter has also been investigated to be sure that it can be obtained by modified CTOD with the stress triaxiality.

PROBLEMS OF COLLINEAR CRACKS BETWEEN BONDED DISSIMILAR MATERIALS UNDER ANTIPLANE CONCENTRATED FORCES

In this paper problems of collinear cracks between bonded dissimilar materials under antiplane concentrated forces are dealt with. General solutions of the problems are formulated by applying extended Schwarz principle integrated with the analysis of the singularity of complex stress functions. Closed-form solutions of several typical problems are obtained and the stress intensity factors are given. These solutions include a series of original results and some results of previous researches. It is found that under symmetrical loads the solutions for the dissimilar materials are the same as those for the homogeneous materia[7]

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。

A Review of the Calculation Formula for the Four-component Borehole Strainmeter and Application to Earthquake Cases

Based on the principle formula for the four-component strainmeters, we can directly obtain the specific plane strain, shear strain and azimuthal angle of the principal strain, and the maximum and minimum principal strains calculated afterwards are the indirect result. The problems of practicality of the sensitivity coefficients A and B of plane strain and shear strain are then discussed. Based on this idea, we analyzed the observation data of several four-component borehole strainmeters near the epicenter of the Yiliang M_S5.7 earthquake in 2012 and the Ludian M_S6.5 earthquake in 2014 in the Zhaotong area, Yunnan Province. The results show that the analysis based on the perspective of plane strain and shear strain has an obviously better effect than that based on the component readings, and can directly peel off the respective abnormality of the plane strain and shear strain. In addition, the correlation coefficient curves between measured data of two plane strains show significant anomalies which often occur several days before and during the earthquake.

Drucker-Prager准则参数特性分析

Drucker-Prager准则在数值计算中得到广泛运用。但如果该准则的参数选取不当,可能导致预测与试验结果之间不一致。通过分析函数基本特性,考察该准则反映中主应力对强度参数影响的能力,探讨导致预测与试验结果之间不一致的可能原因。进而对目前常用的参数表达式进行详细的分析,并考察平面应变情况下Drucker-Prager准则的参数特性。分析表明:Drucker-Prager准则不能合理地反映中主应力对强度参数的影响,且在平面应变情况下会得出中主应力系数小于0的结论。

压缩剪切平面应变试样的应力状态响应

为模拟金属塑性变形过程中的压缩剪切应力状态的平面应变特征,构建了平面压缩剪切试样。通过数字图像相关(DIC)技术和有限元模拟表征变形区Y方向的应力状态分布特征及压缩断裂过程。DIC结果显示,在压缩实验过程中,变形区的应变场分布与有限元结果吻合良好,有限元结果可靠。有限元结果表明,通过改变试样的缺口倾角,可以定量控制应力三轴度的大小,并且主应变方向与缺口倾角方向一致。在变形区Y方向发生压缩剪切的平面应变,同时试样边缘位置相对于中心位置具有更低的Lode角参数,具有双向压缩加载特征,使得静水压力增大,应力三轴度进一步降低至-0.823。

纯应力主轴旋转下固有各向异性砂土力学特性

【目的】进一步揭示固有各向异性和偏应力q对砂土力学特性的影响,深化对土应力方向依赖性的认识。【方法】利用新型制样装置制备具有固有各向异性的砂土空心圆柱试样,结合空心圆柱扭剪仪,开展一系列不同沉积面倾角a3和q条件下的不排水纯应力主轴旋转试验。【结果】在纯应力主轴旋转条件下,砂土临界周数随着a3和q的改变而改变,其数值最大可相差9倍;孔压前期累积速率也与a3和q有关,但中期稳定后的孔压数值受两者的影响较小;随着a3和q增大,剪应变累积速度加快,滞回圈面积及倾角也会发生变化。【结论】砂土的应变发展规律、孔压变化、剪应力-剪应变关系等动力学特性均与固有各向异性和q密切相关,且q的改变也会引起固有各向异性与动力学特性之间关系的变化。

2D-C/SiC复合材料的面内剪切本构模型

为了表征2D-C/SiC复合材料的面内剪切行为,考虑基体开裂、界面脱粘、纤维桥连弯曲等损伤机制,提出宏细观两尺度下的含损伤体元模型;引入热失配应力的影响,在分别表征卸载弹性应变和残余应变的基础上,建立材料的温度相关面内剪切本构模型。开展室温单调加载和加卸载面内剪切实验,发现残余应变和弹性应变均随剪应力的增大逐渐增大,而卸载模量随剪应力的增大持续减小。将模型用于2D-C/SiC复合材料剪切行为的模拟,结果表明:模型对于弹性应变、残余应变、卸载模量和整体应力-应变曲线的预测值均与实验数据吻合,验证了分析模型的合理性与准确性;在此基础上,给出2D-C/SiC复合材料在不同温度下的面内剪切应力-应变关系曲线,为热结构设计提供参考。

用Westergaard应力函数求解Ⅰ-Ⅱ复合型平面裂纹问题的研讨

直接获得Ⅰ-Ⅱ复合型平面裂纹问题裂纹尖端区域的应力场是一个比较复杂的问题,在此应用Westergaard应力函数求解Ⅰ-Ⅱ复合型平面裂纹问题,导出了裂纹尖端区域应力分量的表达式。该方法推导过程简单,物理概念清晰,其结果与一般断裂力学教材和文献中的结果一致。同时,应用叠加原理将裂纹面上的作用力转化为裂纹外边界的受力,给出了解决裂纹面上有作用力的Ⅰ-Ⅱ复合型平面裂纹问题的解题方法。

某大跨度异形板的结构设计与分析

以广州某住宅楼大跨度异形板为例,针对大跨度异形板及周边剪力墙容易出现裂缝的问题,通过强度设计、挠度裂缝分析、温度应力分析、舒适度分析、剪力墙平面外强度分析等设计方法,提出防止出现裂缝问题的措施在于大跨度异形板不仅要加强构造,还应在计算中同时满足强度计、裂缝计算、温度应力计算、舒适度计算、剪力墙平面外强度计算,以此满足结构安全和使用舒适度要求。

平面应变下原状黄土的剪切带研究

针对黄土地区工程建设中的平面应变问题,使用改进的西安理工大学真三轴仪进行了不同侧向固结压力、不同含水率下原状黄土的平面应变剪切试验,得出了剪切破坏时剪切带倾角试验值,根据应力-应变关系曲线求出了剪切带倾角的Mohr-Coulomb、Roscoe理论解,分析了相应控制因素下原状黄土强度、剪切带破坏模式与倾角的变化。结果表明:应力-应变曲线随含水率、侧向固结压力的增大从原生软化型向次生硬化型转变;剪切带破坏模式随侧向固结压力的增大依次呈现单一剪切带、锥型剪切带和X型剪切带;随着含水率的增大,黏聚力、内摩擦角减小导致Mohr-Coulomb剪切带倾角减小,剪胀作用增强导致Roscoe剪切带倾角增大;随侧向固结压力增大,动内摩擦角增大及剪胀作用增强,导致Mohr-Coulomb、Roscoe剪切带倾角增大。

常法向刚度条件下人工结构面剪切力学特性及损伤演化规律试验研究

为研究起伏角和法向刚度对结构面剪切力学特性的影响,利用自主研发的煤岩剪切-渗流耦合试验系统,开展了常法向刚度(CNS)条件下人工结构面的直剪试验。结果表明:当起伏角为15°和30°时,剪切应力呈现周期性震荡衰减趋势,在剪切结束时,随着法向刚度的增加,峰值剪切应力的降低量分别是1.78、1.42、1.36和1.27 MPa,逐渐减小。当起伏角为45°时,在剪切应力达到峰值后逐渐趋于残余强度;法向位移演化和剪切应力具有一一对应关系。随着起伏角的增加,剪切刚度逐渐增加。随着法向刚度的增加,起伏角15°和45°结构面的峰值剪切应力基本上线性增加;当起伏角为30°时,峰值剪切应力呈现出分段函数的特征,但是峰值剪胀角却逐渐降低。通过分析剪切前后结构面的质量损失、碎屑粒径占比和三维形貌参数演化得到结构面的破坏模式,当起伏角为15°和45°时,破坏模式较为单一,分别为磨损破坏和切齿破坏;当起伏角为30°时,其破坏模式对试验条件的依赖性较强较为复杂,主要为齿尖剪断破坏和全切齿破坏。通过将结构面三维空间点云数据和对应剪切位移处的法向位移值相结合的方法,得到特定剪切位移处的结构面隙宽演化云图,从而分析结构面在剪切过程中的动态演化过程,得到其破坏机理。

纯水系统平面O形密封圈密封性能仿真分析

针对纯水系统平面O形密封存在的失效问题,从平面密封结构出发,研究了影响密封间隙大小的主要因素,给出了介质压力和螺栓预紧力与结合面间隙的关系,并以某纯水支架卸载式三通块的平面密封为例,基于ABAQUS建立了平面O形密封的有限元仿真模型,分析了密封间隙和介质压力对密封主应力、接触应力及剪切应力等密封性能的影响规律。仿真结果表明:当平面O形密封的螺栓负载力大于预紧力时,将会在结合面产生间隙,且间隙随预紧力和工作压力的增大而变大;平面O形密封的等效主应力、上下接触应力随结合面间隙的增大而减小;密封间隙处的剪切应力大于材料的抗剪强度是出现间隙咬伤的主要原因,且间隙越大极限挤出压力越小,密封越容易被挤出而损坏。

基于双剪统一强度理论的挡土墙土压力计算

在工程实践中采用未考虑中间主应力对强度影响的经典的朗肯土压力理论来对挡土墙进行支护设计时往往存在误差较大的问题。文章基于双剪统一强度理论,将平面应变条件下的强度准则引入挡土墙土压力计算中,推导了基于双剪统一强度理论的挡土墙主动以及被动土压力计算新解。分析结果表明:中间主应力系数b对挡土墙的主动以及被动土压力值均有较大的影响,随着b值的增大,挡土墙主动土压力减小,墙后填土拉张区开裂深度增大,挡土墙被动土压力增大。因此,在工程应用中若能合理地考虑中间主应力对挡土墙土压力的影响,则会产生一定的经济效益。