幂强化材料和超弹性材料组合球体中孔穴的动态生成

在简单加载条件下,研究幂强化材料和超弹性材料组合球体中的动态孔穴生成和增长问题.首先在有限变形动力学的框架下建立了相应的非线性数学模型,得到了应力的表达式,利用变量变换的方法求得了外加载荷和孔穴半径之间的一个精确的微分关系式.证明了当突加载荷超过其临界值时,球体内部有孔穴的突然生成,并随时间呈现非线性的周期振动.通过数值计算,分析了材料参数和球体的半径比对孔穴生成和增长的影响,并与相应的静态结果进行了比较.结果发现,惯性力的影响降低孔穴生成的临界载荷,而且材料的塑性对孔穴生成和增长有明显的影响.     

Natural frequencies of rotating functionally graded cylindrical shells

Love’s first approximation theory is used to analyze the natural frequencies of rotating functionally graded cylindrical shells.To verify the validity of the present method,the natural frequencies of the simply supported non-rotating isotropic cylindrical shell and the functionally graded cylindrical shell are compared with available published results.Good agreement is obtained.The effects of the power law index,the wave numbers along the x-and θ-directions,and the thickness-to-radius ratio on the natural frequencies of the simply supported rotating functionally graded cylindrical shell are investigated by several numerical examples.It is found that the fundamental frequencies of the backward waves increase with the increasing rotating speed,the fundamental frequencies of the forward waves decrease with the increasing rotating speed,and the forward and backward waves frequencies increase with the increasing thickness-to-radius ratio.     

自然复合材料的强韧化机理和仿生复合材料的研究

本文评述了一个新的研究方向─—自然复合材料强韧化的细观机理及其仿生复合材料的研究。着重考察了木、人骨、贝壳珍珠层、昆虫外骨骼及翅等自然复合材料的研究现状,基于这些研究,部分仿生材料已被设计和制造出来并达到商用程度．复合材料在细观层次的仿生,是将对复合材料及其结构设计产生潜在冲击的重要发展方向．      

A STUDY OF J-INTEGRAL OF THE ORTHOTROPIC COMPOSITE MATERIAL

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A general solution and the application of space axisymmetric problem in piezoelectric material

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爆轰波在阻尼管道中声吸收的实验研究

实验旨在研究气相爆轰波在阻尼管道 (管壁上衬有吸收材料 )中传播时的衰减现象。先是在光滑管壁的管道中产生稳定的具有胞格结构的爆轰波 ,然后使其通过专门设计的管壁上衬有吸收材料 (金属丝网或不锈钢纤维 )的阻尼段。利用高速摄影、压力传感器和烟迹技术等手段 ,记录和测试了阻尼段对几种混合气体爆轰波的传播速度、爆压及胞格结构产生的影响。实验分别在方管和圆管中进行。发现在某些条件下爆轰波可以被衰减成强爆燃。     

Crack propagation in a functionally graded plate under thermal shock

Summary Thermal cracking in a ceramic/metal functionally graded plate is discussed. When a functionally graded plate is cooled from high temperature, curved or straight crack paths are experimentally observed on the ceramic surface. One of the reasons that make the crack paths to differ are the thermal or mechanical conditions. In order to clarify the influence of these conditions on the crack path, the crack propagation is simulated using finite element method. Received 29 September 1998; accepted for publication 2 August 1999     

软铁磁材料平面裂纹问题的耦合场

由磁弹性问题的线性化理论导出磁场下平面软铁磁体问题的控制方程和复势解。利用复势解和奇异积分方程方法,对面内磁场和远场载荷作用下的含裂纹无限大软铁磁平面问题进行了求解,得到耦合场的解。并对不同磁力模型的结果和磁场与机械载荷共同作用下的裂尖应力强度因子进行了讨论。     

功能梯度矩形厚板的三维热弹性分析

直接从三维热弹性力学基本方程出发，通过引入两个位移函数和两个应力函数，导出了一个二阶的齐次状态方程和一个四阶的非齐次状态方程。分析中采用了层合近似模型，即将板划分成厚度足够小的若干薄层，从面可将每一层内的材料常数近似为常数。给出了任意厚度的四边简支横观各向同性功能梯度矩形板的热弹性分析，特别当板较薄时，与薄板理论进行了数值对比，发现两者结果吻合很好。最后研究了材料梯度指标对热弹性场的影响，结果显示梯度指标对热应力和位移都有着显著的作用：在不同的区间，梯度指标对它们有不同的影响；并且在同一区间，梯度指标对两者的影响程度也有所不同。     

Granular vortices: Identification,characterization and conditions for the localization of deformation

We relate the micromechanics of vortex evolution to that of force chain buckling and, on this basis, formulate the conditions for strain localization in a continuum model of dense granular media. Using the traditional bifurcation analysis of shear bands, we show that kinematic vortex fields are in fact solutions to the boundary value problem satisfying null boundary conditions. To establish an empirical basis for our study, we first develop a method to identify the location of the core and boundary of each vortex from a given displacement field in two dimensions. We then employ this method to characterize the residual deformation field (i.e., the deviation of particle motions from the continuum deformation) in a physical experiment and a discrete element simulation of dense granular samples submitted to biaxial compression. Vortices in the failure regime are essentially confined to the shear band. Primary vortices, the clear majority, rotate in the same direction as the shear band; secondary vortices, the so-called wakes, rotate in the opposite direction. Primary vortices align in spatial succession along the central axis of the band; wakes form next to the band boundaries, in between and beside two adjacent primary vortices. Force chain buckling, the governing mechanism for shear bands, is responsible for vortex formation in the failure regime. Vortex dynamics are consistent with stick-slip dynamics. From quiescent conditions of jamming or stick, vortical motions arise from force chain buckling and associated relative particle rotations and sliding; these in turn precipitate intermittent periods of unjamming or slip, evident in the attendant drops in stress ratio and bursts in both kinetic energy and local nonaffine deformation. A kinematic vortex field inside shear bands is proposed that is consistent with the equations of continuum mechanics and the underlying instability of force chain buckling: such a field is periodic with a repeating unit cell comprising a primary vortex at the center of the band, with two trailing wakes close next to the band boundaries.