铁电复合材料的力电耦合行为

对铁电复合材料力电耦合行为的研究进行综述．介绍了铁电复合材料的一些基本特点和线性压电有效性能的研究进展．阐述铁电复合材料中由于铁电相的铁电畴变与铁弹畴变以及基体相的弹性、粘弹性和介电弛豫性质所引起的铁电复合材料的非线性力电耦合行为．介绍了基于细观力学方法对铁电复合材料的本构关系进行研究的一些结果．     

近代塑性力学发展概况

经典塑性理论研究在50年代已经成熟,主要结果已总结在Hill的名著“塑性数学理论和Prager & Hodge的名著“理想塑性的固体理论”中。近15年来,非经典塑性理论突破了经典理论的先验限制,在下述六个方面有独特的发展:①由微小变形向有限变形发展,确立了有限塑性变形理论;②由宏观唯象理论向细观深度发展,确立了塑性细观力      

均匀化方法在粘弹性多层复合材料中的应用

主要研究了由各向同性线弹性加强体和各向同性线粘弹性基体组成的多层复合材料的问题,在已有的线弹性多层材料的均匀化方法的基础上,应用弹性一粘弹性对应原理,在Carson域中求解粘弹性多层材料的问题。通过Burgers模型表示线粘弹性基体材料,反演得到了多层材料的有效松弛模量和有效泊松比在时间域中的表达式,并且与实验结果和其他结果进行了比较。     

Constitutive models of ferroelectric composites with a viscoelastic and dielectric relaxation matrix (II)

Experimental analysis of ferroelectric composites with a viscoelastic and dielectric relaxation matrix is carried out, and the electromechanical coupling behavior of the ferroelectric composites is calculated by means of the constitutive model proposed in this paper. Comparisons between the experimental results and the calculations show that the constitutive model can reflect the electromechanical coupling behavior of the ferroelectric composites. The analysis indicates that the effect of viscoelasticity and dielectric relaxation of the matrix on the electromechanical coupling behavior of ferroelectric composites cannot be neglected.     

二维任意多边形有限单元

目前常用于单晶体材料的计算细观力学分析方法是将晶体细分成许多三角形或四边形有限元，对于多晶体材料，这方法的计算量之大将难于承受，实验观测表明，多晶体材料中除角点附近局部区域外每个晶体内部的变形、滑移基本上是绶慢变化的，因此可以将每个晶体简化为一个多边形有限单元，晶界简化为界面单元，使计算量大大减少，本文导出一类任意多边形等参有限元格式，并证明这类多边形单元中的任意两个都是相互协调的，无论其边数是否相等，算例表明任意多边形单元是有效可行的．     

Hierarchically Structured Materials for Bone Regeneration: Biomimetic Morphology,Micro-Mechanics and Properties

The contribution describes the development of a biocompatible nanocomposite material consisting of a resorbable polymeric matrix and osteoinductive nanoparticles that can be used to manufacture compact products, porous scaffolds, hybrid nanofibers, and alternating porous/compact structures. It is shown that the material has a good balance of stiffness, strength and toughness. The material supports osteoblast proliferation. Based on a modular design principle, several prototypes for hierarchical 3D constructs are proposed.     

A MODEL CONSIDERING HYDROSTATIC STRESS OF POROUS NITI SHAPE MEMORY ALLOY

Based on the micromechanical method and thermodynamic theory,a constitutive model for the macroscopic mechanical behavior of porous NiTi shape memory alloy is presented.The hydrostatic stress is considered for porous NiTi according to the transformation function of dense NiTi.The present model takes account of the tensile-compressive asymmetry of NiTi,and can degenerate to model dense material.Numerical calculations,which only need material parameters of dense NiTi,are conducted to investigate the nonlinear and hysteretic strain of porous NiTi,and the predicted results are in good agreement with the corresponding experiments.     

确定复合材料宏观屈服准则的细观力学方法

运用细观力学中的均匀化方法，分析了含周期性微结构复合材料的宏观屈服准则，并对Hill-Tsai准则进行了修正。从基于复合材料细观结构的代表性胞元入手，运用塑性极限理论中的机动分析以及有限元方法，计算了细观结构的极限载荷域。通过宏细观尺度对应关系，得到复合材料的宏观屈服准则。     

颗粒增强复合材料有效性能的三维数值分析

将细观力学和计算力学方法相结合用以确定复合材料中的局部和平均应力－应变场．对旋转体和非旋转体颗粒增强复合材料的有效模量进行了三维有限元数值计算，数值与实验结果对比表明，该方法是有效的、可靠的．分析了颗粒的排列分布、颗粒取向和颗粒的几何形状对有效模量的影响．数值结果表明，颗粒的排列对有效轴向弹性模量影响较大．颗粒的取向和颗粒的形状对有效性能的影响也是显著的     

The crack tip zone shielding effect for ductile particle reinforced brittle materials

The crack tip zone shielding effect for the ductile particle reinforced brittle materials is analyzed by using a micromechanics constitutive theory. The theory is developed here to determine the elastoplastic constitutive behavior of the composite. The elastoplastic particles, with isotropic or kinematical hardening, are uniformly dispersed in the brittle elastic matrix. The method proposed is based on the Mori-Tanaka's concept of average stress in the composite. The macroscopic yielding condition and the incremental stress strain relation of the composite during plastic deformation are explicity given in terms of the macroscopioc applied stress and the microstructural parameters of the composite such as the volume fraction and yield stress of ductile particles, elastic constants of the two phases, etc. Finally, the contribution of the plastic deformation in the particles near a crack tip to the toughening of the composite is evaluated. The project supported by National Natural Science Foundation of China