微粒填充流变材料界面开裂的局部临界应力及尺寸效应的理论分析

研究了以等轴粒子填充流变材料的边界开裂机理,采用能量准则导出了以界面能表示的界面开裂局部临界应力的简洁表达式。由于临界应力正比于１√α,从而可以非常方便地研究粒子开裂的尺寸效应,以碳酸钙微粒填充的聚丙烯复合材料为例进行了理论分析,通过比较界面开裂的能量准则和张应力准则得出结论：即使按照保守的方法估算,即在界面强度等于基体强度的条件下,只要粒径不超过０．２微米,若能量准则得到满足,则张应力准则也会得     

SHPB实验中端面摩擦效应研究

选取硅橡胶、聚氨酯泡沫、Comp.B炸药、PBX-HMX(97%)炸药以及6061-T6铝合金五种材料试样,对分离式霍普金森压杆（SHPB）实验技术中的端面摩擦效应进行了研究。实验结果表明,SHPB实验技术中的端面摩擦效应与材料的性质相关。另外,基于各向同性弹性理论,运用能量守恒法对SHPB实验中的端面摩擦效应进行了机理分析,研究表明,材料泊松比、端面摩擦系数、试样长径比、轴向应变是SHPB实验中影响端面摩擦效应的四个因素。     

Modeling the interfacial effect on the yield strength and flow stress of thin metal films on substrates

It is shown in this paper that interfacial effects have a profound impact on the scale-dependent yield strength and strain hardening rates (flow stress) of metallic thin films on elastic substrates. This is achieved by developing a higher-order strain gradient plasticity theory based on the principle of virtual power and the laws of thermodynamics. This theory enforces microscopic boundary conditions at interfaces which relate a microtraction stress to the interfacial energy at the interface. It is shown that the film bulk length scale controls the size effect if a rigid interface is assumed whereas the interfacial length scale dominates if a compliant interface is assumed.     

三维Cosserat连续体模型与微结构尺寸相关效应的有限元分析

分析了三维Cosserat连续体理论中的应力应变特征,推导了三维Cosserat连续体的有限元方程,基于ABAQUS计算软件提供的用户单元子程序(UEL)接口编写了弹性Cosserat连续体三维20节点有限元程序,并分析了微悬臂梁自由端的挠度问题和微杆扭转问题。通过与基于经典连续体理论的解析解及有限元数值计算结果进行比较,表明所发展的三维Cosserat连续体有限元能有效地模拟微结构尺寸相关效应问题,即随着微结构尺寸与材料内部长度参数的接近,基于Cosserat连续体有限元分析得到的微梁的挠度以及微杆的转角与经典连续体的解析解及有限元解相比越来越小;反之,Cosserat连续体有限元的计算结果与经典连续体的解析解及有限元数值解较为一致。     

An analysis of the modeling of stress and strain fields in a real microstructure using a hybrid method

The distribution of stress and strain fields in a micro-structural area of a particle reinforced composite is studied by a combination of experimental and numerical method (hybrid method). With the experimental values of displacements in a micro-region as the boundary loading condition, strain and stress fields inside the micro-region are calculated by the finite element method under two different kinds of modeling, namely, as plane stress and plane strain condition. The differences between the two kinds of modeling conditions as applied to micro-structural areas are discussed. Project Supported by the National Natural Science Foundation of China (19972046) and National Overseas Study Foundation.     

Influence of a thin isotropic coating on the edge effect zone in isotropic and transversely isotropic materials

The effect of a thin isotropic coating on the edge effect zone in a representative element of a coated material is examined. Isotropic and transversely isotropic materials are considered. The transversely isotropic material has the elastic properties of unidirectional glass-fiber-reinforced plastic. The decay of the edge effect in the directions perpendicular to the coating plane and to the plane of isotropy is studied. A boundary-value problem of elasticity for piecewise-homogeneouse orthotropic bodies and a quantitative edge effect decay criterion for normal stresses are used as a design model. The problem is solved using the finite-difference method and base schemes. The results of evaluation of the edge effect zone in homogeneous and inhomogeneous materials are presented. It is shown that the presence of a thin isotropic coating blocks the edge effect, that is, decreases the edge effect zone in both isotropic and transversely isotropic materials __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 12, pp. 61–67, December 2007.     

Lie group analysis for the effect of temperature-dependent fluid viscosity and thermophoresis particle deposition on free convective heat and mass transfer under variable stream conditions

This paper examines a steady two-dimensional flow of incompressible fluid over a vertical stretching sheet. The fluid viscosity is assumed to vary as a linear function of temperature. A scaling group of transformations is applied to the governing equa- tions. The system remains invariant due to some relations among the transformation parameters. After finding three absolute invariants, a third-order ordinary differential equation corresponding to the momentum equation and two second-order ordinary differential equations corresponding to energy and diffusion equations are derived. The equations along with the boundary conditions are solved numerically. It is found that the decrease in the temperature-dependent fluid viscosity makes the velocity decrease with the increasing distance of the stretching sheet. At a particular point of the sheet, the fluid velocity decreases but the temperature increases with the decreasing viscosity. The impact of the thermophoresis particle deposition plays an important role in the concentration boundary layer. The obtained results are presented graphically and discussed.     

初始纵横向荷载效应对薄板自振频率的影响分析The analysis for the effect of both initial in-plane and transverse loads on the natural frequency of plates

首先基于能量变分原理,给出了同时考虑初始纵向、横向荷载效应情况下板的应变能表达、动力平衡微分方程及单元刚度矩阵。再以动力平衡微分方程为基础,运用伽辽金法解得四种典型板同时考虑初始纵向、横向荷载效应的基频近似解,并运用瑞利法解得简支矩形板考虑初始纵向、横向荷载效应的前三阶频率近似解。然后相互验证了考虑初始纵向、横向荷载效应的板单元刚度矩阵和频率近似解的正确性,并进一步分析了初始纵向、横向荷载及相关因素对板自振频率的影响。结果表明,考虑初始纵向、横向荷载效应后,板的自振频率主要受初始纵向荷载、初始横向荷载、板的厚度及边界条件等因素的影响;初始纵向、横向荷载效应对板的基频影响明显于高阶频率;初始纵向、横向荷载对板的自振频率影响分别呈线性和抛物线规律。