MICRO MECHANICAL ANALYSIS OF 3-D WOVEN COMPOSITES

A micro mechanical model is carried out to predict micro stresses and macro elastic properties of 3-D woven composites. A unit cell is composed of two phases. One is fiber yarn and the other is resin or fiber yarn in transverse. The additional shearing introduced by bending of fiber yarn is considered. The method to determine the microstructure is also discussed. This model is applied to the analysis of a 3-D woven graphite/epoxy composite. Micro stresses of the cell are studied, and then macro modulus is obtained by employing the average method. The predictions agree well with experimental results.

A modified maximum tangential tensile stress criterion for three-dimensional crack propagation

The three-dimensional （3D） crack propagation is a hot issue in rock mechanics. To properly simulate 3D crack propagation, a modified maximum tangential tensile stress criterion is proposed. In this modified criterion, it is supposed that cracks propagate only at crack front in the principal normal plane. The tangential tensile stress at crack front in the principal normal plane in local coordinates is employed to determine crack propagation, which is calculated through coordinate transformation from global to local coordinates. New cracks will propagate when the maximum tangential tensile stress at crack front in the principal normal plane reaches the tensile strength of rock-like materials. Compared with the previous crack propagation criteria, the modified crack propagation criterion is helpful in calculating 3D crack stress intensity factor, and can overcome the limitations of propagation step determined by individual experiences in previous studies. Finally, the 3D crack propagation process is traced by element-free Galerkin method. The numerical results agree well with the experimental ones for a frozen resin sample with prefabricated 3D cracks.

三维无单元伽辽金法及其在拱坝分析中的应用

本文介绍了三维无单元伽辽金法的基本理论,并将其应用于拱坝结构分析中,基于变分原理推导出三维线弹性无单元伽辽金法的整体平衡方程。为了处理实际水利工程中断层、宏观裂纹等不连续情况,采用可视准则处理不连续面对积分点影响域的影响,同时考虑不连续面两表面相互作用对整体平衡方程的贡献。编制了三维无单元法计算程序并用以分析拉西瓦水电工程拱坝-地基系统模型,结果表明,其反映了拱坝在水荷载作用下的位移分布规律。