混凝土断裂过程的力学模型与数值模拟

混凝土是一种典型的非均匀准脆性材料，其断裂过程是非常复杂的. 评述了混凝土断裂以及断裂过程研究的进展状况，主要总结了一些研究混凝 土断裂的宏观力学方法和模型，介绍了从混凝土的细观层次出发模拟其断裂 过程的数值模型.最后，简单介绍了作者用细观数值方法模拟混凝土宏观断 裂过程的研究成果.  

混凝土细观随机骨料结构与有限元网格剖分

在细观层次上，混凝土被认为是一种由粗骨料、水泥砂浆及二者间的粘结带所组成三相非均质复合材料。本文首先基于蒙特卡罗随机抽样原理，用“取和放”方法在计算机上产生形状、尺寸和骨料颗粒分布与真实混凝土相似的随机骨料结构，再使用有限元分析软件ANSYS对骨料区域及砂浆区域分别划分网格，并编程在骨料和砂浆之间生成三角形三结点可控制厚度粘结单元，从而使三相网格缝合为一个整体，为混凝土非线性有限元分析提供可靠的细观计算模型。最后利用建立的模型进行混凝土轴心受拉和轴心受压的仿真模拟，在细观层次研究的基础上揭示出混凝土的宏观力学性能。  

Shock-induced phase transformation and vortex instabilities in shock loaded titanium alloys

Spall-tests of four kinds of high-strength titanium alloys (VT-6, VT-14, VT-20 and VT-23) have been performed by using a two-channel velocity interferometer for recording free surface velocity profiles and a SEM-technique for microstructure investigations of post-shocked specimens. Screw rotational structures in the spall zone are thought to be responsible for the more effective shock-wave energy scattering during spallation. Free surface velocity profiles display forward and reverse phase transitions in the all alloys under investigation. The threshold stress for the forward and reverse phase transitions turns out to be practically independent of the chemical and phase compositions of specimens, and monotonously increases with strain rate. Received 7 February 1999 / Accepted 3 November 1999