MECHANICAL MODELING OF INHOMOGENEOUS MEDIA AND APPLICATION TO EVALUATION OF HEAT AFFECTED ZONE IN WELD JOINT STRUCTURE

为了建立评价非均匀材料力学行为的分析方法，对焊接接头材料热影响区的微观变形进行了研究。得到了以下结果1.在Mo.9Cr-1Mo钢的热影响区，我们观察到细晶区和粗晶区。发现细晶区的硬度较低，这与著名的Hall-Petch效应完全相反。这是由于HAZ产生过程中复杂的温度历史造成的，仍需在更微观的水平上测量几个晶粒度量级的形变。多晶材料的模型分析将Asaro和Needleman的晶体塑性模型引入到三维有限元方法中，提出了一种多晶模型。分析结果表明，在较大的晶粒度范围内，预测的应变变化较大。这一趋势与实验定性一致。用跨砖单元节理单元技术评价晶界滑移，预测晶界滑移。晶界的滑动加速了应变的变化。该方法适用于滑移引起小裂纹张开的高温变形分析。基于各向异性的自适应建模提出了一种考虑各向异性变化的本构模型。各向异性会随着周围环境的变化而改变方向。结果表明，该模型不仅适用于纤维增强材料，也适用于生物组织等生物组织中发生自组织同时改变非均匀性的其他材料。

In order to establish the analytical methodology to evaluate the mechanical behavior of inhomogeneous materials, microscopic deformation is investigated on a heat affected zone (HAZ) of weld joint material. The following results are obtained.1. Hradeness of heat affected zone In the heat affected zone of Mod.9Cr-1Mo steel, we observe fine grain region and coarse grain region. It is found that the hardness of fine grain region is lower than the other, which is completely opposite to the well-known Hall-Petch effect. This is caused by the complicated temperature history in the course of generation of HAZ.It is still necessary to measure the deformation in more microscopic level of several grain size order.2. Model analysis of polycrystalline material Introducing a crystal plasticity model by Asaro and Needleman into three-dimensional finite element method, a polycrystal model is proposed. As a result of analysis, it is shown that more variety in strain is predicted in larger grain size region. Such a tendency shows qualitative agreement with experiment.3. Evaluation of grain sliding By use of a joint element technique across the brick elements, sliding in grain boundary is predicted. And the sliding in grain boundary accelerates the variety in strain. This technique is applicable to the deformation analysis at high temperature, in which the slide causes small crack opening.4. Modeling of self-adaptation in terms of anisotropy A constitutive model taking account of the variation of anisotropy is proposed. The anisotropy changes its direction due to the surrounding circumstances. It is shown that the model is applicable not only to the fiber-reinforced materials but also to other materials such as biological tissues, in which self-organization takes place while changing inhomogeneity by themselves.