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

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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.