き裂近傍の応力・ひずみ場を用いたＪ積分の測定 画像処理の応用

Abstract

Currently, J-integral proposed by Rice is one of the most effective elastic-plastic fracture mechanics parameters. However, only a few experimental method, which restrict specimen's shape, have been developed for the evaluation of the J-integral. Some of them are Rice's formula for three point bend specimens, Merkle-Corten's formula for CT specimens and so on, which utilize a load vs. Load-point-displacement curve. The others are strain gauge methods, in which elastic strains around a crack are measured by many strain guages, and the J-integral is calculated by a contour integration technique.In this study, we propose a new measuring method of the J-integral for arbitrarily shaped specimens. In this method, the displacement field in an elastic-plastic region near a crack tip is measured by a computer picture processing technique. Then the strain field is calculated by differentiating the displacement field, and the corresponding stress field is calculated using the multi-axial stress-strain relation of the deformation theory of plasticity. Finally the J-integral is evaluated through a contour integration technique. Since the present method directly measures the displacement field near the crack tip and evaluates the J-integral in the similar fashion to the numerical analyses, it can be applied to arbitrarily shaped specimens.In this paper, after summarizing the displacement measurent process by the computer picture processing, the calculation method of the J-integral is described. Then the accuracy and applicability of the present method is discussed in detail by comparing it with the conventional procedure based on Merkle-Corten's formula in a tensile experiment of CT specimen.