切欠底に存在する三次元表面き裂に対するJ積分評価

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The contour J-intergral values were calculated using the three/dimensional elastic-plastic finite element method for semielliptical surface cracks originating at notch roots under tensile loading. Then these were compared with the J-integral values calculated using the conventional equation that we proposed in earlier papers, which we refer to as J hereafter. The difference between the two was quite small at the deepest point A in the semielliptical surface crack, but was fairly large at the edge of a crack on the specimen surface, C. The convensional equation was modified by considering stress/strain gradients developed in the cross section at the notch root. The J-integral value, J'calculated using the proposed equation was in quite good agreement with the contour J-integral value at both points, A and C in a semielliptical surface crack. The ratio J/J'decreased with increase in crack depth, depending upon the aspect ratio of the surface crack,magnitude of the applied stress and notch root radius. The parameter R_w which was determined from F. E. M. calculation was proposed so that J/J'could be expressed by a unique curve as a functien of R_w over quite wide ranges of notch root radius, surface-crack shape, and magnitude of stress. The limitation for applying the simple J-integral estimation proposed earlier was determined using this curve. The crack growth rates obtained from fatigue test of notched specimen were successfully plotted against J-integral range calculated using the modified conventional equation.
1996-07-25

切欠底に存在する三次元表面き裂に対するJ積分評価

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