ASSESSMENT OF J-INTEGRAL FOR 3-DIMENSIONAL SURFACE CRACK AT NOTCH ROOT

The contour J-integral values were calculated using the three-dimensio nal elastic-plastic finite element method for semielliptical surface c racks originated at notch roots under tensile loading. Then these were compared with the J-integral values calculated using the conventional equation we proposed in earlier papers, which we refer to as J hereaf ter. The difference between the two was quite small at the deepest poi nt A in the semielliptical surface crack, but was fairly large at the edge of a crack on the specimen surface, C. The conventional equation was modified by considering stress/strain gradients developed in the c ross section at the notch root. The J-integral value calculated using the proposed equation, J' was in quite good agreement with the contour J-integral value at both points, A and C in a semielliptical surface crack. The difference between the ratio J/J' and 1.0 increased with in crease in crack depth, depending upon the aspect ratio of the surface crack, magnitude of the applied stress and notch root radius. The para meter R-w was proposed, so that J/J' could be expressed by a unique cu rve as a function of R-w over quite wide ranges of notch root radius, surface-crack shape and magnitude of stress. The application limit of the simple J-integral estimation proposed earlier was assessed using t his curve. The crack growth rates obtained from fatigue tests of notch ed specimen were successfully plotted against J-integral range calcula ted using the modified conventional equation.