VARIATION OF CRACK-OPENING STRESSES IN 3-DIMENSIONS - FINITE THICKNESS PLATE

Crack growth and closure behavior of a center cracked finite thickness plate subjected to constant amplitude cyclic load is investigated by means of a three-dimensional elastic-plastic finite-element analysis. Results are obtained for initial half crack length c(i) to half plate thickness t ratios of c(i)/t = 3.981 and 1.465 which shall be referred to, respectively, as thin and thick plate. A constant amplitude load with R = S(min)/S(max) = 0.1 and S(max)/sigma-0 = 0.25 is applied, where S stands for the stress amplitude and sigma-0 the effective yield stress. Crack closure for the thinner plate is found to be largest at and near the free plate surface and to decrease toward the interior during the unloading portion of cyclic loading. The closure pattern stabilizes at the interior and exterior regions, respectively, for c(i)/t = 3.981 at 0.34S(max) and 0.56S(max) and for c(i)/t = 1.465 at 0.26S(max) and 0.46S(max). A load-reduced displacement technique was used to determine crack-opening stresses at specified locations in the plate from the displacements calculated after the 7th cycle (using unloading and reloading portions of cyclic loading). All locations were on the plate exterior surface and were located behind the crack tip and at the centerline of the crack. The opening stresses at the specified points as certain percentage of the maximum stress amplitude were obtained.