Crack Tip Strain—A Comparison of Finite Element Method Calculations and Moiré Measurements

The moiré crack tip strain measurements made on double-edge-notched specimens loaded into the region of general yielding are compared with the finite element method (FEM) calculations. If the ratio of specimen thickness and the total net cross-sectional width, (W-2a)/t, is equal to or more than ten, the bulk of the strain measurements agree well with the results of the plane stress calculations except in the small area close to the crack tip. The crack tip region is stiffened by the triaxial state of stress, and the deformation within the stiffened zone is less than that calculated for the plane stress model. The region affected by the crack tip stiffening extends to a distance from the crack tip equal to specimen thickness. This crack tip stiffened zone is imbedded in the characteristic plane stress zone if (W-2a)/t is larger or equal to ten.