Analytical Services & Materials, Inc.

Problem: Crack mouth opening displacement (CMOD) was required for analysis validation of a 0.02 inch long part-through crack in a thin sheet aluminum material that was subjected to cyclic tensile and compressive yielding. The aluminum material was "sandwiched" between two thicker sheets to prevent buckling during the compression portion of the loading cycles. A small hole in the thicker sheets allowed for a 0.5 inch by 0.5 inch viewing area for the crack. Traditional contacting methods were too large to successfully extract the crack opening behavior.

Solution: The surface of the aluminum sheet was painted with a white base and black paint was misted on the surface to generate speckles that were about 0.001 inches in diameter. The VIC3D system was used to sample 50 images per cycle. The displacement at points 0.015 inches above and below the crack were extracted from the post-processed data and plotted as a function of the average stress across the crack plane. The load-displacement data was compared directly with the output from an elastic-plastic finite element analysis.