Experimental characterization and numerical modeling of crack initiation in rhombus hole PMMA specimens under compression

Under compression, mode I cracking in the loading direction is observed in PMMA rhombus hole specimens. Except for specimens containing flaws, spontaneous initiation is observed experimentally with the abrupt nucleation of a crack at the rhombus V-notch tip. With increasing hole angle and size, the force for crack initiation decreases whereas the crack arrest length increases. Similar influences of size and angle are predicted numerically by 2D and 3D finite element modeling of crack initiation using the coupled criterion, which allows crack initiation surface, shape and loading level to be determined. Initiation force and crack length depend on the specimen geometry and on boundary conditions. Compared to the 3D case, 2D modeling provides similar estimates of the crack length in the specimen midplane and overestimates the initiation force. The 3D crack shapes predicted numerically are qualitatively similar to the crack shapes observed experimentally. A reasonable agreement between numerical predictions and experimental measurements of initiation force and crack length is found.