Experimental Study on the Two-Parameter Crack Tip Field

摘要

J-integral values were determined directly from the measured orthogonaldisplacement fields surrounding a crack in 2024-0, 2024-T3, 2091-T3 and 5052-H32 aluminum alloy SEN and cruciform specimens of 0.8 mm thickness. These J-values were then used to compute the crack tip displacements associated with the HRR field. The second order displacement component in the two-parameter, J-T and the more general J-Q ductile fracture theories was obtained by subtracting the HRR displacement from the measured crack tip displacement. This second order displacement component in the direction parallel to the crack was an order larger than the corresponding component perpendicular to the crack as predicted by the J-Q theory but not by the J-T theory. The negative slope of the log-log plots of the two orthogonal, second order displacement components with respect to the radial distance, however, suggests a strain singularity higher than that of the HRR strain singularity. The basic postulate of the asymptotic ex of crack tip pansion stress is violated and thus neither the J-T nor the J-Q theory can be a valid criterion in elastic-plastic fracture mechanics. elastic-plastic fracture mechanics, J-integral, J-Q theory, J-T theory, HRR field, moire interferometry, crack tip displacements.