PLANE-STRESS STABLE CRACK-GROWTH AND J-INTEGRAL HRR FIELD

Moire interferometry with line densities of 1200 and 40 lines per mm w as used to determine the two orthogonal displacements surrounding a st ably extending crack in a 2024-T3 aluminum alloy, single edge cracked specimen. The test protocol consisted of using the fine moire grating prior to and up to the onset of crack extension and the coarse moire: grating for the ensuing crack extension up to Delta a = 6 mm. The disp lacement fields were used to compute the J-integrals for various conto urs during crack tip blunting and crack extension. As expected, the fa r-field J-integral value prior to stable crack growth coincided with t he LEFM strain energy release rate G, and validated the experimental p rocedure. However, the J values obtained from the near tip contour inc reased slowly, while the far-field J values increased rapidly with inc reasing stable crack growth. The HRR displacement field was computed f rom the experimentally determined far-field J. The HRR displacement fi eld agreed with the measured displacement field prior to stable crack growth since J = G. However, the HRR horizontal displacement field pro gressively deviated from the measured values with crack extension.