| An improved moire interferometry setup, which records both the vertical and horizontal displacements simultaneously, was constructed to study ductile crack initiation and stable crack growth in aluminum alloys under the influence of biaxial loading. Whole-field measurements were used to evaluate the crack opening displacement (COD), far and near-field J-integral values and the Hutchinson-Rice-Rosengren, HRR, fields. The behavior of crack growth under the influence of biaxial stress was evaluated by conducting crack propagation tests on cruciform specimens made of 2024-0, 2024-T3 and 5052-H32 aluminum alloys. Tests were conducted at various biaxial load ratios. Contour maps of u- and v-displacement fields were obtained by moire interferometry, using reference virtual gratings of 1200 lines/mm (30480 l/in).; A computer based data reduction scheme, which automatically reduces the whole-field displacement fields measured using moire interferometry to strain, stress and subsequently J-Integral within the confine of a constitutive relation for selected contours, was developed. The J-values associated with stable crack growth in biaxially loaded 2024-T3, 2024-0 and 5052-H32 aluminum, single edge notched cruciform specimens, were found to be path independent and increased with crack extension. The transient displacement fields at the onset of crack initiation and during crack extensions up to 5.6 mm were used to evaluate the J-resistance, J{dollar}sb{lcub}rm R{rcub}{dollar}, curves. J{dollar}sb{lcub}rm R{rcub}{dollar} curves were identical within the scatter of data for all three different biaxial load ratios.; Special attention was focused on the HRR fields under uniaxial and biaxial load conditions. The moire interferometry method was used to record the intensive plastic deformation near the stationary and running crack tip and to check the validity of the numerical results based on small-strain asymptotic analysis. The u- and v-displacement fields at points along a 45{dollar}spcirc{dollar} radial line at radial distances 1.2, 5 and 10 mm from the crack tip were compared with the corresponding linear elastic fracture mechanics, LEFM, and HRR displacement fields, both of which were computed using the measured J-values, with increasing load and the attendant stable crack growth. The v-displacement field exhibited the expected evolution from the LEFM to the HRR singularities with increasing load. The u-displacement field did not exhibit any HRR singularity at higher loads. |
