A STUDY OF STATIONARY CRACK-TIP DEFORMATION FIELDS IN THIN SHEETS BY COMPUTER VISION

The in-plane deformation fields near a stationary crack tip for thin, single edge-notched (SEN) specimens, made from Plexiglas, 3003 aluminum alloy and 304 stainless steel, have been successfully obtained by using computer vision. Results from the study indicate that (a) in-plane deformations ranging from elastic to fully plastic can be obtained accurately by the method, (b) for U, epsilon(xx) and epsilon(xy) the size of the HRR dominant zone is much smaller than for V and epsilon(yy), respectively. Since these results are in agreement with recent analytical work, suggesting that higher order terms will be needed to accurately predict trends in the data, it is clear that the region where the first term in the asymptotic solution is dominant is dependent on the component of the deformation field being studied, (c) the HRR solution can be used to quantify epsilon(yy) only in regions where the plastic strains strongly dominate the elastic strain components (i.e., when \epsilon(yy)el/epsilon(yy)pl\ < .03 - .05); for V, the HRR zone appears to extend somewhat beyond this region, (d) the displacement component U does not have the HRR singularity anywhere within the measurement region for either 3003 aluminum or 304 SS. However, the displacement component V agrees with the HRR slope up to the plastic-zone boundary in 3003 aluminum (5 J/sigma0 < r < 25 J/sigma0) and over most of the region where measurements were obtained (J/sigma0 < r < 8 J/sigma0) in 304 SS and (e) the effects of end conditions must be included in any finite-element model of typical SEN specimen geometries to accurately calculate the J integral and the crack-tip fields.