Influence of Contact Stresses on Crack-Tip Stress Field: A Multiparameter Approach Using Digital Photoelasticity

The interaction of stress fields between cracks or cracks with discontinuities like holes, etc., has been widely studied. Another crucial class of problems include cracks interacting with contact stresses but there has been no work to study them systematically. This study aims to understand the role of contact stress in influencing the crack-tip stress field which is essential for reliable estimation of stress intensity factors (SIFs) experimentally. The contact stress influence on crack-tip isochromatic features is initially discussed using an experimental result for a moderately-deep beam with a small crack. SIFs are evaluated using the over-deterministic nonlinear least squares method. The crack-contact stress interaction is then studied by a superposed crack-contact analytical solution. Photoelastic experiments are conducted for a cracked moderately-deep beam subjected to three-point bending. The SIFs evaluated using the multiparameter solution compare well with finite element predictions. Subsequently, multiple interaction configurations are experimentally examined in a cracked moderately-slender beam by varying the magnitude and position of the contact load relative to the crack. Even a small crack shows a noticeable change in isochromatics due to influence of contact stress and a two-parameter solution is inadequate here. A multiparameter crack-tip solution is observed to capture the isochromatic fringe field very effectively towards SIF evaluation. The changes in isochromatics at a crack-tip due to contact stresses are significant. A systematic analysis shows that with appropriate data collection, the multiparameter solution provides SIFs with very little uncertainty in the presence of contact stresses with varying complexities.