Experimental evaluation of crack shielding during fatigue crack growth using digital image correlation

In the current paper, a methodology for the evaluation of fatigue crack shielding using 2D digital image correlation (DIC) is proposed. The crack tip shielding has been evaluated from the analysis of the displacements field observed at the vicinity of a growing fatigue crack. The proposed methodology is based on the evaluation of the stress intensity factors calculated from displacement fields measured around the crack tip using DIC. A comparative study employing four different mathematical models describing the crack tip displacements field (namely Westergaard, Williams and Muskhelishvili equations and Christopher, James and Patterson model) has been performed. For this purpose, a set of fatigue tests on aluminium 2024-T3 compact tension specimens have been conducted at different R-ratios. Results obtained from DIC technique have been compared with those obtained using compliance-based methods. Results show a very good level of agreement illustrating the potential of the DIC technique for the analysis of crack shielding during fatigue crack growth.