Automatic evaluation of mixed-mode stress intensity factors utilizing digital image correlation

A method for determining mixed-mode stress intensity factors from displacement fields obtained by digital image correlation is studied. To perform automatic evaluation, not only stress intensity factors but crack-tip location, higher-order terms in the series expansion of displacement fields and rigid-body displacement components are also determined simultaneously using nonlinear least squares based on the Newton-Raphson method. Experimental results show that the mixed-mode stress intensity factors are evaluated accurately from either radial or circumferential displacement components. As mixed-mode stress intensity factors can be evaluated easily, simply and automatically by the technique with digital image correlation and nonlinear least squares, it is expected that the proposed method can be applied to solve various fracture problems.