Automatic determination method of stress intensity factor utilizing digital image correlation and nonlinear least squares

A method for determining stress intensity factor automatically from displacement fields obtained by digital image correlation is proposed. In order to perform automatic and accurate evaluation, not only stress intensity factor but crack tip location and higher order terms in the series expansion of displacement fields are determined simultaneously in the present study. The nonlinear least-square approach based on Newton-Raphson method is applied to obtain all unknowns. The effectiveness of the method is demonstrated by applying the proposed method to mode I crack problem in a strip plate with a semi-infinite crack. Since stress intensity factor can be evaluated easily, simply and automatically by the technique with digital image correlation, it is expected that the proposed method can be applied to various fracture problems.