Influence of the constraint effect on the fatigue crack growth rate in S355 J2 steel using digital image correlation

Displacement fields around the fatigue crack tip for a constant value of stress intensity factor (SIF) range were measured using digital image correlation (DIC) technique on the S355 J2 steel grade. The data obtained were resolved into the T-stress evaluation and quantification of its influence on the fatigue crack growth rate. The higher order terms of the Williams expansion (WE) were calculated as well. The displacements of a set of points outside of the plastic zone were selected for application of the over-deterministic method (ODM) to obtain several initial WE terms. The computed values of T-stress show good agreement with finite element analysis and literature. It was shown by collected experimental displacement, that the level of constraint influences the fatigue crack propagation rate.