Failure Prediction of Curved Wide Plates Using the Strain-Based Failure Assessment Diagram With Correction for Constraint and Notch Radius

Abstract

The strain-based failure assessment diagram (SB-FAD) has been developed for predicting failure from flaws in components subjected to high plastic strains. In this paper, a combined numerical and experimental approach is used to apply the SB-FAD to predict failure from a series of API 5L grades X80 and X100 curved wide plate (CWP) specimens with shallow notches machined into the pipe girth weld. For the CWP specimens tested in this work, the SB-FAD in its unmodified form resulted in over-conservative predictions of failure. This is attributed to the SB-FAD assuming high constraint conditions and the presence of a sharp fatigue crack, whereas the CWP specimens tested in this work were low constraint and contained a shallow machined notch without fatigue cracks. A modification of the SB-FAD is then proposed to account for non-sharp defects loaded to high plastic strains under conditions of low constraint. The resulting predictions of the modified SB-FAD show significantly reduced conservatism compared to the unmodified SB-FAD.