The shape of a strain-based failure assessment diagram

There have been a number of recent developments of strain-based fracture assessment approaches, including proposals by Budden [Engng Frac Mech 2006;73:537–52] for a strain-based failure assessment diagram (FAD) related to the conventional stress-based FAD. However, recent comparisons with finite element (FE) data have shown that this proposed strain-based FAD can be non-conservative in some cases, particularly for deeper cracks and materials with little strain-hardening capacity. Therefore, this paper re-examines the shape of the strain-based FAD, guided by these FE analyses and some theoretical analysis. On this basis, modified proposals for the shape of the strain-based FAD are given, including simplified and more detailed options in line with the options available for stress-based FADs in existing fitness-for-service procedures. The proposals are then illustrated by a worked example and by comparison with FE data, which demonstrate that the new proposals are generally conservative.

► The strain-based failure assessment diagram approach to fracture is developed.
► The new approach modifies earlier proposals by Budden.
► A new generic Option 1 strain-based failure assessment diagram is proposed.
► Validation based on finite element J data for plates and cylinders is presented.
► The new approach is generally conservative compared with the finite element data.