Three-dimensional constraint-based failure assessment diagrams

Abstract

Current failure assessment diagrams codified in structural integrity assessment standards have been developed to consider in-plane constraint effects through K/J-T or J-Q approaches but neglect the effect of thickness on fracture toughness. Recent developments in the effect of thickness on fracture toughness have demonstrated a unique approach to unifying in-plane and out-of-plane constraint loss through a method proposed as J-Δσ. This method demonstrates that crack tip constraint loss in fully constrained and unconstrained geometries can be described by the secondary parameters T or Q and Δσ. Both secondary terms were based on the change of maximum normal stress from the fully constrained field within the micro-separation distance ahead of a crack front. The present work defined an approach to incorporate in-plane and out-of-plane constraint loss in failure assessment diagrams. The developed approach was successfully applied to a set of established experimental data and demonstrate a competent method for failure assessment diagrams through three-dimensional constraint-based fracture mechanics.