Unified correlation of in-plane and out-of-plane constraints with cleavage fracture toughness

• Three constraint parameters Ap, Q and T were analyzed by finite element method.
• The Ap can characterize a wide range of in-plane and out-of-plane constraints.
• The Ap can be used to establish unified correlation of constraints with toughness.
• The unified correlation lines are independent on the selection of standard specimen.

Extensive three-dimensional finite element analyses have been conducted for a large amount of experimental specimens with a wide range of in-plane and out-of-plane constraints. The capability of the new constraint parameter Ap for establishing a unified correlation of in-plane and out-of-plane constraints with cleavage fracture toughness of a reactor vessel steel were comparatively investigated with the conventional constraint parameters Q and T-stress. The results show that the parameter Ap can characterize both in-plane and out-of-plane constraints and their interaction. Based on the parameter Ap, the unified correlation of a wide range of in-plane and out-of-plane constraints with cleavage fracture toughness of the steel has been obtained. In structural integrity analyses based on fracture mechanics incorporating constraint effects for improving accuracy, the unified correlation may be used to determine constraint-dependent or structurally relevant fracture toughness of specimens or cracked components with a wide range of in-plane and out-of-plane constraint levels.