Establishment of Unified Correlation of In-Plane and Out-of-Plane Constraints with Ductile Fracture Toughness of Steel

摘要

In this paper, the finite element method (FEM) based on GTN damage model was used to obtain ductile fracture toughness and investigate the establishment method of unified correlation of in-plane and out-of-plane constraints with ductile fracture toughness of steels. The unified constraint parameter A_p at different equivalent plastic strain (ε_p) isolines has been calculated and analyzed for SEN(B) specimens with a wide range of in-plane and out-of-plane constraints. The results show that the average A_p along the specimen thickness (A_(pave)) can well characterize a wide range of in-plane and out-of-plane constraints. The suitable ε_p isolines range for establishing the unified correlation between A_(pave) and ductile fracture toughness of the steel has been obtained. For the specimens with lower constraint, the higher ε_p values should be used. The results also show that the correlation line of J_C/J_(ref)-A_(pave)~(1/2) is independent of the selections of the suitable ε_p isolines and the reference specimen. This may bring convenience for the establishment and application of the J_C/J_(ref)-A_(pave)~(1/2) correlation lines. Using ductile fracture toughness data of a small number of specimens with different constraints (such as three specimens with different a/W) together with FEM calculations of the parameter A_p, the correlation line of J_C/J_(ref)-A_(pave)~(1/2) can be established. The correlation line may be used in structural integrity assessments incorporating both in-plane and out-of-plane constraints.