A Novel Unified Characterization Parameter of In‐plane and Out‐of‐plane Constraints Based on Critical CTOA

There is much controversy in using laboratory specimens to predict the fracture behavior of large industrial constructions because of their different constraints. Although several parameters have been proposed to characterize the constraint effect, there are still some limitations. To address this issue, a novel unified characterization parameter of constraint based on the critical crack tip opening angle (CTOA(C)) is defined. Firstly, the calibrated finite element technologies for simulation of static and dynamic crack are used to determine the equivalent plastic strain (epsilon(p)) distribution around the crack tip and the evolution history of CTOA for specimens with different in-plane and out-of-plane constraints, respectively. Secondly, the feasibility of the equivalent plastic strain at the crack tip when CTOA reaches its critical value to unified measure both in-plane and out-of-plane constraints is investigated. The results indicate that the area A(PEEQ) surrounded by the isoline of equivalent plastic strain epsilon(p) can describe both in-plane and out-of-plane constraints and the interaction between them. Finally, a novel constraint characterization parameter eta is defined. It is found that there is a linear relationship, which depends only on the material and regardless of the selection of the epsilon(p) isoline, between the normalized fracture toughness CTOA(C)/CTOA(ref) and eta(1/2). The work in this paper is expected to realize the matching of constraints between different laboratory specimens or industrial constructions.