Evaluation of the effectiveness of constraint parameters Q and φ on the uniaxial and biaxial bending specimen

Abstract

Constraint has a significant effect on the materials’ fracture toughness. A loss of constraint can cause a higher fracture toughness. The standard test geometries such as C(T) specimens are designed to have high levels of constraint which ensures that only a lower bound level of toughness can be measured through them. To get a more accurate fracture toughness of low constraint level components, it is necessary to study an approach of quantifying the constraint level and evaluating the apparent fracture toughness caused by the change in constraint. Currently, widely accepted crack-tip constraint parameters are validated using specimens with uniaxial loading such as C(T) and SEN(B). However, a lot of industrial equipment experiences loading modes other than uniaxial. The multi-axiality has been considered an important effect in various standards. It can cause a change in constraint and further fracture toughness. In this paper, a series of uniaxial and biaxial bending experiments with BS1501-224 28B steel were conducted at low temperature. A large amount of fracture test data of C(T) and SEN(B) specimens were collected to support the study. The effectiveness of elastic-plastic constraint parameter Q and unified constraint parameter φ for this constraint change were investigated with a series of finite element analysis data. It is found that the parameter Q and the unified parameter φ can quantify the constraint variations in C(T) and SEN(B) specimens successfully but are not effective for uniaxial and biaxial bending specimens.