Fracture Criterion of a Mixed-Mode Crack (1st Report: A Study Based on Fracture of an Inclined Crack under Tensile Loading)

This paper purports to study the fracture criterion of a mixed-mode crack and to demonstrate that the criterion based on the CED (crack energy density) is available from completely elastic fracture to elastic-plastic fracture in a unified way. The CED in an arbitrary direction, ε_φ, is defined as the quantity which has the meaning of strain energy area density in the plane containing a crack front line without any restrictions on the constitutive equation. We may expect that a mixed-mode crack begins to grow in the direction φ where [formula omitted] (the mode I contribution of ε_φ) takes the maximum value, [formula omitted] when [formula omitted] reaches a critical value peculiar to a material (we call this criterion the [formula omitted] criterion). First, the applicability of this [formula omitted] criterion to elastic fracture is shown through the comparison between the results of the [formula omitted] criterion and the results of other criteria and experiments. Subsequently, fracture experiments of specimens of aluminum alloy with a crack inclined to the loading axis are carried out, and it is demonstrated that not only fractures with a relatively small yielding region but also fractures with a large yielding region can be explained by this [formula omitted] criterion.