Relation of ηpl and γpl with separation parameter (S) and their usefulness for fracture toughness evaluation

Abstract

Geometrical factor ηpl and γpl are required for fracture toughness evaluation in terms of JIC, JQ and J-R curve. Load separation method is said to be most accurate method to evaluate the ηpl. In this method, established relation between ηpl and separation parameter (S) as well as fitted function between S and b/W is used to obtain the relation between ηpl and b/W. In this paper, relations of ηpl and γpl with the S are derived. Based on the fact that the value of γpl cannot be negative, limit of exponent of power law function between S and b/W as well as second order derivative of polynomial functions between S and b/W are evaluated. Limitations of power law function and usefulness of polynomial functions are highlighted. Usefulness of the relationships are discussed for CCT and clamped SENT specimens. The problem with Ernst type equation to calculate Jpl for growing crack are also discussed for CCT.