A study of ductile crack corrections for elastic-plastic fracture toughness tests

Abstract

This paper critically examines existing ductile crack growth (DCG) corrections for J-integral values calculated with the multi-specimen and elastic compliance approaches, as well as two novel/alternative DCG corrections. The benchmark is represented by the incremental DCG correction prescribed by ASTM E1820-23a for Elastic Compliance tests. Considering calculations performed at both end-of-test and intermediate conditions, most of the existing and proposed approaches tend to under-correct J values, by an amount proportional to the percent of initial cracked ligament. For one of the proposed novel approaches (Pseudo-Resistance Curve Procedure), a tendency to overcorrection was observed. Nevertheless, when values of critical toughness (JQ, JIc) and ductile crack resistance (expressed in terms of tearing modulus, TM) are considered, differences are smaller than the typical uncertainties associated with elastic–plastic fracture toughness test results. Therefore, it does not appear necessary to modify the DCG corrections currently prescribed in the two most widely used fracture toughness test standards (ASTM E1820 and ISO 12135).