On the Determination of JIC Using the Stretch Zone Width Method

Abstract

Abstract The stretch zone width (SZW=1∕2CTOD, the crack tip opening displacement) method for determining JIC involves fewer specimens and lesser size restrictions compared to the con ventional J-R curve method. However, the accuracy of the SZW-based procedure depends on each term of the J-CTOD relationship, i.e., JIC=m∙σ∙CTODC. This paper presents a numerical investigation of the J-CTOD relationship, which has been carried out using a large-deformation finite element method (FEM). The slope of the blunting line (m) is computed for various combinations of yield strength-to-elastic modulus ratio (σo∕E), power law strain-hardening exponent (n), and different measures of stress (σ in the J-CTOD relationship). This work brings out the importance of the correct choice of the stress measure, and the one suggested here is the integral average of the flow stress [σ*=∫0ε*σdε/∫0ε*dε]. Also, an effective CTOD approach is numerically validated where a sharp fatigue precrack of fracture specimens can be substituted by one with a finite notch root radius without loss of accuracy in JIC.