On the determination of J(IC) using the stretch zone width method

The stretch zone width (SZW = 1/2CTOD, the crack tip opening displacement) method for determining J(IC) involves fewer specimens and lesser size restr ictions compared to the conventional J-R curve method. However, the accurac y of the SZW-based procedure depends on each term of the J-CTOD relationshi p, i.e., J(IC) = m . sigma . CTODC. This paper presents a numerical investi gation 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 (sigma(o)/E), power law strain-hardening exponent (n), and different measures of stress (sigma in the J-CTOD relationship). This work brings ou t the importance of the correct choice of the stress measure, and the one s uggested here is the integral average of the flow stress [sigma* = integral (0)(epsilon)* sigma d epsilon/integral(0)(epsilon)* d epsilon]. effective C TOD approach is numerically validated where a sharp fatigue precrack of fra cture specimens can be substituted by one with a finite notch root radius w ithout loss of accuracy in J(IC).