Application of modified normalization method for J-R curve determination using clamped SENT specimens with varying in-plane and out-of-plane constraints

Abstract

In the present work, the normalization (NM) method was used to obtain J integral resistance (J-R) curves based on clamped single edge notched tension (SENT) specimens. The SENT fracture toughness tests using API X80 pipeline steel were carried out for a series of crack depth to specimen width ratios (a/W) and thickness to specimen width ratios (B/W), corresponding to varying in-plane and out-of-plane constraint conditions. To validate the normalization method, the unloading compliance (UC) method was adopted to derive the J-R curves for those clamped SENT specimens. In particular, two NM methods (modified NM method and unmodified NM method) are discussed and compared, and the experimental results indicated that the J-R curves calculated by the modified NM method have a better accuracy. Then, to quantify the modified NM method, the J-R curves, power law curve fitting parameters and the tearing modulus obtained from two methods (UC method and modified NM method) are compared. The comparison shows that good agreements are achieved among those methods. Moreover, three-dimensional finite element method (FEM) with GTN constitutive model is also used to determine J-R curves based on clamped SENT specimens. It is demonstrated that the modified NM method is an effective alternative tool for determining J-R curves of X80 steel based on clamped SENT specimens with different a/W and B/W ratios.