Study on the creep crack growth testing of metals based on direct and indirect methods

Abstract

Research on creep crack growth in defective materials or structures at high temperatures is essential for structural security evaluations. As the creep displacement rates of the specimens are estimated using the stress intensity factor K_I and plastic J-integral J_P, the traditional ASTM method is essentially an indirect method and some limitations have been discovered in previous studies. Based on the quasi-static load–displacement and creep displacement rate models for specimens with mode-I crack, an indirect method for creep crack growth testing is proposed according to the derived formula of elastic and plastic displacement rate and a direct method that obtains the creep crack growth rate of materials using only the crack length a. Furthermore, an iterative method for obtaining the real-time crack length through displacement–time curves was discussed by combining the indirect and direct methods. The proposed methods were verified using the results of finite element analysis (FEA) and experimental results for various materials. These results show that the direct method for creep crack growth testing is simpler and more effective than the indirect method, and the results predicted by the new methods are consistent with those obtained using traditional and literature-based methods.