Factors affecting the agreement between unloading compliance method and normalization method

Unloading compliance method (UC) and normalization method (NM) are two of the most commonly used methods for determining the fracture toughness of steels. Since the NM has been recognized as the most practical method there is a need to evaluate its accuracy against the classic UC method. This paper intends to investigate the factors that affect the agreement between UC and NM, including material mechanical properties, specimen thickness, the ratio of initial crack length to width (a0/W), specimen configuration, final crack extension, side-groove and the standards used. Both the literature survey and experiments are conducted to produce data for comparison. Based on a thorough analysis of test results, it is found in the paper that the agreement between UC and NM can be greatly affected by material mechanical properties, the ratio of initial crack length to width and the specimen configuration whilst the specimen thickness, the final crack extension and the side-groove only slightly influence the agreement. NM is recommended for specimens with shallow initial crack length, i.e., small a0/W. The results presented in the paper can assist engineers and researchers with accurate use of the normalization method for determining fracture toughness of steels.