Plastic η factor considering strength mismatch and crack location in narrow gap weldments

The fracture toughness for LBB analysis of piping is generally determined in terms of the J-integral according to ASTM E1820. The J-integral consists in the elastic component Jel and the plastic part Jpl. Experimental evaluation of Jpl requires the plastic η factor. The J-integral evaluation by ASTM method was developed, however, essentially for homogeneous material. The fracture toughness of a strength mismatch weld evaluated as per ASTM method can, thus, differ from its actual value. In this study, the plastic η factors of similar as well as dissimilar metal narrow gap weld are suggested considering the influence of weld strength mismatch, weld width, and crack location. The proposed plastic η factors are compared with detailed finite element results. Few fracture tests were performed to quantify the influence of weld strength mismatch on fracture toughness of low alloy steels using C(T) specimens.