Fracture toughness in the evaluation of the propagation of a brittle crack in welded structures at low temperatures

摘要

The main criteria for the evaluation of the cold strength of steels and welded joints in steels in dynamic loading is the specific energy of fracture a_c~d. of a specimen with a crack (RD 50-344-82, GOST 9454-78 standard) and the stress intensity factors (SIF) K_(1c)~d, K_c~d, and in specimens with U-and V-shaped stress concentrators, it is KCU, KCV, KCU_i;, KCV_i, KCU_p and KCV_P. The decrease of the test temperature of the specimens for the same values of the energy of impact loading results in a decrease of the brittle crack propagation resistance of the materials and, consequently, in an increase of the rate of crack propagation. The stress intensity factors K_(1c)~d and K_c~d are the criteria of fracture toughness which determine the cracking resistance of the material at the moment of the start of crack propagation in dynamic (impact) loading of the specimen and cannot be used in the analysis of the limiting values of SIF K_(ld) in the presence of a propagating brittle crack. These characteristics are determined using the force-time or force-deflection impact loading diagrams~(1-3).