A Fatigue-Crack Propagation Analysis Program and Its Application

Abstract

The theoretical models, calculation algorithms, and an application example of LBB-FATIGUE program are described. Based on the crack propagation analysis method of linear elastic fracture mechanics (LEFM), LBB-FATIGUE program is developed to calculate the propagation length versus the design-transient loads and operational time as well as the lifetime of a fatigue crack in austenite stainless steel pipes within the primary coolant environment of PWR or BWR plants or in the air (t > 100 °C). The main calculation models are as follows: (1) The influence of the primary coolant environment to the fatigue-crack growth rate(FCGR) is considered; (2) according to the superposition principle, the variation range of the total stress intensity factor $K_{I}$ is expressed as the sum of tension subpart $K_{I}^{t}$ and bending subpart $K_{I}^{b}$; (3) F functions given by Sander’s analysis for pure-tension load and pure-bending load are adopted; (4) the design-transient loads are a series of variable amplitude loads which are considered as an equal amplitude load alone, and expressed as variation range of tension force and bending moment; (5) Newton method or the chasing method is used to calculate the variation of the crack propagation length versus design-transient cyclic numbers. In the leak-before-break (LBB) analysis for the primary circuit of CPR1000 nuclear power plant (NPP), the propagation length and the lifetime of a postulated circumferential through-wall crack (TWC) in the sensitive fractural position under design-transient loads are calculated by LBB-FATIGUE program.