PREDICTION OF CREEP CRACK GROWTH INCUBATION PERIODS

An incubation period is often observed prior to the onset of creep crack growth. This paper presents a procedure for estimating its duration from a knowledge only of the stress rupture properties and creep ductility of a material. Comparisons are made with experimental data on type 316L stainless steel at 600°C and a 1% CrMoV low alloy steel at 550°C. It is shown that good agreement is achieved when allowance for a build up of damage in a process zone at the crack tip during the early stages of cracking is incorporated into the analysis.