Effects of Mechanical and Environmental Variables on Fatigue Crack Growth Rates in Steel. A Summary of Work Done at Canmet

Abstract

Abstract Fatigue crack growth rates (FCGR's) provide a basic input into fracture mechanics life analysis of large cyclically loaded structures, where life is determined by the growth of an initial defect to critical size for failure. The FCGR for a particular material is primarily a function of stress intensity factor range ∆K, but other factors such as mean stress (usually expressed in terms of stress ratio R), cyclic frequency and presence of aggressive environments can significantly alter growth rates.In the present paper the effects of stress ratio and frequency are examined in air and in liquid environments (represented by 3.5% NaCl water solution, distilled water and sour crude oil) on ×65 and ×70 line-pipe steels, and on HY 130 marine steel. The FCGR's were measured over the whole range of ∆K, i.e., from threshold to incipient failure. The stress ratio strongly affects the threshold and near threshold growth rates by about the same amount in both air and aggressive environments. Empirical relations...