Effects of specimen size and stress ratio on fatigue crack growth after a single tensile overload

Abstract

This paper investigates the effect of specimen size, stress ratio, and loading pattern on fatigue crack growth for centrally cracked low carbon steel specimens. Elastic-plastic calculations were conducted under cyclic loading based on FEM using the domain integral method. The computed fatigue lives were firstly verified against the experimental tests taken from the literature. The numerical calculations showed that thickness has no significant effect on crack growth at a given stress ratio under the constant amplitude loading pattern. While the thinner specimens revealed longer fatigue lives compared to the thicker specimens at a certain stress ratio due to the application of a single tensile overload. A remarkable reduction in fatigue lives with a clear acceleration in crack growth rates was noticed for specimens with a small ligament length-to-specimen width ratio. The retardation response due to the application of a single tensile overload depended on a particular combination of specimen size and stress ratio. The variation in the crack driving force due to the change in thickness and ligament length was investigated. The relation between the crack driving force and the local stress state ahead of the crack tip was also discussed.