Axial and Bending Fatigue of a Medium Carbon Steel Including Geometry and Residual Stress Effects 2009-01-0422

This paper discusses the effects of changes in specimen geometry, stress gradient, and residual stresses on fully-reversed constant amplitude uniaxial fatigue behavior of a medium carbon steel. Axial fatigue tests were performed on both flat and round specimens, while four-point rotating bending tests were performed only on round specimens. All the tests were performed using shot peened and unpeened flat and round samples, to investigate the effects of compressive residual stresses on fatigue behavior. The specimens in the rotating bending tests experienced longer life for a given stress amplitude than in the axial test. Shot-peening was found to be beneficial in the long life region, while in short life tests the shot-peened samples experienced a shorter life than the unpeened samples under both axial and bending test conditions. Specimen geometry had a minimal effect on fatigue life and the difference observed between the behavior of round and flat samples is thought to be due to slightly different hardness levels of the two specimen geometries. The data generated from the aforementioned tests and conditions and the effects observed and their implications on fatigue behavior and life predictions are analyzed and discussed in this paper.