FATIGUE AND RATCHETING INTERACTIONS

A review of experimental data from cyclic plasticity investigation performed on two structural steels was carried out to determine the influence of ratchet strain accumulation on fatigue life. Thin-walled tubular specimens, manufactured from a low-carbon steel (En3) and a low alloy steel(En19), were subjected to a range of constant twist amplitude cyclic plastic torsion, in combination with a range of constant axial loads. The results show that the En19 steel accumulates plastic axial strain at a much lower rate than the En3 steel. For both steels, the effect of increasing axial load is to reduce the fatigue life, with the fatigue lives for the En19 steel being higher than those for the En3 steel. Additionally, the slope of the Manson-Coffin plot remains virtually constant irrespective of the axial load in the case of the En19 steel. In the case of the En3 steel, however, for any given axial load, the Manson-Coffin plots show a change in slope, leading to shorter than expected fatigue lives at low plastic shear strain amplitudes.