Early Fatigue Damage Research Articles

Effect of the secondary slip system on early fatigue damage

A face-centered cubic polycrystal under cyclic loading is considered. It is shown that slip in the primary slip system causes the resolved shear stress in a second slip system to increase to the critical value and then this second slip system slides. Slip in this second slip system greatly increases the rate of the local plastic strain build-up in the primary slip system. Hence the occurrence of the second active slip system may greatly increase the rate of extrusion and intrusion commonly observed in face-centered cubic metals.

The influence of strain-hardening and grain size on early fatigue damage based on a micromechanics theory

E arly fatigue damage is assumed to correspond to the build-up of local plastic shear strain. The influence of strain-hardening and grain size on the early stage of fatigue damage of a polycrystal subjected to fluctuating stress is considered. The calculations are based on a micromechanics theory proposed recently by the authors. It is shown that the increase of the strain-hardening rate and/or the decrease of the grain size decreases the rate of early fatigue damage. In order to produce 100 per cent local plastic shear strain for a given number of loading cycles, the range of the alternating stress decreases with increasing amounts of mean stress. This result is shown to be rather insensitive to the rate of strain-hardening and is found to lie between the values predicted by Gerber's parabolic law and by the modified Goodman linear law for fatigue failure.