MIXED MODE CUMULATIVE FATIGUE DAMAGE

Document Type : Original Article

Authors

1 Lecturer,Mech.Equip.Dpt.,Military Technical College, Cairo, Egypt.

2 Lecturer,Mech.Eng.Dpt., Azhar University, Cairo, Egypt.

3 Professor, Mech.Eng.Dpt., Sheffield University, Sheffield, U.K.

Abstract

The present work attempts to understand early fatigue damage accumulation in a mechanical sense. The effect of changing the mode of load, application from torsion cycling to push-pull cycling and vise-versa, on the same specimen,during the course of its life was investigated. Torsion prior to push-pull and push-pull prior to torsion mixed mode cumulative damage tests in both low and high cycle fatigue regimes were conducted. The cumulative damage tests were carried out between two strain levels selected such that when applied individually and separately, in each mode, would give the same endurance. It was found that when torsion cycling had been applied first, a 'decrease in the residual life in push-pull was observed indicating a positive damage due to the prior torsion. On the otherhand, prior push-pull cycling caused an increase in the residual torsional fatige life, which reached a max. of 170% after a push-pull damage of 70%, in the high cycle fatigue regime.