THE EFFECT OF REST PERIODS ON THE FATIGUE LIFE OF MEDIUM CARBON STEEL UNDER DIFFERENT FATIGUE LOADING

Abstract

The fatigue crack growth ( FGG ) behaviour of medium carbon steel alloy under different rest periods is investigated under room temperature and stress ratio R= -1 using replicationtechnique . This work examines the constant and variable amplitude torsional fatigue underdifferent time of rest periods . The short and long fatigue crack growth equations are obtained experimentally . The average grain size diameter is 0.277 mm which separates between short and long crack region. The main remarks can be drawn from this work are : The fatigue life of specimens is increase by rest periods under constant amplitude tests . The factor of increasing is about 1-12 . While this factor becomes 1.75 – 8.7 times the predicted life forvariable amplitude tests . Rest periods generate strain ageing which in terms increase the totalfatigue life .