Abstract
This paper covers investigations of the effect of mean stresses normal to the crack plane on fatigue damage in uniaxial and torsional fatigue and of the effect of near yield stress overloads on fatigue damage in uniaxial and biaxial fatigue at various strain ratios. For uniaxial fatigue the results showed that the effective stress range at the fatigue limit was the same for all mean stresses. The fatigue limit stress range decreased linearly with increasing mean stress and crack opening stress until the point at which the crack opening stress fell below the minimum stress and the crack remained open. Then the fatigue limit stress range remained constant. A similar linear decrease of shear stress range, at a given fatigue life, with increasing mean stress normal to the crack was observed up to the mean stress at which the crack remained open. Again there was no further decrease in stress range beyond this point. Tests, in which overloads were inserted between smaller constant amplitude small cycles frequently enough to result in cracks that remained open at various biaxial strain ratios, resulted in strain-life curves identical to those obtained when high mean stresses were used to maintain open crack growth.
