Effect of positive and negative stress ratio on a small time scale fatigue crack growth formulation

A previously developed small time scale fatigue crack growth model is improved and modified to predict fatigue crack growth (FCG) under positive and negative stress ratio. One of the significant phenomena of the crack opening stress under negative stress ratio is the residual tensile stress induced by the applied compressive load. A modified coefficient is introduced to determine the extent to which residual tensile stress impact the crack closure. A modified virtual crack-annealing model for crack closure is proposed and is shown to have satisfactory accuracy under both positive and negative stress ratio for a wide range of materials.