A new formula for estimating fatigue crack propagation rates

Based on the eigenequation of crack growth in metals, a new analytical expression for estimating fatigue crack propagation rates is proposed. It takes into account the volume effect of the plastic zone ahead of crack tips and utilizes the concept that crack growth is controlled by the high-strain area (HSA) at the very tip of the crack. Factors such as the fatigue threshold values, ΔK_th, the cyclic mechanical properties of materials, Young's modulus of elasticity, the stress intensity factor range, ΔK, and the stress ratio, R, have been incorporated in the proposed model. The comparison between the theoretical curve and the experimental results for some materials indicates that the formula is correct for the determination of a crack propagation rate for da/dN<10^-3 mm/cycle.