Model prediction of fatigue crack propagation in metal alloys in laboratory air

A local energy criterion is applied to the problem of a quasi-static extension of a subcritical crack embedded in an elasto-plastic matrix. It extends the Griffith fracture criterion to include fatigue. The derived expression for the fatigue crack growth rate is approximated by:dcdN=0.041EY(ΔK1−ΔKth)211−(K1 max/K1c)2where ΔK1 is the stress intensity factor (SIF) range, K1 max is the maximum value of, K1, K1c is the fracture toughness, ΔKth is the threshold SIF, E is Youngʹs modulus, and Y is the yield strength. The new analytical model for fatigue crack growth governs the subcritical growth of the crack up to the point of gross instability. It is a continuous process that covers the growth rate from the threshold to failure, and it has the capability of predicting the behavior of full-scale structures from small-scale laboratory tests. An extensive amount of published fatigue data for a wide range of metals and metal alloys is used to validate the new analytical expression for crack growth rate. The agreement between the predictions of the new model and the experimental data is fair to excellent.