A new function describing fatigue crack growth curves

Starting with general phenomenological considerations, a function describin g the initiation as well as the stable and unstable growth of fatigue crack s is derived. In comparison with many other functions assigned to the descr iption of fatigue crack growth curves, its merit lies in its compatibility with some currently used functions - in a stable growth region the general function turns into the Paris-Erdogan law and, if the initiation region is added, it turns into the modified Klesnil-Lukas relation which enables a be tter fit of some experimental data than the original one. In the stable and subcritical regions the general function can turn into the Forman relation or into others, if special parameter values are chosen. Each parameters of the new function has a strictly defined geometrical meaning as far as the curve shape is concerned. A successful application of the function and its simplified forms for fitting other authors' experimental results for fatigu e crack growth obtained from tests made with different metallic materials, is presented. Also the generalized form of the function for different cycle asymmetries is proposed and successfully verified. (C) 1999 Elsevier Scien ce Ltd. All rights reserved.