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.