On single edge bend (SEB) specimens and spur gear models the fatigue crack propagtion rate at very low stress intnsity factor (SIF) was measured . The SIF for spur gear model was obtained by compliance measurements. The following expression which involves the threshold value of SIF was used to analyse the results .

da/dN= A [{ Ka/(1-R)r}β{Kat/(1-R)r}β] The present results beside it adds to the experimental evidence supporting the independence of growth rate on geometry of tested body, it extends the conclusion to cover the uninvistigated region at very low SIF.