EXPERIMENTAL AND NUMERICAL EVALUATION OF FATIGUE CRACK INITIATION AND PROPAGATION FOR IN738LC AT 850°C

摘要

Interrupted LCF-tests at 850°C for Inconel 738LC have been carried out and the specimens have been intensively examined by REM to quantify the evolution of fatigue damage. Surface crack nucleation at oxidized grain boundaries and coalescence of neighbouring flaws occured during the whole experiment. An anomalous fast single crack growth is observed just after nucleation, followed by a relative stagnation of the propagation in absence of coalescence. A statistical model is proposed that describes these phenomena. It leads to an integro-differential equation for the crack density f(c,n) after n cycles, similar to the Bolzmann equation which describes the collision of molecules in a dilute gas.