抄録
The effect of interaction between fatigue and creep damage on rupture life and crack growth has been investigated in SUS304 austenitic stainless steel at 500°C. The experimental results were compared with a linear superposition model or a competition model (a crack grows by following the process that provides faster growth) and examined by observation of fracture surface.
The sum of fatigue and creep damage fraction for rupture life was less than one at low frequencies and more than one at high frequencies. At high frequencies the crack growth rate was in agreement with that predicted from both models in the early stage of crack growth, but the models overestimated the crack growth rate in the late stage. At low frequencies the crack growth rate coincided with that estimated from the models in the late stage of crack growth, but the models underestimated the crack growth rate in the early stage. It was revealed from observation of fractograph that there is a transition in fracture mode from transgranular to intergranular corresponding to a transition in crack growth rate. But the transition point in fracture mode or crack growth rate from transgranular fatigue failure to intergranular creep did not coincide with that estimated from the models. The disagreement between these models and the experimental data for rupture life, crack growth rate and fracture mode transition point at high frequencies may be explained by the decrease of crack growth rate due to creep strain recovery during unloading, but the reason for the disagreement at low frequencies is not clear at present.
