A STUDY ON FATIGUE CRACK PROPAGATIONSUPERIMPOSING HIGH CYCLES ON LOW CYCLESFOR TURBINE MATERIALS

The crack propagation under combined fatigue superimposing high frequency vibration with lower amplitude on low cycles with higher amplitude and its fractographic features for GH36 alloy are studied. Experimental results show that the high cycle damage will be a main factor when the amplitude ratio of high cycle to low cycle is larger than 0.98. Then,the surface deformation just ahead of the crack tip is decreased,each wide striation consisting of a number of parallel sub-striations produced by vibration stress and the cyclic hardening are increased. In this case,assessing of the FCG rate is basically independent of the LCF damage.