Crack propagation behaviour of the titanium alloy IMI 834 under high temperature creep-fatigue conditions and finite element analysis

In the present study the interaction of creep and fatigue at the titanium alloy IMI 834 under cycles with different time dependent and time independent parts was investigated, and, furtheron, how these cycles influenced the propagation behaviour of long cracks. The lest temperature was 600 degrees C. It was found that crack propagation behaviour was significantly influenced by the type of creep-fatigue cycles applied. A slow increase of load into tension direction within the creep-fatigue cycles had a most detrimental influence on propagation of long cracks. For an evaluation of the stress and strain distributions at the crack tip under pure fatigue and under creep-fatigue conditions a Finite Element (FE) analysis was performed. The results showed that the stresses, strains and the CTOD-values in the vicinity of the crack tip also develop in a different way depending on the type of creep-fatigue loading applied. All results of the present study indicated that crack propagation under creep-fatigue loading is a complex interaction of crack tip deformations and environmental influences.