Effects of Prior Inelastic Strain and Stress Concentrations on Fatigue Crack Nucleation and Propagation Behavior in High Pressure Turbine Disc Materials

It is widely recognised that the application of prior inelastic strain can have a marked effect on fatigue performance. The importance of understanding these effects cannot be underestimated, since significant amounts of prestrain are often a byproduct of the processing route. It is also unclear how the type of applied prestrain affects the subsequent fatigue life. For example whether prestrain is applied as plastic deformation through tensile loading, or as creep strain, along with the temperature at which it is applied.

The current paper seeks to investigate the effects of prior inelastic strain through a series of targeted fatigue tests. In the case of specimens representing in-service stress concentration features, it is necessary to define the nature of the changes in fatigue life; particularly whether it is the crack nucleation life or subsequent propagation behavior which shows the most significant effect.  A combination of load controlled fatigue tests, in association with crack propagation tests, performed at a range of applied stresses and prestrains allows for conclusions to be drawn about the overall effects of prestrain on a high performance nickel superalloy.