Extrapolation Techniques for Very Low Cycle Fatigue Behavior of a Ni-base Superalloy

A combination of extrapolation and estimation techniques from both prior and current studies has been explored with the goal of developing a method to accurately characterize high-stress amplitude low cycle fatigue of a material commonly used in gas turbine blades with the absence of such data. This paper describes innovative methods used to predict high-temperature fatigue of IN738LC, a dual-phase Ni-base superalloy. Three sets of experimental data at different temperatures are used to evaluate and examine the validity of extrapolation methods such as anchor points and hysteresis energy trends. High-stress amplitude data points approaching the ultimate strength of the material were added to pre-existing base data with limited plastic strain to achieve a full-range data set that could be used to test the legitimacy of the different prediction methods. Each method is evaluated at a number of temperatures.