A Novel Multiaxial Strain-Life Approach for Nickel-Base Superalloys Superalloys

Nickel-base superalloys (NBSAs) are a group of materials that are extensively used in high-temperature applications such as aero and industrial gas turbine applications. These alloys can endure high temperatures and stresses for extended periods, they also exhibit excellent fatigue life and corrosion-resistant properties. Multiaxial states of stress and strain are very common in engineered parts. Components such as blades, crankshafts, pressure vessels, welded joints, heavy construction equipment, and the like experience external loads in multiple axes. Multiaxial approaches have been introduced to give improved predictions of fatigue life under complex states compared to what can be attained with uniaxial methods alone. A novel multiaxial strain-based life approach is developed in this study. Coffin-Manson and Basquin equation is modified to include multiaxial strain range values. In this approach, all the modeling parameters are obtained from uniaxial low-cycle fatigue (LCF) experiments. Generic modeling parameters are provided to ease the material characterization process of newly developed NBSAs. These parameters are optimized by a MATLAB function to achieve accurate fit. The goal is to reduce number of complex and costly multiaxial fatigue experiments for the material characterization process of NBSAs. A yield criterion, developed by the authors, is utilized to obtain effective strain values and to capture multiaxial state of strain. This criterion is a modified version of Hill's yield approach. Certain parameters are added to include anisotropy of NBSA to the well-known Hill's approach. The multiaxial strain life approach is exercised and compared with experimental data from various single crystal (SX) NBSAs. A comprehensive database is created to include all the available multiaxial fatigue data on NBSAs in literature.