The Hierarchy of Fatigue Mechanisms in the Long Lifetime Regime (Preprint)
Abstract
The primary factors governing the behavior in the long lifetime regime of turbine engine materials are discussed. These factors are based on a study of fatigue lifetime distributions and underlying mechanisms in a number of materials, including titanium alloys, nickel-base superalloys, and gamma TiAl based alloys. A hypothesis of fatigue variability is described, and appears to explain the various features of fatigue behavior seen in the HCF and VHCF regimes. Central to the hypothesis is the proposition that a hierarchy of fatigue deformation heterogeneities develop in a specimen upon fatigue loading, which presents a finite probability of almost instantaneous crack initiation (and therefore, a limiting lifetime) under any nominal microstructure and loading condition. A probabilistic calculation using computational microstructural volumes representing a duplex alpha+beta titanium alloy was conducted in order to elucidate the nature of the relationship between frequency of occurrence and complexity of crack-initiating microstructural arrangements. Calculations demonstrated a steeply declining trend of frequency with increasing complexity of the arrangement.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 2011
- Accession Number
- ADA553360
Entities
People
- C. J. Szczepanski
- Craig Przybyla
- James M. Larsen
- Sushant K. Jha
Organizations
- Air Force Research Laboratory