L-286 Thermomechanical Fatigue An Introduction

The purpose of this report is to present an introduction to thermomechanical fatigue and how this applies to energetic materials.  This topic is seldom, if ever, treated in materials science textbooks. There is first a description of the generation of thermal stresses due to heating and cooling and how these relate to material properties.  The two considerations of crack initiation and crack propagation are reviewed and the relevant material properties and heat transfer conditions identified.  The time to maximum stress is noted for a flat plate, which is fit to an empirical equation. Time to maximum stress for energetic materials will be relatively long given the relatively low thermal diffusivity. This complicates the analysis when several temperature changes occur within this time span.  A few analytical methods for analysis of thermal fatigue are noted.  Damage accumulation rules, such as that by Coffin Manson, and more sophisticated models are reviewed.