Modeling thermal fatigue damage in metal-matrix composites

Abstract

Damage in the form of reduction in tensile residual strength due to combinations of thermal fatigue and time of exposure to maximum temperature is modeled using linear life-fraction modeling with the addition of an interaction term between cyclic and time-dependent contributions. Data from titanium alloys reinforced with SiC fibers involving thermal cycling, thermal cycles with hold times at maximum temperature, and long-term exposure at high temperature are used to determine model constants. A better representation of data is achieved by treating damage accumulation due to cyclic and hold-time effects as nonlinear functions of cycles and hold time, respectively, using power-law forms. Hold-time effects are found to accumulate damage in a highly nonlinear fashion, with the greatest amount of damage occurring for the shortest times. The differences between an interaction model and nonlinear model are discussed when applying them to fatigue-life prediction as well as in describing damage.