Influence of viscoplasticity on the residual stress and strength of a titanium matrix composite after thermomechanical fatigue

Abstract

Abstract Modifications to the Bodner–Partom (B–P) constitutive equations provide improved flexibility in fitting a larger strain-rate range than previously available. Using the modified B–P equations, the importance of good matrix characterization becomes apparent for a SCS-6/Timetal®21S composites under thermomechanical and isothermal fatigue, as well as sustained loading. An interesting observation is that the residual stress after thermomechanical fatigue (TMF) can be significantly different than that found in the as-received composite. This phenomenon is cause by prestraining the fiber at high loads and temperatures during TMF. This phenomenon also provides an excellent opportunity to compare the predictive capabilities between the older and newer B–P models. When the maximum and minimum strains during TMF are obtained with the two models and compared to experimental measurements, the difference between the two models is minimal. However, inspection of the shifts in residual stress from the as-received condition shows significant differences between the older and newer B–P formulation. Lastly, pre-strained fibers caused by thermomechanical loading can cause a loss of room temperature tensile strength. To show this a rudimentary fiber failure model is defined. This model is used to show that the loading type strongly influences residual strength. The loss of residual strength is significantly more sensitive to loading type, rather than the viscoplastic characterization.