Crack Growth Rate Modeling of a Titanium-Aluminide Alloy Under Thermal-MechanicalCycling

摘要

In this study, a model is developed to predict crack growth rates in a titanium-aluminide alloy under thermal-mechanical fatigue (TMF). This TMF crack growth rate prediction model, which requires only isothermal data to define its parameters, is distinguished from earlier models in two ways. First, it accounts for mechanical-fatigue and environmental crack growth rate contributions while it also considers a retardation mechanism thought to be caused by creep blunting of the crack tip. This is the first study to account for such a retardation mechanism during TMF. The second uniqueness of the model is that its general form can account for cycle-dependent crack growth rate contributions that are temperature dependent. In addition, a series of isothermal-fatigue and hold-time tests are performed to generate the data base required for model parameters, and TMF tests are used to validate the modeling technique. The model predicts in-phase, as well as 180 deg and 270 deg out-of-phase crack growth rates extremely well, and underpredicts the 90 deg out-of-phase crack growth rates by a factor of two. Two other, more complex TMF cycles are studied, and the predicted crack growth rates correlate well with the experimental data.