Date of Award

12-1991

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Department of Aeronautics and Astronautics

First Advisor

Shankar Mall, PhD

Abstract

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° and 270° out-of-phase crack growth rates extremely well, and underpredicts the 90° 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.

AFIT Designator

AFIT-DS-AA-91-3

DTIC Accession Number

ADA244119

Comments

The author's Vita page is omitted.

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