THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING
GEORGIA INSTITUTE OF TECHNOLOGY
Under the provisions of the regulations for the degree
DOCTOR OF PHILOSOPHY
on Monday December 10th, 2018
in MRDC 3515
will be held the
DISSERTATION PROPOSAL DEFENSE
"CHARACTERIZATION AND MODELING OF TWO DIMENSIONAL CRACK GROWTH IN GAS TURBINE MATERIALS"
Prof. William Johnson, Advisor, MSE/ME
Prof. Richard Neu, Advisor, MSE/ME
Prof. Arun Gokhale, MSE
Prof. Christopher Muhlstein, MSE
Prof. Olivier Pierron, ME
Most fatigue failures of components are caused by cracks originating on their surfaces. These can be caused by many common problems such as marks from machining, foreign object damage, manufacturing defects, or corrosion. For this reason, the fatigue crack growth of surface flaws has been a subject of study for decades and are of particular interest in very expensive, and critical hardware such as aircraft components. Cracks starting at surfaces will grow under fatigue loading conditions both along the surface and in the thickness directions of the component geometry. Eventually the fatigue crack will reach the back face of the material and transition to a corresponding through crack geometry. While the fatigue crack growth behavior of both the surface flaws individually, and complete through cracks are well understood, the process by which they transition from one to the other is not. This project seeks to bring greater clarity and understanding to the transition process by implementing a transition method in the Multi-Parameter Yield Zone – Thermomechanical Fatigue (MPYZ-TMF) model and code, based on careful consideration of boundary conditions, experimental data and finite element simulations.
Jet engine components experience additional complications due to the fact that they not only experience mechanical cyclic loading but also thermal cyclic loading. The effect of this Thermomechanical Fatigue (TMF) has also been a subject of a great amount of research due to the complex interactions between the two types of cyclic loading. The second portion of this project will take the model of surface flaws and study how TMF influences the growth and shape of the crack. This portion builds on the previous research by Andrew Radzicki who quantified and modeled the effects of TMF on Inconel 718 in through cracks.