(Dr. Richard Neu, advisor)

"Fretting Fatigue Crack Nucleation in Ti-6Al-4V"

Abstract

Fretting fatigue is the small amplitude oscillatory movement between contacting surfaces with one or more bodies undergoing fatigue loading.  Fatigue strength can be drastically reduced under fretting conditions and is responsible for numerous failures of engineering components such as Ti-6Al-4V gas turbine engine disks in military aircraft.

The aim of this experimental study is to provide controlled fretting fatigue conditions of a contact involving Ti-6Al-4V on Ti-6Al-4V that can be used to verify deformation and fatigue life behavior within the fretting process zone. Experimental methods for inducing fretting fatigue as well as exposing the subsurface damage were developed. A series of fretting fatigue tests were conducted varying the contact pressure, stress amplitude, and stress ratio for flat and cylindrical contact geometries.  Experimental analyses include surface and subsurface imagery for exposing the underlying microstructure in and around the fretting process zone.  The influence of contact pressure, stress amplitude, stress ratio, and contact geometry on the cycles to crack nucleation is studied along with the damage processes leading to such crack nucleation.