Investigation into Fretting Fatigue Under Cyclic Contact Load and in Conjunction with Plain Fatigue of Titanium Alloy; Master's thesis

摘要

Fretting fatigue is the surface damage that occurs at the interface between two components that are under going a small amplitude oscillatory movements. It results in a reduction of the material life comparing to the plain fatigue. Most of the previous works were accomplished under a constant applied contact load and a little effort has been done under a variable contact load, while none of these studies have taken the phase difference between the axial and the contact load. The primary goal of this study is to investigate the effect of phase difference between axial and contact loads on fretting fatigue behavior of Ti-6Al-4V alloy and to determine the behavior of this material under combination of fretting fatigue and plain fatigue. The frequency of both axial and contact loads was the same .i.e. 10 Hz. During the variable contact load condition; only the axial stress range and the phase angle were varying. Cracks were always found to initiate on the contact surface and near the trailing edge for all tests. The software program, ABAQUAS, was used in finite element analysis to determine the contact region state variables such as stress, strain, and displacement. The fatigue parameters; such as the stress range, effective stress, and modified shear stress range (MSSR) were analyzed to predict the fatigue life. The out of phase condition was found to increase the fatigue life of 20% to 30% in life with low cycles and up to 150% at life with high cycles. As the application ratio of plain fatigue to fretting fatigue increases the life will increase. The MSSR parameter was effective in predicting the fatigue life, crack initiation location, and crack initiation orientation.