Abstract
This paper presents an experimental study to investigate the effect of phase difference between axial and contact loads for fretting fatigue behavior of Ti-6Al-4V alloy. The  amples were tested using a bi-axial servo-hydraulic test machine. The frequency of both axial and contact loads was kept constant at a value of 10 Hz. The applied axial stress
was varied between 56 MPa and 564 MPa and the contact load was varied between 2224 N and 4448 N. Four phase angles between axial and contact loads were selected: 0°, 60°, 90° and 105°. In all tests, cracks were found to initiate at the contact surface near the trailing edge. The coefficient of friction was found to be smaller in tests carried out at out- of-phase conditions compared to tests done under in-phase conditions. The crack initiation orientation for in-phase condition was similar to previous studies, however for the out of phase condition the crack initiation orientation deviated by 10°. For the in-phase condition, the fatigue life was almost the same as that for constant contact load which
agrees with previous studies. However, the out of phase condition has increased the fatigue life by about 30%. In addition, life was doubled at 105° phase angle in comparison to the in-phase loading.