The effect of frequency on the fretting fatigue behavior of 7075-T651 aluminum alloy in lab air and vacuum environments.

摘要

The emphasis of this dissertation was to investigate and report the effect frequency has on the fretting fatigue behavior of 7075-T651 aluminum alloy. Even though frequency can have a profound effect on corrosion fatigue and fretting wear which are two of the processes necessary to fretting fatigue, very little research has been to date on frequency effects on fretting fatigue.; The first task was to determine if a frequency effect does exist. This was accomplished by conducting non-interrupted fretting fatigue experiments within a group of four specimens at three different frequencies. To ascertain if the frequency effect had any reliance on fatigue stress, fretting fatigue tests were conducted at two different stress levels. An attempt was made not only to uncover a frequency effect, but also to determine if the effect is predominant in either the crack nucleation phase, crack propagation phase, or both. To separate the frequency effect from either the mechanical or chemical aspects of fretting fatigue, tests were conducted in both lab air and vacuum. The important conclusions reached were: (1) There was a strong possibility of a frequency effect on the cycles to failure at both stresses. (2) The type or size of fretting wear damage had no effect on the cycles to failure. (3) Removing the normal load and increasing the frequency affected the cycles to failure when compared to the noninterrupted fretting fatigue specimens. (4) A frequency effect did possibly exist in vacuum. It is not certain whether a fretting fatigue type contact in vacuum will ultimately result in a fretting fatigue failure. (5) Two crack nucleation mechanisms may exist. The mechanism that dominates depends on the frequency of the fatigue loading.