Damage modeling of a transversely loaded titanium matrix composite under cyclic conditions

The life-limiting loading configuration of weakly bonded unidirectional titanium matrix composites is often transverse cyclic loading. Most fatigue tests under this loading configuration have been conducted at maximum stress levels above the monotonic proportional limit. However, the fatigue behavior at maximum stress levels below the monotonic proportional limit is often of interest, yet little work has been performed to identify this region on the fatigue life diagram. This investigation examined the behavior of a 16-ply SCS-9/Timetal 21S composite loaded transversely under generally low amplitude fatigue conditions. The fatigue limit under this loading configuration was found to be about one half the proportional limit. Residual strength tests were then conducted to determine the state of damage through measuring the change in stiffness using a number of unloading and reloading events. A damage mechanics methodology was demonstrated as a means to quantify the effects of the fatigue damage on the mechanical performance.