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

The life-limiting loading configuration of weakly bonded unidirectional tit anium matrix composites is often transverse cyclic loading. Most fatigue te sts under this loading configuration have been conducted at maximum stress levels above the monotonic proportional limit. However, the fatigue behavio r 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 amp litude fatigue conditions. The fatigue limit under this loading configurati on was found to be about one half the proportional limit. Residual strength tests were then conducted to determine the state of damage through measuri ng the change in stiffness using a number of unloading and reloading events . A damage mechanics methodology was demonstrated as a means to quantify th e effects of the fatigue damage on the mechanical performance.