Tension-compression fatigue behavior of a unidirectional titanium-matrix composite at elevated temperature

Abstract

The fatigue behavior of a unidirectional metal-matrix composite, SCS-6/Ti-I5-3, has been investigated under tension-compression cycling at 427 °C. This behavior can be categorized into three regions on a fatigue life diagram. Region I, at higher stress levels, would be controlled by fiber fracture. At intermediate stress levels, Region II involved damage mechanisms which were dominated by matrix failure. Two distinct damage mechanisms were observed in this region, region IIa involving little matrix cracking while region IIb consisted of considerable matrix cracking. Region III was below the fatigue limit of the matrix material resulting in fatigue lives longer than one million cycles. Tension-tension fatigue tests were also conducted at 427 °C to compare damage mechanisms and fatigue lives with those under tension-compression loading conditions. On a maximum stress or strain basis, the fatigue life under fully-reversed, tension-compression cycling is less than that for tension-tension cycling. However, on the basis of stress or strain range, the fatigue life under tension-tension cycling is less than that for tension-compression cycling.