TENSION-COMPRESSION FATIGUE BEHAVIOR OF A UNIDIRECTIONAL TITANIUM-MATRIX COMPOSITE AT ELEVATED-TEMPERATURE

The fatigue behavior of a unidirectional metal-matrix composite, SCS-6 /Ti-15-3, has been investigated under tension-compression cycling at 4 27 degrees C. This behavior can be categorized into three regions on a fatigue life diagram. Region I, at higher stress levels, would be con trolled by fiber fracture. At intermediate stress levels, Region II in volved damage mechanisms which were dominated by matrix failure. Two d istinct damage mechanisms were observed in this region, region IIa inv olving little matrix cracking while region IIb consisted of considerab le matrix cracking. Region III was below the fatigue limit of the matr ix material resulting in fatigue lives longer than one million cycles. Tension-tension fatigue tests were also conducted at 427 degrees C to compare damage mechanisms and fatigue lives with those under tension- compression loading conditions. On a maximum stress or strain basis, t he fatigue life under fully-reversed, tension-compression cycling is l ess than that for tension-tension cycling. However, on the basis of st ress or strain range, the fatigue life under tension-tension cycling i s less than that for tension-compression cycling. (C) 1997 Elsevier Sc ience Limited.