FATIGUE DAMAGE IN CROSS-PLY TITANIUM METAL-MATRIX COMPOSITES CONTAINING CENTER HOLES

The development of fatigue damage in four [0/90]s SCS-6/Ti-15-3 lamina tes containing center holes was investigated. A methodology to predict damage initiation based on an effective strain parameter was used to determine the stress levels and the number of cycles required for matr ix crack initiation. Damage progression was monitored at various stage s of fatigue loading. In general, a saturated state of damage consisti ng of matrix cracks and fiber-matrix debonding was obtained which redu ced the composite modulus. Matrix cracks were bridged by the 0-degrees fibers. The fatigue limit (stress causing catastrophic fracture of th e laminates) was also determined. The static and post-fatigue residual strengths were accurately predicted using a three dimensional elastic -plastic finite element analysis. The matrix damage that occurred duri ng fatigue loading significantly reduced the notched strength.