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Fatigue Behavior of a Cross-Ply Metal Matrix Composite at Elevated Temperature Under Strain Controlled Mode.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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This research extends the existing knowledge of cross-ply metal matrix composites MMC to include fatigue behavior under strain-controlled fully reversed loading. This study investigated fatigue life, failure modes and damage mechanisms of the SCS-6Ti-15-3, O9O2s, MMC. The laminate was subjected to fully reversed fatigue at elevated temperature 427 deg C at various strain levels. Stress, strain and modulus data were analyzed to characterize the macro-mechanical behavior of the composite. Microscopy and fractography were accomplished to identify and characterize the damage mechanisms at the microscopic level. Failure modes varied according to the maximum applied strain level showing either mixed mode i.e. combination of both fiber and matrix dominated modes or matrix dominated fatigue failures. As expected, higher strain loadings resulted in more ductility of the matrix at failure, evidenced by fracture surface features. For testing of the same composite laminate, the fatigue life under strain controlled mode slightly increased, compared to its load-controlled mode counterpart, using the effective strain range comparison basis. However, the respective fatigue life curves converged in the high cycle region, suggesting that the matrix dominated failure mode produces equivalent predicted fatigue lives for both control modes.
APPROVED FOR PUBLIC RELEASE