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A thermal fatigue test was designed and executed based on heating and cooling of a local spot in a thin titanium matrix composite (TMC) sheet by quartz lamps. This approach offers two features not offered by the load-controlled testing of standard coupons: (1) the stress state is biaxial instead of uniaxial, and (2) the mean stress is primarly compressive instead of tensile. A test rig was constructed to subject a small spot in the center of a 51-by 51-mm sheet of TMC to alternate heating and cooling between room temperature (RT) and 615°C. A specimen of unidirectionally reinforced SCS-6/Ti-6-2-4-2 was subjected to cycling with intermittent inspection for damage. Minimal cracking was observed in this test even after 10 000 cycles. Load-controlled low cyclic fatigue (LCF) and thermomechanical fatigue (TMF) tests were also performed on this material. The observed life in the hot-spot test was significantly greater than uniaxial transverse tensile fatigue load-controlled data would suggest based on a thermal stress analysis of the test panel. However, it was in reasonably good agreement with longitudinal, uniaxial load-controlled out-of-phase TMF data.
titanium matrix composites, fatigue (materials), thermal fatigue, titanium matrix, silicon-carbide fibers, finite element analysis, scanning acoustic microscopy, titanium, life prediction, titanium alloys, modeling
Principal engineer, GE-Aircraft Engines, Cincinnati, OH