High-Temperature Fatigue of a Hybrid Aluminum Metal Matrix Composite
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An aluminum metal matrix composite (MMC) brake drum was tested in fatigue at room temperature and extreme service temperatures. At room temperature, the hybrid composite did not fail and exceeded estimated vehicle service times. At higher temperatures (62 and 73 pct of the matrix eutectic), fatigue of a hybrid particle/fiber MMC exhibited failure consistent with matrix overloading. Overaging of the A356 matrix coupled with progressive fracture of the SiC particles combined to create the matrix overload condition. No evidence of macro-fatigue crack initiation or growth was observed, and the matrix–particle interface appeared strong with no debonding, visible matrix phases, or porosity. An effective medium model was constructed to test the hypothesis that matrix overloading was the probable failure mode. The measured particle fracture rate was fit using realistic values of the SiC Weibull strength and modulus, which in turn predicted cycles to failure within the range observed in fatigue testing.
This work was funded in part by Army SBIR contract W56HZV-09-C-0026 through GS Engineering, Inc. (Houghton, MI). At GS Engineering, Jim Vendlinski assisted with FEA modeling and Paul Fraley and Tom Wood provided technical assistance. Matt Kero and Charlie Janis at Century Inc. (Traverse City, MI) supplied composite materials and insight on brake dynamometer testing. Pat Quimby, Steve Forsell, and Owen Mills at Michigan Tech provided experimental assistance.
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