Fracture Strength of PCS- SiC Fibers Extracted from Metal Matrix Composite : Effects of Surface Defects and a New Evalution Method

Abstract

The objectives of this study are to provide an evaluation model of fracture strength for reinforcing fibers and to apply this model to PCS-SiC fiber reinforced composite wires with variations of aluminum alloys as matrices. In the case of high strength composite materials, surface flaws or defects of fibers dominate fracture strength of reinforcing fibers and hence composites. A new model, where fracture strength is evaluated through surface defect density, is proposed as a method of statistical analysis. Mechanical property changes of PCS-SiC fibers during fabrication of Al, Al-Ni and Al-Si matrix composite wires are analyzed by this model. As the first part, fracture toughness of PCS-SiC fibers is derived using the size of "mirror" on fracture surfaces and the obtained value of 1.0 MPam^1/2 is applied to the evaluation model. In SiC/Al, the density of surface defects with the sizes from 90 nm to 130 nm increases. The effect of Ni addition to Al is found to suppress the increment of the surface defect density in the same range, whereas Si addition rather degrades the property comparing with the pure Al matrix. These results are consistent to the results of composite wires and prove the applicability of this model to these prroblems.