Micromechanical Modeling of Fiber/Matrix Interface Effects in Transversely Loaded SiC/Ti-6-4 Metal Matrix Composites

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Abstract

The transverse tensile behavior of a composite composed of unidirectional silicon-carbide fiber (Textron SCS-6) in a Ti-6AL-4V matrix is examined with emphasis on the effects of fiber-matrix interface strength. The residual stresses as a result of a mismatch in the coefficients of thermal expansion of silicon carbide and titanium are estimated analytically and compared with measurements made using X-ray diffraction techniques. Idealizing the composite as a regular rectangular array of fibers in an elasto-plastic matrix, the transverse tensile stress-strain behavior is predicted under the assumptions of an infinitely strong interface as well as an interface without tensile strength. These results are compared with experiments conducted at three different temperatures. The agreement between experiment and predictions based on an interface without tensile strength is extremely close. The modeled stress-strain curves predict a well-defined knee in the transverse tensile stress-strain curve associated with the separation of fiber and matrix at their interface. The same stress-strain behavior is observed experimentally. Results of edge replica experiments and mechanical unloading from stress levels above the knee are also presented as additional evidence of the association of fiber-matrix separation with the knee in the transverse tensile stress-strain curve.

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