Measurement of interfacial shear properties of composites of Ti-1100 alloy reinforced with SCS-6 SiC monofilament fiber

Abstract

The commonly used thin-slice fiber push-out or pull-out tests to measure interface properties of fiber-reinforced metal-matrix composites can introduce biaxial bending of metallic matrix around the fiber and generate complex interfacial stress states. These factors complicate the interpretation of results from these tests. Also, the results from a single fiber push-out (or pull-out) test might not directly relate to the shear properties associated with an assemblage of fibers as in an actual composite body. In this paper, a technique has been presented in which a model, single-ply multi-fiber composite specimen is tested in a state of nearly pure shear. The chief advantages of this technique are that specimen preparation and test methodology are simplified, and the influence of non-shear stresses, such as those associated with the fiber push-out or pull-out test, are minimized. Composite shear strength has been measured as a function of fiber packing density. A method of interpreting the shear strength data, which includes contributions from fiber-matrix debonding strength as well as shear fracture strength of the matrix, has been developed. The method permits measurement of the interfacial shear strength and an assessment of matrix residual stress generated due to CTE difference between the matrix and the fiber. The method has been used to study the effect of surface coatings on SiC fiber, e.g. C-rich coating (SCS-6) and TiN coating, on the interfacial strength in Ti-1100/SiC fiber composites. Microstructures and interface chemistries of as-fabricated composites and sheared composite surfaces are also presented.