MEASUREMENT OF INTERFACIAL SHEAR PROPERTIES OF COMPOSITES OF TI-1100 ALLOY REINFORCED WITH SCS-6 SIC MONOFILAMENT FIBER

The commonly used thin-slice fiber push-out or pull-out tests to measu re interface properties of fiber-reinforced metal-matrix composites ca n introduce biaxial bending of metallic matrix around the fiber and ge nerate 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 i n which a model, single-ply multi-fiber composite specimen is tested i n a state of nearly pure shear. The chief advantages of this technique are that specimen preparation and test methodology are simplified, an d the influence of non-shear stresses, such as those associated with t he fiber push-out or pull-out test, are minimized. Composite shear str ength has been measured as a function of fiber packing density. A meth od of interpreting the shear strength data, which includes contributio ns from fiber-matrix debonding strength as well as shear fracture stre ngth of the matrix, has been developed. The method permits measurement of the interfacial shear strength and an assessment of matrix residua l stress generated due to CTE difference between the matrix and the fi ber. 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 inte rfacial strength in Ti-1100/SiC fiber composites. Microstructures and interface chemistries of as-fabricated composites and sheared composit e surfaces are also presented.