Studies are being made of fiber-reinforced metals and alloys to evaluate their mechanical properties The deformation characteristics of v rious composites were studied to determine 1 the strengthening mechanism of the composite and 2 why the yield strength is dependent upon the type of fiber. micro-yield measurements were made on composite specimens of Ag-10 mild steel and Ag-30 mild steel fibers 0.0025 to 0.003 in. in diameter, and on Ag with 30 fibers of mild steel, Mo, and heat-treated hardened type 410 stainless steel. The surface of a Cu-30 Mo fiber composite was polished and examine metallographically as a function of strain. Failed sections of Cu-10 and -40 Mo fiber composites were examined. Three important features in the deformation behavior of fiberreinforced metals are 1 for a given type of fiber, the rate of work hardening is highly dependent on fiber density at small plastic trains, and relatively independent of fiber density at high strains 2 for the initial 2 elongation, deformation is restricted to the softer matrix and 3 for a given matrix, fiber size, and fiber density, the yield strength at small strains is nearly indepe dent of the type of fiber, but becomes significantly dependent at higher strain .