Matrix strengthening mechanisms of an iron fiber-copper matrix composite as a function of fiber size and spacing

Copper matrix-iron fiber composites of fiber diameters from 10 to 5 × 10⁻³ mils and volume fractions from 0.03 to 0.97 were fabricated in order to study the dependence of mechanical properties on these variables. Composite elastic moduli agreed well with the predictions of the rule of mixtures. However, matrix and composite yielding and plastic flow were quite dependent on fiber diameter and spacing, exhibiting positive deviations from the simple rule of mixtures by factors of more than five in some cases. Yielding behavior may be explained by a combination of dislocation extrusion and pileup models for low volume fractions of fiber. Triaxiality generated by the difference in Poisson coefficients of the phases inhibits matrix yielding in higher volume fraction composites, allowing matrix flow only when the fibers also yield. Formerly with the Department of Metallurgy and Materials Science, M.I.T., Cambridge, Mass. Formerly with the Department of Metallurgy and Materials Science, M.I.T.