CHARACTERIZATION OF MECHANICAL STRESSES IN METAL-MATRIX COMPOSITES BYINTERNAL-FRICTION

In MMC the matrix is exposed to plastic deformation and damage accumul ation in the region close to the reinforcements, following mechanical or thermal stress. In this connection, Al-4%Cu based MMC reinforced wi th 10, 20 and 30% Al2O3 fibers were studied by internal friction (IF) measurements. When mechanical stresses are relaxed by damage accumulat ion at interfaces, the IF measurements as a function of the vibration amplitude exhibit a peak P which has been connected with solid frictio n at metal-fiber interfaces and interface loosening. When, on the othe r hand, mechanical stresses at interfaces are relaxed by plastic defor mation of the metal matrix, a saturation is observed in the vibration amplitude reached after three vibration cycles. On this basis, the IF measurements allowed us to characterize the relaxation of mechanical s tresses at matrix-fiber interfaces in different composites. Copyright (C) 1996 Acta Metallurgica Inc.