Characterization of mechanical stresses in metal matrix composites by internal friction

In MMC the matrix is exposed to plastic deformation and damage accumulation in the region close to the reinforcements, following mechanical or thermal stress. In this connection, Al-4%Cu based MMC reinforced with 10, 20 and 30% Al2O3 fibers were studied by internal friction (IF) measurements. When mechanical stresses are relaxed by damage accumulation at interfaces, the IF measurements as a function of the vibration amplitude exhibit a peak P which has been connected with solid friction at metal-fiber interfaces and interface loosening. When, on the other hand, mechanical stresses at interfaces are relaxed by plastic deformation 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 stresses at matrix-fiber interfaces in different composites. Copyright (C) 1996 Acta Metallurgica Inc.