Thermo-viscoplastic residual stresses in metal matrix composites

A three-dimensional thermo-viscoplastic ideal method is presented to determine the interfacial and cellular stresses which arise during and from manufacturing of an ideal periodic continuous unidirectional graphite/aluminum metal matrix composite (MMC) lamina. The particular manufacturing process examined is a liquid-infiltrated cast MMC with temperature excursions from the matrix melting temperature of 933 K to room temperature. The final stress state of the aluminum matrix is found to be in the vicinity of its room temperature yield strength and essentially independent of fiber volume fraction. The interface has compressive normal tractions with an insignificant shear traction component present for fiber volume fractions less than 0·70, while for higher volume fractions, approximately one-half the interface experiences tensile normal tractions. Increased fiber volume fraction lowers fiber axial stresses and decreases the uniformity of the interfacial tractions. The magnitude of the residual stress state can be reduced from the value obtained from a constant cooling rate history by using an alternative cooling profile which has a rapid initial cooling rate of 0·75 K/s until 400 K, and a subsequent slower cooling rate of 0·2 K/min.