Transient Internal Damping in Metal Matrix Composites : Experiment and Theory

In this presentation, frst, the Internal Damping (I.D.) phenomena and related theories that have been previously reported in the literature for Metal Matrix Composites (M.M.C.s) are reviewed briefly. Then, the paper is focused on the transient ID phenomena. Especially, it is shown that a broad Iow temperature peak appears in the low frequency internal damping (ID) spectra of aluminium based microheterogeneous materials. The role of the various experimental and material parameters is presented. Concerning material parameters, in addition to the influences of the matrix microyield stress and volume fraction of reinforcing particles, the role of particle matrix interfacial region is carefully investigated. From the overall experimental observations it is proved that the transient ID phenomena are linked with emission and movement of dislocations around particles, which results fiom the micromechanical interaction between particle and matrix. Moreover, assuming a perfect particle-matrix interface, a dislocation model has been developed in order to account quantitatively for the observed phenomena. The predictions of the model agree fairly well with the experimental behaviour of MMCs for which the assumption of a perfect interface is expected to be sound. Finally, the behaviour of MMCs with modified interfacial regions is discussed, using the above mentioned model, in order to identify the mechanism liable for the differences between the corresponding ID spectra.