TRANSIENT INTERNAL DAMPING IN METAL-MATRIX COMPOSITES - EXPERIMENT AND THEORY

In this presentation, first, 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 sho wn that a broad low temperature peak appears in the low frequency inte rnal damping (ID) spectra of aluminium based microheterogeneous materi als. The role of the various experimental and material parameters is p resented. Concerning material parameters, in addition to the influence s of the matrix microyield stress and volume fraction of reinforcing p articles, the role of particle - matrix Interfacial region is carefull y investigated. From the overall experimental observations it is prove d that the transient ID phenomena are linked with emission and movemen t of dislocations around particles, which results from the micromechan ical interaction between particle and matrix. Moreover, assuming a per fect particle-matrix interface, a dislocation model has been developed in order to account quantitatively for the observed phenomena. The pr edictions of the model agree fairly well with the experimental behavio ur 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 id entify the mechanism liable for the differences between the correspond ing ID spectra.