| The damping properties of metal matrix composites is of interest in structural applications, such as space structures, where it is felt that the material damping could contribute significantly to minimizing unwanted vibrations. This investigation focuses on the experimental and analytical aspects of damping mechanisms in particulate metal matrix composites. Experimental testing was carried out at the Product Engineering Center, A. O. Smith Automotive Products Co., Milwaukee, Wisconsin. It used an instrumented hammer, an accelerometer, and a Zonic 6088 Fast Fourier Transform frequency analyzer to determine the damping ratios of a variety of test samples being subjected to free vibration. The damping ratios were obtained by using the half power bandwidth technique.; Analysis was developed to compare a theoretical prediction of the damping ratio with the experimental data. In general, the damping ratio could be expressed as the summation of a strain-independent term and a strain-dependent term (37). The strain-dependent term was related to interfacial slip-relative movement occurring between the particles and the matrix which led to energy dissipation at the interface. This effect was predominant when the bond between the particles and the matrix was characterized by voids, or the strain the material was subjected to was relatively high. If the bond between particles and matrix is absent of voids, or the strain the material is subjected to is relatively low, than interfacial slip does not occur and the damping ratio is normally equal to that of the matrix. This is strain-independent damping.; The materials with bonds absent of voids between particles and matrix are SiC/6061Al from DWA, 10% Al{dollar}sb2{dollar}O{dollar}sb3{dollar}/6061Al, and 20% Al{dollar}sb2{dollar}O{dollar}sb3{dollar}/2014Al from Dural. The damping ratios of these materials are equal to the damping ratios of the respective aluminum matrices. The 10% Flyash/A356Al composite from UWM has some voids at the interface between particle and matrix but its damping ratio is slightly greater than that of aluminum. The materials that have voids at the interfaces between particles and matrix are SiC/6061Al from DWA, 10% Al{dollar}sb2{dollar}O{dollar}sb3{dollar}/6061Al and 20% Al{dollar}sb2{dollar}O{dollar}sb3{dollar}/2014Al from Dural, and Flyash from UWM. The damping ratios of these materials are equal to the damping ratios of the respective aluminum matrices. The materials with a relatively weak bond between particles and matrix are cast particulate composites from Fiber Materials Inc.--SiC/AZ91, B{dollar}sb4{dollar}C/AZ91, and B{dollar}sb4{dollar}C/2014Al. The damping ratios of SiC/AZ91, B{dollar}sb4{dollar}C/AZ91, and B{dollar}sb4{dollar}C/2014Al are about 2, 5, and 10 times that of their matrices. Theoretical computations based on interfacial slip produce errors of 25%, 17%, and {dollar}-{dollar}29%. The correlation could be improved if the coefficients of friction between the particles and matrix at the interfaces as well as the volumetric fractions were known more accurately. |
