Effects of macroscopic bulk defects on the damping behaviors of materials

A large number of macroscopic pores or graphite particulates were introduce d into commercially pure Al and ZA27 alloy by infiltration process to compa ratively study the influence of macroscopic defects on the damping behavior s of the materials. The mean diameter of the bulk defects is (1.0 +/- 0.5) mm, and the volume fractions of pores and graphite particulates are in the range of 50%-75% and 19%-94%, separately. It is shown that addition of a nu mber of pores or graphite particulates can significantly improve the dampin g of commercially pure Al, due to the comprehensive effects of the macrosco pic and microscopic defects. However, the pores have little effect on the d amping capacity of high damping ZA27 alloy, and graphite particulates make the high temperature internal friction peak decrease. It is considered that graphite particulates may repress the intrinsic damping mechanism of ZA27 alloy.