Three-phase syntactic foams: structure-property relationships

Abstract

This study addresses a unique problem that occurs in composite materials containing hollow reinforcements, that is the density-filler content relationship. Unlike a traditional solid reinforcement, a hollow reinforcement can be manufactured with a variety of densities. Subsequently, when fabricating composite materials with a particular density requirement, a large variation in volume percent of that reinforcing phase can occur. Hollow reinforcements under consideration are carbon microballoons (CMBs) of various densities determined by both tap density and pycnometry. Our approach is to study several different densities and volume percents of microballoons while maintaining a constant volume percent (8.5%) of the polymer binder phase. The resulting syntactic foams are three-phase materials consisting of binder, microballoon (MB), and interstitial void phases. The volume of the MB and binder phase is measured by helium pycnometry. The complementary volume of the interstitial void phase will depend on the volume of microballoons in the billet. Mechanical characterization is done by compression and flexure testing and results are discussed to highlight structure-property relationships. Results show that, in addition to bulk density of the foam, the packing arrangement of the CMBs is an important factor in the mechanical behavior of the foam and is shown to be an important design criterion.