Master of Science (MS)
This thesis deals with the characterization of hybrid syntactic foams under high strain rates (HSR) ranging from 450/s to 1000/s. The foams studied are comprised of epoxy resin matrix filled with 63% volume fraction glass microspheres and 2% volume fraction of ground rubber fragments. The focus of this study is to compare the strength, ultimate strain, and modulus of these composite materials at high strain rates and quasi-static conditions and to find out the effects of HSR on the failure mode and fracture behavior of these materials. Split Hopkinson Pressure Bar (SHPB) apparatus is used for the HSR testing. Foams of four different densities were fabricated by using four different microspheres in order to observe the density effect on the HSR properties. The microspheres have the same average outer diameter of 40 μm, but different wall thickness leading to a difference in their density. Rubber particles with an average size of 40 μm were also added in these four samples to study the effect of the rubber on their properties. Fracture surfaces were observed under a scanning electron microscope to understand the fracture behavior of these materials and the influence of the rubber particles. The peak stress was found to increase as the strain rate increased for all types of foam. For the hybrid foams fabricated with the lightest density (S22 and S32 types) microspheres with the 40 μm rubber particles the modulus values had an nearly constant value as the strain rate increased. For these foams, the fracture surfaces showed damage to the microspheres. The heavier density foams that used the S38 and K46 microspheres with the 40 μm rubber particles had an increasing modulus as the strain rate increased. The fracture surfaces showed failure of the epoxy matrix as the principal failure mode. A further two samples were fabricated that utilized rubber particles that were 75 μm in diameter. Compared to the smaller rubber particles in the same density of foam, the testing showed that the larger rubber particles resulted in a 20% increase in peak stress and the modulus increased.
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Wehmer, Paul, "High strain rate characteristics of rubber modified syntactic foams" (2008). LSU Master's Theses. 3587.