Radius ratio effect on high-strain rate properties of syntactic foam composites

The high-strain rate compressive properties of syntactic foams are characterized in this study. This study is performed using a pulse-shaped Split-Hopkinson Pressure Bar technique. Nine different types of syntactic foams are fabricated with the same matrix resin system but three different size microballoons and three different microballoon volume fractions. The microballoons have the same outer radius of 40 μm, but different internal radii leading to a difference in their densities. The volume fractions of the microballoons in the syntactic foams are maintained at 0.1, 0.3, and 0.6. Analysis is carried out on the effect of the microballoon radius ratio at each volume fraction on the high-strain rate properties. This approach is helpful in separating and categorizing the contribution of matrix and microballoons to the dynamic compressive properties of syntactic foams. The results at high-strain rates are compared to quasi-static strain rate compressive properties of the same material. The results show that there is little or no significant change in both compressive strength and modulus of syntactic foams at all radius ratios when tested at strain rates of 400–500/s compared to quasi-static rates. However, higher dynamic strength and stiffness values are obtained consistently at all radius ratios when tested at 800–1000/s compared to quasi-static values. It is observed that the radius ratio does not affect the syntactic foam properties significantly when tested at the same high-strain rate and volume fraction. Scanning electron microscopy is carried out to understand the fracture modes of the syntactic foams.