Effect of a fullerene C$_{60}$ addition on the strength properties of nanocrystalline copper and aluminum under shock-wave loading

The Hugoniot elastic limit and the spall strength of aluminum and copper samples pressed from a mixture of a metallic powder and 2–5 wt% C$_{60}$ fullerene powder are measured under a shock loading pressure up to 6 GPa and a strain rate of $\sim$ 10$^5$ s$^{-1}$ by recording and analyzing full wave profiles using a VISAR laser interferometer. It is shown that a 5% C$_{60}$ fullerene addition to an initial aluminum sample leads to an increase in its Hugoniot elastic limit by an order of magnitude. Mixture copper samples with 2% fullerene also exhibit a multiple increase in the elastic limit as compared to commercial-grade copper. The elastic limits calculated from the wave profiles are 0.82–1.56 GPa for aluminum samples and 1.35–3.46 GPa for copper samples depending on the sample porosity. The spall strength of both aluminum and copper samples with fullerene additions decreases approximately threefold because of the effect of high-hardness fullerene particles, which serve as tensile stress concentrators in a material under dynamic fracture.