Analyses of impact energy-absorbing performance of open- and closed-cell Al foams using modified split Hopkinson pressure bar

Abstract

Al foams have been developed to meet increasing demands for effective reduction of impacts in military, automotive, civil-engineering, and aerospace applications. However, evaluating their energy-absorbing performance is very difficult, as most of the impacted energy is quickly dissipated as interior pores are rapidly closed. In this study, a split Hopkinson pressure bar (SHPB) was modified by utilizing the incident wave alone, using a deceleration-measuring module placed between the striker and incident bars to reliably evaluate the energy-absorbing performance of open- and closed-cell Al foams with different densities and porosities. The impact momentum (Ibar), which was regarded as the overall energy of the incident wave produced by the impact of the striker bar, and the maximum impact acceleration (amax), which indicated the largest change of impact velocity, were used as main evaluation parameters. The ratio of the reduced amount of amax in comparison with the amax of the none-specimen case, i.e., amax reduction ratio, was lowest in the open-cell low-density specimens and increased as the specimen thickness or density increased, i.e., in the order of the open-cell high-density, closed-cell low-density, and closed-cell high-density specimens. Thus, the thicker higher-density foam specimens worked more effectively for the better energy-absorbing performance. The present modified SHPB is outstanding for the energy-buffering concepts and mechanism-focused interpretations of the amax and Ibar data, since the quantitative energy-absorption analyses have hardly been conducted because of the energetic and mechanical complexities. It also provides an excellent idea to improve or develop various Al foams having high amax reduction ratios.