Experimental observations of the double shock deformation mode in density graded honeycombs

Abstract

Aluminum honeycomb samples with density gradients were fabricated and impact tests were conducted in order to possibly observe the double shock deformation mode proposed previously. Two different arrangements were employed for impact tests. In scenario 1, a graded honeycomb sample together with a backup mass block impinged onto an elastic Hopkinson bar, at a given velocity (Taylor type impact test). In scenario 2, a stationary sample supported at the back by a Hopkinson bar was impacted upon by a block at a velocity (direct impact test). Deformations of the graded honeycombs and force histories were recorded in both the loading scenarios. The deformation mode was related to the impact velocity. Observation of the deformation process, in particular, the distributions of the local engineering strains, confirms the double shock mode. Forward and backward densification fronts were observed. Furthermore, analytical modeling for Taylor type impact is implemented based on a one – dimensional shock theory. Compared with the experiments and numerical simulations, the analytical model can predict the stresses at both the proximal and distal ends. The effect of gradient is discussed in terms of the stress at impact section, energy absorption and transmitted stress of the graded honeycombs.