Compaction of a double-layered metal foam block impacting a rigid wall

• The phenomena that develop at the interface between the foam layers is revealed.
• The plastic strains being velocity dependent are obtained as a part of the solution.
• Compaction of the layers due to increasing and decreasing velocity is distinguished.
• A secondary foam compaction is shown to increase the maximum interface stress.

The propagation of compaction waves in layered metal foam materials subjected to impact loading is analysed in order to examine the mechanism of compaction and reveal the phenomena that develop at the interface between the foam layers. The analysis is focused on double-layered configurations in which the individual materials exhibit strain hardening in the quasi-static regime of loading.Complex patterns of compaction due to impact are revealed depending on the foam quasi-static stress–strain characteristics, sequence of layers and impact velocity. The compaction of the individual foam layers under an increasing and decreasing velocity is distinguished. It is established that either a strong discontinuity wave or a simple compression wave can start propagating from the layers interface inside the distal layer depending on the material properties. It is shown that a secondary compaction of the proximal foam layer is possible to occur due to the propagation of the reflected wave from the layers interface when a particular layer sequence is arranged. This can lead to a significant stress increase at the interface.The present analysis is based on uniaxial models of compaction in which the compacted strains are not predefined but are obtained as a part of the solution being functions of the velocity variation. The proposed analytical models are verified by numerical simulations considering aluminium based foam Cymat with densities 253 and 570 kg/m3 and Alporas with density 245 kg/m3. The influence of the elastic material properties is briefly discussed.