Compression Response and Energy Absorption of Filled Circular Cell Honeycombs.

Abstract

Manufactured circular cell honeycombs are two-dimensional cellular solids commonly used in aerostructures as sandwich panel cores. Honeycombs are also used as energy absorbers, for instance as crash barriers in the automotive industry. There has been some progress in understanding the crush mechanisms in the static regime. However, continuum level models in the failure regime are elusive because of complex localization phenomenon exhibited by these structures. Analysis is instead done using numerical methods such as the finite element method. This study examines the compression response and energy absorption of circular cell polycarbonate honeycombs at high loading rates and when filled with soft elastomers. Synergistic behavior is reported in the compression response of filled honeycombs which simultaneously enhances the peak strength and energy absorption capability. It is also seen that the filler material stabilizes the failure path.

High rate crushing along the axial direction is examined. Since low impedance of such structures preclude the use of the conventional split-Hopkinson pressure bar (SHPB), two new experimental methods are conceived by modifying the SHPB. Deformation sequence is obtained using high speed imaging. Rate dependence in the crush response is observed. Analysis is done using the finite element method in conjunction with the commercial software ABAQUS/Explicit.

Quasi-static out-of-plane crushing of honeycomb filled with polyurethane is studied. Diffused folding is the primary failure mechanism compared to localized progressive folding in the unfilled specimen. The in-plane static response of filled honeycomb is also examined with polydimethylsiloxane (PDMS) as filler. Analysis is done using Digital Image Correlation (DIC) and the finite element method. A Smeared Crack Approach is incorporated in the numerical model to account for Mode I cracking in the cell walls. A unique energy dissipation mechanism is reported. High rate axial crushing of filled honeycombs is studied using another modified split-Hopkinson pressure bar. Here, 19-cell specimens filled with polyurethane elastomer are used. The corresponding numerical study is done using visco-hyperelastic behavior of polyurethane to capture the rate dependent response of the filled honeycomb.

This dissertation provides unique insight into controlling the deformation response of honeycombs so as to maximize the energy absorption under axial crushing.