Dynamic Enhancement and Multi-axial Behavior of Honeycombs under Combined Shear- Compression Doctoral Committee

III Abstract: This study aims at the energy absorption problems in the crash of high speed vehicles, bird impact and crashworthiness design of aircraft, and the dynamic enhancement and multi-axial behavior of honeycombs under combined shearcompression are investigated. The study consists mainly of two parts. The first part is related to the dynamic strength enhancement of honeycombs under uniaxial compression. We firstly study this particular phenomenon of thin-walled structure by establishing three micro-size FE models in order to validate the adaptability of an inertia effect model in explaining the dynamic enhancement of micro-size thin-walled structures. Further more, the dynamic enhancement of a series of honeycombs with different cell-size, cell-wall thickness and base material is studied experimentally and the influence of these geometric parameters and the base material on honeycomb strength as well as the dynamic enhancement rate is investigated. The second part of this study concerns the biaxial behavior of honeycombs under combined shear-compression. We firstly present a combined dynamic shearcompression loading device basing on a large-diameter Nylon Split Hopkinson Pressure Bar system (SHPB). The measuring and data processing methods are studied and validated by the full-size FEM simulation on the whole loading process. Then, a series of experiments on an aluminium honeycomb is performed with loading angles ranging from 0 (corresponding to the pure compression) to 60 both dynamically and quasi-statically. It shows a strong effect of the additional shear loading to honeycomb overall strength, where, both the initial peak and the crush strength decrease with increasing loading angles. A notable strength enhancement under impact loading is observed for all the honeycomb specimens. Images captured during quasi-static and impact tests permit for the determination of the two co-existing deforming patterns under combined shear-compression and also for indicating the influence of loading rate on the occurrence of these two patterns. Finally, the combined shear-compression tests on honeycombs are reproduced by a numerical virtual model and the separated normal and shear behaviors of honeycombs under combined shear-compression are obtained. It is found that the normal strength of honeycomb decreases with increasing shear loading and the shear strength behave in an opposite way. A significant dynamic strength enhancement found in experiments was validated again in the numerical work. A crushing envelope in normal strength vs. shear strength plane was obtained te l-0 06 75 75 0, v er si on 1 1 M ar 2 01 2