Crushing behavior of honeycomb vs. foam under combined shear-compression loading

This paper conducts a combined compression-shear test on honeycombs and Kelvin foams to compare their yield envelopes. The honeycomb and foam specimens with a similar relative density are fabricated by using the additive manufacturing technique. The quasi-static and dynamic crushing behaviors under combined shear-compression are investigated by employing a universal testing machine and a rotatable Hopkinson bar system, respectively. Five loading angles ranging from 0 degrees to 50 degrees are considered. Results reveal that the normal strengths of both honeycomb and Kelvin foam decrease while the shear strengths increase with the loading angle increasing. Moreover, honeycombs change the deformation mode from the progressive folding mode to the global rotation mode while Kelvin foams maintain the layered folding mode as the loading angle increases. Therefore, honeycombs show the normal strength decreasing more sharply than Kelvin foams. As a result, although honeycombs possess higher normal strengths than Kelvin foams under pure compression, the difference becomes smaller with the increase of loading angle. There is a cross point on the macroscopic yield envelopes of honeycomb and Kelvin foam. At this point, honeycomb and Kelvin foam possess the same normal and shear strengths. Moreover, the dynamic yield envelopes of both honeycombs and Kelvin foams possess an almost isotropic expansion of quasi-static envelopes due to the loading rate effect. These yield envelopes provide design criteria for cellular materials to withstand any applied shear and compressive stress state.