Mechanical behavior of aluminum honeycombs under multiaxial loading conditions.

Abstract

Crush behavior of aluminum honeycombs has been experimentally investigated. First, the quasi-static crush behavior of aluminum honeycomb specimens under proportional combined loads is investigated. The combined loading tests included simultaneous compressive and shear loads parallel and perpendicular to the out-of-plane axis of the honeycomb specimens, respectively. As expected, the shear loads lower the normal crush strengths. A phenomenological yield criterion for specimens with different in-plane orientation angles is proposed based on the experimental results. The experimental results suggest non-normality plastic flow based on the yield criterion. The energy absorption rate depends upon the ratio of the shear stress to the compressive stress and the in-plane orientation angle. Secondly, the quasi-static crush behavior of aluminum honeycomb specimens under non-proportional combined loads is investigated. Combined loads and pure compressive loads were applied in different sequences to induce non-proportional combined loads. The sequence of loading paths for the non-proportional combined loads does not affect the crush strengths of honeycomb specimens. Specimens crushed under non-proportional combined loads show developments of different stacking patterns of folds in different loading regions of the non-proportional combined loads. The incremental stress-strain relation for the transition loading path from one state to another state on the crush yield surface may be related to the displacement increments that correspond to the change of microscopic folding mechanisms. Finally, the quasi-static and dynamic crush behaviors of aluminum honeycomb specimens under inclined loads are investigated. The inclined loading tests included compressive loads at an angle to the out-of-plane axis of the honeycomb specimens. The results of the quasi-static crush tests indicate that the normal crush and shear strengths under inclined loads are consistent with those under the corresponding combined loads. The results of the dynamic crush tests indicate that as the impact velocity increases, the normal crush strength increases and the shear strength remains nearly the same. The trends of the normalized normal crush strengths under inclined loads for specimens with different in-plane orientation angles as functions of the impact velocity are very similar to each other.