Quasi-static crush behavior of aluminum honeycomb specimens under compression dominant combined loads

The influence of shear stress on the quasi-static crush behavior of aluminum honeycomb specimens under compression dominant combined loads is investigated by experiments. A test fixture was designed such that dominant compressive and shear loads with respect to the strongest material symmetry direction can be controlled and applied independently. Honeycomb specimens were also designed such that the secondary non-uniform stresses due to the stress-free boundary can be minimized. The experimental results indicate that the normal crush strengths under combined compressive and shear loads are lower than that under pure compressive loads. A phenomenological yield criterion for specimens with different in-plane orientation angles is proposed based on the experimental normal crush and shear strengths under combined loads. The experimental results suggest non-normality plastic flow based on the yield criterion. The non-normality flow behavior becomes more pronounced as the in-plane orientation angle increases. The experimental results also indicate that the energy absorption rate depends upon the ratio of the shear stress to the compressive stress and the in-plane orientation angle. In addition, specimens crushed under combined loads show inclined stacking patterns of folds due to the asymmetric location of horizontal plastic hinge lines and the rupture of aluminum cell walls along the adhesive lines. These experimental observations are useful to develop microscopic plasticity models of aluminum honeycombs under compression dominant combined loads.