Quasi-static crushing behavior of aluminum honeycomb materials

The quasi-static crushing behavior of aluminum honeycomb materials is thoroughly evaluated using a combined experimental, analytical, and numerical approach. Based on experimental characterization, the constitutive properties of the honeycomb cores under flat-wise compression are approximated by an elastic perfectly plastic material with inclusion of hardening after densification. Two different cell size materials are tested and compared, and the effect of strain rate on the crushing stress is studied. The experimental results show that the crushing platen stress is directly related to the relative density of core materials, and it can be associated with the strain rate, even though the effect of strain rates is not so dominant based on the conducted quasi-static tests. A simple physical model for predicting the crushing wave length and stress is proposed and compared with the experimental data and available formulas in the literature. It is observed that the crushing wave length is close to the cell size and related to the geometric dimension and strain rate. The folding mechanism is also measured by the ARAMIS system (a photogrammetry technique), and the measured von Mises strains are compared with the numerical results from LS-DYNA, demonstrating that the folding mechanism is initiated by two plastic hinge lines formed at the cell corners. Multilayer effect is also investigated, and it indicates that including the second layer slightly decreases the maximal crushing stress, but the simple superposition is still applicable for crushing multilayer honeycomb cores with different density. Partial crushing due to small size cylindrical indenter is further studied, and the experiment shows that the partial crushing process can be described by an elastic-plastic hardening material. Side impact process of honeycomb materials is also investigated, and the collapse band and its propagation process are captured. The thorough characterization of core crushing behavior conducted in this study provides better understanding of the failure process of honeycomb materials and can be further employed to study energy absorption and impact response of sandwich structures.