In-plane uniaxial and biaxial crushing of a polycarbonate honeycomb

The uniaxial and biaxial in-plane crushing of honeycomb is studied through a combination of experiments and analyses. The honeycomb has circular thin-walled polycarbonate cells in a hexagonal arrangement. Under displacement controlled uniaxial compression, the force-displacement response is characterized by three regimes of behavior. In the initial rising part of the response, the deformation is essentially uniform throughout the specimen. Following the load maximum, the deformation localizes in a narrow zone of cells. Collapse then propagates through the specimen while the load remains relatively constant until all the cells have collapsed at which point the load rises sharply. As a result of the rate dependence of the material, the initiation and propagation stresses increase as the rate of crushing of the honeycomb is increased.;This crushing process was simulated numerically through the finite element method. The developed models properly address the nonlinearities due to geometry and contact. An elastic-power law viscoplastic constitutive rule is used to model the behavior of the polycarbonate. Results from analyses involving a characteristic cell and from full scale simulations of the experiments are in excellent agreement with the experimental results.;Biaxial crushing was performed in a custom biaxial test facility. This facility is capable of crushing specimens in two orthogonal directions simultaneously to volume reductions of nearly 95%. Approximately square specimens were crushed between rigid platens at different biaxiality ratios by varying the two speeds of crushing. The onset of collapse involves localized instabilities as in the uniaxial crushing. However, the extent of the localized deformation varies with the biaxiality ratio. The prevalent mechanisms of collapse as well as the energy absorption capacity of the material also depend on this ratio. The highest energy is required when the specimens are crushed at the same rate in the two directions.;Finite element simulations of the biaxial crushing were also performed. The models in these calculations were smaller than the specimens used in the experiments. As a result, the responses differ slightly in the initial stages of crushing, but for larger strains, the predictions agree well with the measurements. The calculated amounts of energy absorbed are in excellent agreement with the experiments. In addition, many of the modes of cell collapse seen in the experiment are reproduced in the simulations.