In-plane crushing of a polycarbonate honeycomb

The in-plane compressive response and crushing of a polycarbonate honeycomb with circular close-packed cells is studied through combined experimental and analytical efforts. Under displacement controlled quasi-static loading the response is characterized by a relatively sharp rise to a load maximum followed by a drop down to an extended load plateau which is then terminated by a sharp rise in load. 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. These cells collapse in a shear-type mode until contact between cell walls arrests their deformation and causes spreading of the deformation to the neighboring rows of cells where the process is repeated. This propagation of the collapsed zone occurs at a relatively constant load and continues until all the rows of cells have collapsed. 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 process of crushing has been simulated numerically using appropriately nonlinear kinematics. An elastic-powerlaw viscoplastic constitutive rule, calibrated to uniaxial experiments spanning strain rates of six decades, is used to model the behavior of the polycarbonate. In addition, the model is capable of treating contact between cell walls which result from crushing. Results from analyses involving a characteristic cell and from full scale simulations of the experiments are presented which are shown to be in excellent agreement with the experimental results.