Experiments and full-scale numerical simulations of in-plane crushing of a honeycomb

The in-plane mechanical behavior of honeycombs has been widely used as a two-dimensional model of the behavior of more complicated space filling foams. This paper deals with the mechanisms governing in-plane crushing of hexagonal aluminum honeycombs. Finite size honeycomb specimens are crushed quasi-statically between parallel rigid surfaces. The force-displacement response is initially stiff and elastic but this is terminated by a limit load instability. Localized crushing involving narrow zones of cells is initiated and subsequently crushing spreads through the material while the load remains relatively constant. When the whole specimen is crushed the response stiffens again. It has been found that although the crushing patterns that develop during the load plateau vary from specimen to specimen (influenced by geometric imperfections and by specimen size) the underlying cell collapse mechanism is common to all specimens. As a result, the level of the stress plateau and its extent in strain are quite repeatable. The crushing process is simulated numerically by full-scale FE models in which the geometric characteristics of the actual cells are used. The manufacturing of the honeycomb involves cold expansion of specially bonded aluminum sheets. This is simulated numerically in order to reproduce the material changes and residual stresses introduced to the aluminum by the process. The expanded honeycomb is then crushed as in the experiments. It is demonstrated that once the key geometric, material and processing parameters are incorporated in the models, the simulations reproduce the experimental results both qualitatively as well as quantitatively. (C) 1998 Acta Metallurgica Inc.