MODELING OF THE NONLINEAR MATERIAL BEHAVIOR OF CELLULAR SANDWICH FOAM CORE

The aim of this study is to develop a simple and reliable engineering method of modelling the non-linear behaviour of rigid cellular sandwich cores. It is assumed that shear dominates the stress state in a core and, hence, the approach is only valid when this condition is satisfied. On the basis of shear domination, the usual anisotropy associated with cellular solids can be neglected in favour of a simpler isotropic consideration. This allows the use of well-developed finite element codes for isotropic materials which account for plastic behaviour. It is shown how experimentally obtained shear properties can be converted analytically to a format suitable as input for such finite element programs, and a sandwich beam subjected to four-point bending is modelled numerically with material input according to the suggested method. The results are compared with those from an experiment in which substantial core yielding took place, and the behaviour is found to be predicted quite accurately. A numerical analysis of the ASTM C-273 shear test is used to show the validity of this test method, and thereby the data on which the suggested method of modelling must rely, well into the plastic response.