Mechanical Models of Cellular Solids, Parameters Identification from Experimental Tests

Cellular solids are largely used in many structural applications to absorb and dissipate energy, due to their light weight and high energy absorption capability. The appropriate design of mechanical pieces made of structural foams must be done on the basis of the kind of impact, the energy involved and the maximum admissible stress. In the design development it is of highest importance the choice of the proper type of foam at the proper density level. This is based on stress-strain behaviour that can be predicted by means of test curves and models. The parameters of two cellular solids models for EPP, PUR, EPS and NORYL GTX foams have been identified by means of experimental compression tests at different densities. The Gibson model and a modified version of this model have been considered: the fitting of these models are compared also with the Rusch model and a modified version of the Rusch model. The considered models are directly derived from theoretical micro-mechanical assumptions while the parameter values are identified by means of the available experimental data. Model parameters depend on the foam density and a mathematical formulation of this dependence is identified. The formulas of the density dependence of the model parameters permits the identification of all foams made starting from the same solid material and with the same micro-structure by means of a minimum set of experimental tests. At the same time the availability of a large quantity of experimental data allows to reach a higher confidence level for the model parameters values. The identified laws that describe parameters against density, for a certain type of foam, could be used in order to assist the design of the absorber and to find the optimum density for the specific application.