Linking of Continuum and Microstructure Models of Foam to Aid in the Design of Automotive Seating

Polyurethane foam is often a major constituent of automotive seating, and exhibits highly nonlinear behavior under normal operating conditions. Efficient design requires an understanding, as well a good model, of the foam behavior. The work presented here is an attempt to link continuum and microstructural approaches to modeling foamed materials and take advantage of the utility in each. The outcome will ultimately be the ability to generate a foam superelement that is sensitive to microstructural properties but does not require the computational complexity of a microstructural finite element model. This will facilitate the iterative design of seating for comfort and other dynamic considerations. To this end, an Ogden-type continuum model for compressible rubber-like solids, is fitted to the results of numerous simulated compression tests conducted on finite element models of two-dimensional foam. The structure of the finite element model of foam is constructed using Voronoi tessellations that provide the ability to incorporate realistic irregularity into the foam microstructure. The continuum model parameters are studied as a function of the microstructure variables relative density, cell regularity, sample size relative to the characteristic length of the microstructure, and the sample aspect ratio.