High Strain Compressive Response

When a closed cell foam is uniaxially compressed, it can be assumed that the compressive stress is a sum of the stresses taken by the polymer structure and that taken by the cell gas. For a foam with zero lateral expansion when uniaxially compressed, and isothermal gas compression, the latter contribution (Tg is given by (295)  

Mills and Zhu (a. 15) used a Kelvin foam model, in which face tensions restrain the bending of cell edges 

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Micromechanics theories for closed cell foams are less well advanced for than those for open cell foams. The elastic moduli of the closed-cell Kelvin foam were obtained by Finite Element Analysis (FEA) by Kraynik and co-workers (a. 14), and the high strain compressive response predicted by Mills and Zhu (a. 15). The Young s moduli predicted by the Kraynik model, which assumes the cell faces remain flat, lie above the experimental data (Figure 7), while those predicted by the Mills and Zhu model, which assumes that inplane compressive stresses will buckle faces, lie beneath the data. The experimental data is closer to the Mills and Zhu model at low densities, but closer to the Kraynik theory at high foam densities. 

In the plastic response of semi-crystalline polymers the starting material has an initial spherulitic morphology and, in the process of simple extensional flow, either in tension or in plane-strain compression, ends up with a highly perfect... 

The Poisson s ratio can be determined by measuring the transverse strain during uniaxial tension or compression experiments. Due to the small magnitude of the transverse strain, it is difficult to accurately determine the Poisson s ratio. Instead, it is often sufficient to assume a value for the Poisson s ratio of about 0.4. Unless the fluoropolymer component is highly confined, the Poisson s ratio has only very weak influence on the predicted material response. 

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