Developing constitutive equations for polymer foams under cyclic loading.

摘要

Sandwich constructions with polymer foam cores have widespread applications by offering high bending stiffness and strength per unit weight. They can also dissipate energy when subjected to shock and impact loadings. The current foam models are based on metallic foams, which can describe polymer foam behavior under monotonic loading but not under cyclic or vibration loadings. Cyclic compression and pure shear tests were done on Divinycell PVC H100 foam to produce hysteresis data in compression and shear in the in-plane and out-of-plane directions of the foam with strain rates ranging from 0.0005 1/s to 5 1/s. The compressive strain amplitudes were limited to less than 10%, while the engineering shear strain amplitudes were less than 20%.;Two one-dimensional constitutive models were developed from the test data. The first constitutive model consisted of an equilibrium spring in parallel with a Maxwell element and in series a Prandtl element. Material properties were introduced for permanent crushing of cells (plastic deformation) and progressive damage of cells (Mullins effect). This constitutive model was able to capture yielding, viscoelastic and viscoplastic response, as well as hysteresis of the foam, but it failed to describe the strain-rate dependency that was found in the experiments. The second constitutive model consisted of an equilibrium spring only in parallel with a Maxwell element. This model was based on the concept of damage initiation and evolution of the foam. The damaged material properties were found to depend on the magnitude and history of the deformation. Good agreement with out-of-plane compression test results was reported with the second constitutive model.