Measurement and modeling of the mechanical properties of flexible polyurethane foam

Richard D. Widdle, Purdue University

Abstract

Flexible polyurethane foam is used in a variety of engineering applications, including automotive seating. It exhibits nonlinear and viscoelastic response to mechanical loading. Accurate models are needed for effective and efficient design of seating systems utilizing this material. The overall objective of the present investigation was to measure and model the mechanical behavior of open-cell, flexible polyurethane seating foam. Attention was restricted to planar deformation of the material. The mechanical response to uniaxial compression, as well as compression and shear, was measured using foam samples of two relative densities. Additionally, the material's Poisson's ratio was investigated for the case of uniaxial compression. Modeling was approached from two points of view. First, the microstructural modeling approach consisted of representing the microscopic features of the material directly. Irregularity, that exists in a real foam, was modeled by using Voronoi tessellations. While, two-dimensional (2D) and three-dimensional (3D) microstructural models were constructed, parameter studied were restricted to the 2D models for computational expediency. Uniaxial and combined compression and shear tests were simulated on numerous realizations of these models for a variety microstructural model parameters. The simulations were preformed by using the finite element method. The second approach is referred to here as the continuum modeling approach because the extent of the material was assumed to be much larger than the characteristic length of the microstructure. Nonlinear viscoelastic continuum-based models were developed for the mechanical response of the foam material. An additive decomposition of the stress response into a nonlinear elastic component and a linear viscoelastic component was assumed. The nonlinear elastic model component was based on a hyperelastic model commonly used in the study of rubber elasticity. The linear viscoelastic component was modeled with a hereditary-type integral that utilizes a sum of decaying exponential terms for the viscoelastic kernel. System identification techniques were developed to estimate the parameters of the continuum models from experimental data, as well as the response data from simulated tests on the microstructural finite element models. The relationship between the microstructural and continuum model parameters was also investigated.

Degree

Ph.D.

Advisors

Davies, Purdue University.

Subject Area

Mechanical engineering|Materials science|Plastics

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