Measurement of the responses of polyurethane and CONFOR™ foams and the development of a system identification technique to estimate polyurethane foam parameters from experimental impulse responses

Vaidyanadan Sundaram, Purdue University

Abstract

Flexible polyurethane foam is the main cushioning element used in car seats. Optimization of an occupied seat's static and dynamic behavior requires models of foam that are accurate over a wide range of excitation and pre-compression conditions. Experiments were conducted to measure the response of foam over a wide range of excitation which include slowly varying uniaxial compression tests on a 3 inch cube foam sample, base excitation and impulse excitation test on a foam-mass system. The foam used was the same in all of the experiments, thus obtaining all the responses on the same foam sample which helps eliminate the sample to sample variation. Similar efforts were taken to conduct impulse and base excitation tests on CONFOR™ foam to help in future modeling efforts of CONFOR™ foam. All the experimental protocols and data pre-processing protocols along with results are presented. Previous researcher developed a linear model for a single-degree of freedom foam-mass system subjected to an impulsive excitation. Free response data from impulse tests on a foam-mass system with different masses was used to identify model parameters at various pre-compression levels (settling points). The free response of the system was modeled as a Prony series (sum of exponentials) whose parameters can be related to the parameters in the foam-mass system model. Models identified from tests at one settling point performed poorly when used to predict the response at other settling points. In this research, a method is described to estimate the parameters of a global model of the foam behavior from data gathered in a series of impulse tests at different settling points. The global model structure includes a nonlinear elastic term and a hereditary viscoelastic term. The model can be used to predict the settling point for each mass used and, by expanding the model about that settling point, local linear models of the response to impulsive excitation can be derived. From this analysis the relationship between the local linear model parameters and the global model parameters was defined. A series of experiments were conducted using different sized masses on the foam block. For each mass, the settling point was measured and the free response after an impulsive excitation was modeled as a Prony series whose parameters can be related to the parameters in the local linear dynamic model. By using the relationship between the local and global model parameters and estimates of the local models' parameters, the parameters of the global model were estimated. The estimation method was first applied to simulation data and then used to identify models of the uniaxial dynamic behavior of polyurethane foam blocks.

Degree

M.S.M.E.

Advisors

Bajaj, Purdue University.

Subject Area

Mechanics|Mechanical engineering|Materials science

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