Numerical prediction of the viscoelastic deformation of seat foam in response to long-term driving

Abstract

The aim of this paper is to carry out a quantitative evaluation of the time-dependent mechanical characteristics of seat foam and to suggest a process for predicting the viscoelastic deformation of the seat assembly in response to long-term driving. Several tests were conducted to obtain the mechanical properties of the seat components, and the test data were applied in the construction of the material models of the foam pad, the slab foam and the seat cover. An explicit solver (PAM-COMFORT® from ESI) was used to analyse and construct the seat assembly model, and we assumed that the time-dependent behaviour of the seat foam is based on degradation of the material. To describe the behaviour, we used time-dependent stress–strain relationships to account for the viscoelastic characteristics of the seat foam to enable the PAM-COMFORT solver to be used. On multiplying the normalized relaxation modulus by the stress–strain relation, the time-dependent stress–strain relationships can be obtained. In this approach, the material modelling is not a direct method to describe the viscoelasticity using a built-in material model in the commercial program. In order to verify the process, an indenter was used to apply a compressive load to the seat, and the time dependences of the applied load and the deformation were measured experimentally and compared with the results of the numerical analysis. There was good agreement between the experimental results and the numerical analysis results.