Abstract
This paper intends to investigate the time-dependent mechanical characteristics of seat foams and to suggest a process for predicting the viscoelastic deformation of seat foam in response to long-term driving. To characterize the seat materials, uniaxial compression and tension tests were carried out for the seat foam and stress relaxation tests were performed for evaluating the viscoelastic behavior of the seat foam. A unit solid element model was used to verify the reliability of the material model with respect to the compression behavior of the seat foam. It is not straightforward to evaluate the time-dependent compression of foams using the explicit solver because the viscoelastic material model is limited. To use the explicit solver, the material model must be modified. Normalized stress relaxation moduli were added to the stress–strain curves obtained under static conditions to achieve a time-dependent set of stress–strain relations that were compatible with the implicit solver. To describe the viscoelastic characteristics, the time-dependent stiffness data were used, and the response to compressive loading was simulated over 2 hours. This analysis was carried out using eight sets of time-dependent stress-strain relations. An experimental measurement was also conducted with the same conditions to characterize the variation of the load with time. There was good agreement between the analysis results and experimental data.
KEYWORDS – seat foam, comfort, long-term driving, viscoelasticity, stress relaxation