1. Introduction

Mechanical properties of polyurethane foams compressed during fast and dynamic states are among others affected by a friction of the cellular structure and the air contained in the cells [1–3]. However, this does not significantly contribute to a compressive force in certain range of the deformation as reported in Ref. [4]. On behavior under compression, loading a significant influence has mechanical and physical properties of the PU foam such as a geometry, thickness, or density, which is explained by [5]. A decrease of the thickness of the comfort stuff from polyurethane foam brings desired weight reduction, but it reduces the total damping, and on the contrary, the total stiffness increases. Therefore, the trend in automotive industry has been a development of low density polyurethane foams with lower bulk density having better

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

mechanical properties under compression than commonly used PU foams [2]. Another solution that can change mechanical properties is a vertical layering of polyurethane foams having different physical and mechanical properties. But it does not bring an expected improvement of characteristics corresponding with a composite behavior [6, 7], which may be due to the fact that only the layering of polyurethane foams does not bring the desired synergistic effect as stated by Ref. [8]. Also, a significant improvement in energy savings and vibroisolation characteristics or other parameters such as a permeability of PU foam is not achieved. The improvements are reflected only in reduced values of contact pressures from the load body [9]. The mechanical behavior of polyurethane foams can be considered substantially non-linear, with a large viscoelastic deformation, relaxation, and recovery of the structure.
