Real time characteristics of tractor seat cushion materials

In tractor seat design, the properties of most cushion materials specified by the manufacturers are based upon static test method. The in-service mode of a tractor, however, is dynamic rather than static. Therefore, the overlooked real time dynamic properties of seat cushion materials are of greater importance for tractor operator comfort than static properties such as density and force-deflection. In this study, an indentation force-deflection indentor was used to load seat cushion materials under a dynamic mode, comparable to actual loading conditions in tractor operation. This test provided several real time properties such as mean dynamic loaded and unloaded height, dynamic modulus, dynamic hysteresis, and support factor in a relatively short period of time (8 h). It was observed that dynamic loaded height,, unloaded height and dynamic hysteresis decreased with flex time while dynamic modulus and support factor increased with flex time for most of the seat cushion materials. The synthetic rubber foam cushion materials D (thickness of 54 mm, density of 68.70 kg m(-3)) and 1.9D (thickness of 101 mm, density of 69.72 kg m(-3)) may be recommended for tractor seats on the basis of real time properties. The measurement of real time properties of seat cushion materials will help to reduce the need for extensive and rather costly field evaluation of tractor seats. (C) 2001 Silsoe Research Institute.