Dynamic Property Response of Polyurethane Foam as a Function of Test Frequency 2001-01-0323
Comfort performance has developed into a central theme of vehicle seating design due to the role of the seat as the interface between the vehicle and the human. These comfort performance requirements exercise considerable influence over the specifications of the polyurethane foam that serves as a primary load-bearing material in the seat assembly. Various test protocols have been established to measure and predict comfort performance for polyurethane foam. One of the most important test methods is the vibration transmissivity test, used to characterize the response of a material to vibration of varying frequency and energy. This test methodology measures the performance of polyurethane foam alone to the performance of a fully assembled seat in a vehicle driven on a road surface. As such, there are a variety of test conditions employed to characterize transmissivity performance.
However, the results from these various tests can be quite different depending on the test conditions employed. Furthermore, most tests measure comfort properties at some standard deflection, or pressure, which is nominally designed to represent the average population that will be riding on the seat. Missing from these tests is a recognition that foam comfort properties are not the same at all deflections, and thus performance and perceived comfort will change as a result of the size and shape of the person riding the seat. This research presents information demonstrating the dependence of comfort properties, such as vibrational transmissivity and quasi-static hysteresis, on foam thickness. In addition, the effect of pressure is demonstrated using various masses for the transmissivity testing. Finally, two commonly employed transmissivity test protocols’ results will be compared. This work will be analyzed and discussed from the perspective that comfort properties may need to be defined relative to the sitting pressure of the person riding on the vehicle seat.