Distribution of contact pressure and forces between the seated human subjects and a visco-elastic seat is experimentally investigated under vertical vibration. The dynamic pressure on the elastic seat is measured under sinusoidal vertical vibration of different magnitudes in the 1-10 Hz frequency range, using a flexible grid of pressure sensors. The human-seat interface pressure data acquired with a total of six subjects is analysed to illustrate the influence of magnitude and frequency of vibration excitations on the maximum ischium pressure, effective contact area and contact force distribution. The results arc discussed to illustrate the influence of seated posture and the subject build on the contact force and area. Alternately, the contour maps of static pressure distribution, and time histories of the ischium pressure and the effective contact area measured under vibration are compared with those determined while using a rigid seat. The results show that the maximum variations in the ischium pressure and the effective contact area on a soft seat occur near the resonant frequency of the coupled human-seat system (2.5-3.0 Hz). The maximum ischium pressure and effective contact area on a soft seat tend to increase considerably with increase in the magnitude of vibration excitation. (A)
Abstract