Effect of whole-body vibration and sitting configurations on lumbar spinal loads of vehicle occupants

Whole-body vibration (WBV) has been identified as one of the serious risk factors leading to spinal disorders, particularly in professional drivers. Although the influential factors in this area have been investigated epidemiologically, finite element (FE) modeling can efficiently help us better understand the problem. In this study, a modified HYBRID III dummy FE model which was enhanced by detailed viscoelastic discs in the lumbar region was utilized to simulate the effect of WBV on lumbar spine loads. Spinal responses to the vertical sinusoidal vibrations of a generic seat were obtained and spinal injury risk factors were calculated. Effects of variation of excitation frequencies, three different seatback inclinations and four pre-defined occupant postures on the spinal loads were investigated as influential variables. Results showed that under sinusoidal loading with a frequency of 5 Hz and in a typical sitting configuration, disc forces remained in a safe range (< 1700 N) for short term. Collagen Fibers strain ( < 0.3%) and intradiscal pressure ( < 1.15 MPa) also indicated that the spinal loads were in a safe range. Additionally, calculating the risk factor according to ISO 2631-5 (about R = 0.8) confirmed the low probability of an adverse health effect due to WBV in long term. Frequency-domain analysis showed the resonance frequency to be at f = 6.27 Hz. Although according to ISO/CD 2631-5 standard, the occupant experienced the highest risk of injury at f = 7 Hz, it was found that spinal compression load at f = 6 Hz was 7.7% higher than the compression load at f = 7 Hz. Seatback oriented at 75 degrees exhibited the highest risk of injury, nevertheless, maximum von-Mises stress in disc annulus was observed at 70 degrees. In the evaluation of occupant posture, lordotic and slouching postures were compared and the latter exhibited higher stress ranges resulting in higher injury risk factor. Results of the model demonstrated its aptness to predict the spinal disc injuries in response to various vibrational loading and boundary conditions.