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Modeling and analysis of interactions between occupant, seatback and headrest in rear impact
Published September 11, 1996 by International Research Council on Biokinetics of Impact in Switzerland
The improvement of neck protection in rear impact requires a better understanding of the interactions between occupant, seatback and headrest. A mathematical approach was developed to analyze the interactions and to quantify the influences of different design parameters on neck responses.
The first phase of this development consisted of neck modeling. To begin with, the RID-neck was compared to the Hybrid-III neck in terms of sensitivity with regards to some design parameter changes. A series of mini-sled tests showed the sensitivity of the RID-neck to be better than that of the Hybrid-III neck. Following this preliminary study, a numerica model was developed on the basis of the RID-neck and of two existing sources of biomechanical data on the human neck behavior in rear impact.
For the second phase of this development, the interactions of the thorax and the pelvis with the seatback were modelized, as was that of the head and the headrest. Component tests were conducted to characterize these interactions. With these data, two types of seatback models were constructed. One is a global seatback modeling and the other a more detailed approach which allows the consideration of more design parameters. To evaluate the models, a series of sled tests were performed and the validation level of the above models was assessed against these tests.
Finally, the influences on the neck responses of four design parameters - head-to-headrest distance, seatback-joint stiffness, upper and lower seatback stiffnesses - were analyzed with this model. Special attention was paid to the interactions between these parameters. The results indicate that softening of the upper seatback allows reduction of all neck injury risk indicators and enhances the headrest performance. Softening of the lower seatback increases the moment force at the C7/T1 joint and the head extension angle. Stiffening of the seatback joint aggravates, for a classical upper seatback structure, the moment loading of the neck and the head extension angle. Only the moment force at the C7/T1 joint is significantly affected by all parameter changes.