Refinement and Validation of a Three-Dimensional Head-Spine Model

A three dimensional discrete model of human spine, torso and head has been refined and validated by comparison with available experimental results. The model consists of a system of rigid bodies, representing the head, vertebrae, and ribs, interconnected by deformable elements which represent the intervertebral discs, ligaments, and other connective tissues. Four models of varying orders of complexity have been developed, ranging from a complex model to a very simplified model with 32 degrees of freedom. The simplified model is able to closely reproduce many of the response characteristics of the more complex models in G sub z loadings, and, because of its simplicity and short running time, may be well suited for design use. Experimental results for human subjects suitable for validation of models are primarily available in the form of impedance curves for vertical harmonic excitation so techniques were developed which efficiently obtain impedance curves for the model. Comparisons of the impedance curves show good agreement, both in the magnitudes and locations of peaks. Furthermore, it was shown that the primary peaks in the impedance curve in the 5 to 7 Hz range result from a combination of buttock-seat resonance, the flexural response of the spine and visceral resonance. Analogous head-spine models were developed for the chimpanzee, baboon, and rhesus monkey. The objective of this development was to provide a scaling methodology for dynamic response and injury data among these non-human primates and man. Impedance curves are presented for these models and show significant differences in character from that of the human spine models.