Interaction of the Hand and Wrist with a Door Handgrip During Static Side Air Bag Deployment: Simulation Study Using the CVS/ATB Multi-Body Program 2001-01-0170

This paper presents a parametric study that utilized the CVS/ATB multi-body simulation program to investigate the interaction of the hand and wrist with a door handgrip during side air bag loading. The goal was to quantify the relative severity of various hand and handgrip positions as a guide in the selection of a test matrix for laboratory testing. The air bag was represented as a multi-body system of ellipsoidal surfaces that were created to simulate a prototype seat-mounted thorax side air bag. All simulations were set in a similar static test environment as used in corresponding dummy and cadaver side air bag testing. The occupant mass and geometric properties were based on a 5^th percentile female occupant in order to represent a high-risk segment of the adult population. The upper extremity model consisted of wrist and forearm rotations that were based on human volunteer data. In particular, ellipsoids were added to model the thumb that was needed to simulate the hand engaged in the handgrip. Parameters that were varied included the handgrip length, angle, and spacing, the initial position and orientation of the distal forearm and hand, the inclusion of pronation and supination in the forearm, and the relative motion of the shoulder joint complex. The simulations showed that the inclusion of a handgrip does increase the compressive forearm loading when compared to the matched position, no handgrip simulation. The results also showed sensitivity to initial hand position and wrist orientation with respect to the handgrip. Increasing the length of the handgrip resulted in an increasing trend of peak forearm compressive forces. With regards to the handgrip angle relative to the plane of the armrest, the peak forearm compressive loads were similar in the range of 10° to 45° from the horizontal; however, the forearm compressive loads were lower for the extreme cases of 0° and 90°. Simulations that allowed forearm pronation and clavicle translation resulted in lower wrist loads than those with dummy-like joint properties. Further, the lower loads calculated for the allowed pronation simulation suggests that in order to not over predict loads from ATD testing, pronation may need to be incorporated.