The Interaction of Air Bags with Upper Extremity Test Devices

This study examines and compares the response of two upper extremity test devices under driver-side air bag deployment to contribute to the development of dummy surrogates for the investigation of primary contact forearm injuries during air bag deployments. The first of these test devices, the SAE 5’ Percentile Female Arm (SAE Arm), is an anthropomorphic representation of a small female forearm and upper arm that is instrumented with load cells, accelerometers and potentiometers to enable the determination of upper extremity kinematics and dynamics. The second, the Research Arm Injury Device (RAID), is a simple beam test device designed for detailed investigation of moments and accelerations resulting from close contact in the initial stages of air bag deployment. The RAID includes strain gauges distributed along its length to measure the distribution of moment applied by the air bag deployment. The study used four air bags representing a wide range of aggressivities in the current automobile fleet. The upper extremity position was a ‘natural’ driving posture when turning left with one hand across the steering wheel. The forearm was positioned directly on the air bag module with the forearm oriented perpendicular to the air bag module tear seam. For the SAE Arm, the humerus was oriented normal to the steering wheel. Tests with the SAE Arm were performed both with the arm attached to a 5’ Percentile Female Hybrid III dummy and with the arm mounted to a universal joint test fixture. TheRAID was mounted to an articulated test fixture. In addition to the dynamic tests, a detailed comparison of the inertial properties of each of the test devices with the inertial properties of a typical small female was performed. Forearm response from both test devices confirmed the levels of air bag aggressivity determined using previous cadaveric injury results. In addition, logistic risk 1628 functions for forearm fracture were developed using existing cadaver studies and the moment response of each test device. These risk functions indicate that for 50% risk of ulna or ulna/radius fractures, the SAE arm peak forearm moment is 61 N-m (+/13 N-m standard deviation) while the RAID peak forearm moment is 373 N-m (+/83 N-m standard deviation). For 50% risk of fracture of both the ulna and the radius, the SAE arm peak dummy forearm moment is 91 N-m (+/14 N-m standard deviation) while the RAID peak forearm moment is 473 N-m (+/60 N-m standard deviation).