Application of a Finite Element-Based Human Arm Model for Airbag Interaction Analysis

Interaction of the human arm and deploying airbag has been studied in the laboratory using post mortem human subjects (PMHS). These studies have shown how arm position on the steering wheel and proximity to the airbag prior to deployment can influence the risk of forearm bone fractures. Most of these studies used older driver airbag modules that have been supplanted by advanced airbag technology. In addition, new numerical human body models have been developed to complement, and possibly replace, the human testing needed to evaluate new airbag technology. The objective of this study is to use a finite element-based numerical (MADYMO) model, representing the human arm, to evaluate the effects of advanced driver airbag parameters on the injury potential to the bones of the forearm. The paper shows how the model is correlated to Average Distal Forearm Speed (ADFS) and arm kinematics from two PMHS tests. The PMHS testing employed different offsets (0 and 25mm) between the airbag and forearm in a driving position, using the two arms of the same human subject. The model is then exercised to determine predictive ability for forearm fracture seen with the 0mm offset test, but not seen with the 25mm offset. The model accurately predicts fracture in the 0mm offset test, and no fracture in the 25mm offset test using a ADFS criterion of 10.5 m/s. Model elements in the ulna that rapidly exceed an arbitrary 1% effective strain criteria correspond to fracture locations on the ulna of the 0mm offset PMHS test. The model is then exercised to predict fracture using the ADFS criterion for multiple inflator outputs. The paper also discusses issues and recommendations for human model parameters to further increase the robustness of the model.