Characterization of Vehicle Occupant Compartment Material Properties Using MADYMO: Methodology and Validation

During a motor-vehicle collision, an occupant may interact with a variety of interior structures. The material properties and construction of these structures can directly affect the occupant's kinetic response. Simulation tools such as MADYMO (Mathematical Dynamical Models) can be used to estimate the forces imparted to an occupant for injury mechanism and causation evaluation relative to a particular event. Depending on the impact event and the specific injury mechanism being evaluated, the selection of proper material characteristics can be quite important. A comprehensive literature review of MADYMO studies illustrates the prevalent use of generic material characteristics and the need for improved property estimation and implementation methods. Vehicle safety compliance tests for occupant protection (Federal Motor Vehicle Safety Standard (FMVSS) 201, or FMVSS 201, published by the National Highway Traffic Safety Administration (NHTSA) were collected and analyzed for a variety of vehicles. These tests include localized head impacts to the instrument panel and the upper interior. Comparison of matched points between different vehicle types illustrates considerable differences and variability, despite common design and regulatory compliance goals. Average and statistical ranges of force-deflection characteristics of vehicles were calculated and are presented for the purpose of modeling when generic models are appropriate. However, due to this inter-vehicle variability, a methodology was developed simulating individual NHTSA FMVSS 201 test results within MADYMO and optimizing the simulated material properties to produce correlated occupant responses. This method was developed and validated for headform impacts to specific locations, but may also be applied to validate other interior contact areas using matched test data such as thoracic impacts to the steering column.