Three-dimensional Numerical Model of Free Motion Headform Used in Impact Tests on Vehicle Interior
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THREE-DIMENSIONAL NUMERICAL MODEL OF FREE MOTION HEADFORM USED IN IMPACT TESTS ON VEHICLE INTERIOR Beom-Gyo Seo and Hyun-Yong Jeong* Department of Mechanical Engineering, Sogang University, Seoul 04107, Korea
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(Received 21 January 2019; Revised 14 November 2019; Accepted 9 December 2019) ABSTRACTFMVSS (Federal Motor Vehicle Safety Standard) 201, Standard on Occupant Protection in Interior Impact, requires that the FMH (Free Motion Headform) impact tests result in HIC(d) less than 1000. Especially in the early stage of a vehicle development it is very difficult to conduct the impact tests, so it is necessary to develop a numerical model by which HIC(d) can be predicted. A finite element model for both the FMH and a vehicle can be a good solution, but it needs quite some time and effort to develop such a model. A two-dimensional simple numerical model was developed to predict HIC(d) in the impact tests, but the model does not take into account the impacts where the FMH translates and rotates in three directions. Thus, in this study a new numerical model based on three-dimensional governing equations for the FMH impacting against the interior trim was developed and successfully applied to simulations of the impact tests. KEY WORDS : FMVSS 201, Free motion headform, HIC (Head Injury Criterion), Three-dimensional numerical model
1. INTRODUCTION
center. In addition, a spring connecting between a target point and a point on the circle is used to represent the forcedeflection characteristic of the interior trim at the target point (Deb et al., 2000; Deb and Ali, 2004). However, in the headform impact test, the FMH translates and rotates in three directions because in most cases the line of action of the impact force is off from the CG (Center of Gravity) and the second mass moments of inertia are different with respect to its three axes. Thus, it is very difficult, if not impossible, to predict the kinematics of the FMH during the impact and HIC (d) correctly by using the simple 2 DOF model. Thus, in order to resolve these issues, a threedimensional 6 DOF numerical model was developed in this study. The shape of the FMH in the impact zone and the second moments of inertia were taken into account, and six
According to car accident statistics, about 63 % of all fatalities die of brain damage from car accidents (Chavali et al., 2006). Thus, FMVSS 201 was issued to enforce car manufacturers to reduce HIC(d) (Head Injury Criterion) in FMH (Free Motion Headform) impact tests, which eventually helps the occupants have less brain damage in car accidents. The standard requires to conduct impact tests firing the FMH at a speed of 24 km/h (15 mph) against about 20 target points on the pillars, side rails, headers, roof and any other stiff points in the vehicle interior and resulting in HIC(d) less than 1000 (49 CFR 571.201; U.S. Department of Transportation Highway Traffic Safety Administration, 1998). Needless to say, conducting the tests needs to have an actual vehicle
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