Study of Vehicle Dynamics and Occupant Response in Side Impact Crash Tests
Side impact crash is a leading cause of fatalities on the roadways of the industrialized world. In the mid 1990's NHTSA implemented a new car assessment program testing the lateral crashworthiness of vehicles entering the market with a moving deformable barrier. Previous work has been done in an attempt to distill these tests into finite element simulations using specific vehicle test results; however there has not been a comprehensive study attempting to develop a model that includes a large number of tests to evaluate trends in vehicle kinematics and how they affect the occupants coupled with finite element simulations. To this end, a study of side NCAP tests was performed on all sedan cars based on the test results reported in the NHTSA Vehicle Crash Test Database since the introduction of the 2005 model year. This data was used to evaluate typical motion of the target vehicle during a regulatory crash test, and the corresponding occupant response. This sample consisted of new models entering the market and nameplates with major redesigns with a sample size of 72 vehicles. From these tests a series of velocity profiles were developed including time versus average velocity plots for vehicle center of gravity, door sill, driver's seat and driver door. These parameters have been shown to be important in occupant response and injury. There was significant variability in the response at several accelerometer locations. It was also found that rotation of the vehicle did not become significant until after 100 ms, after the maximum injury was predicted by the dummy. A parametric finite element analysis was performed using the both the USSID and ES-2re models to study the response of a restrained occupant during a typical crash test. These simulations showed that the velocity of the intruding door had a large effect on the thoracic injury predicted by the side impact dummy models. The full text of this paper may be found at: http://www-nrd.nhtsa.dot.gov/pdf/esv/esv21/09-0016.pdf For the covering abstract see ITRD E145407.
Explicit finite element method applied to impact biomechanics problems
Biofidelic numerical models require accurate geometry, material properties, representative loading conditions, and proper verification and validation based on relevant experimental studies. Imaging techniques such as CT or MRI are typically used to generate anatomically correct model geometry. Accurate biological material properties and constitutive models present a challenge since tissues are typically anisotropic with nonlinear viscoelastic behavior and must be represented using a continuum approach. Verification and validation is a crucial development step to demonstrate the biofidelity of the model against experimental studies and is differentiated from model calibration, which involves adjusting FE modeling parameters to improve the agreement between the model and experimental data. Validation of the model should be performed in a continuous stepwise process, with increasing levels of complexity. Evaluating a numerical model against a variety of different loading conditions is the best means to obtain a fully validated model and this should be considered as a continuous process throughout the useful life of the model.
A fundamental look at side impact
This paper analyzes side impact data using a method based on the velocity - time history of several key points in the colliding vehicles. This method exhibits on a single graph the relationship between structural modifications, interior padding, intrusion, change-of-velocity of the struck car door, and human injury criteria. Using the model to analyze a side impact with a dummy and one matched collision with a cadaver, it appears that this method is compatible with current side impact injury levels.