Wang 1 ACCURACY OF VEHICLE FRONTAL STIFFNESS ESTIMATES FOR CRASH RECONSTRUCTION

The National Highway Traffic Safety Administration (NHTSA) estimates delta-V from detailed measurements of vehicle deformation using the WinSMASH crash reconstruction code. Previous research has shown that WinSMASH delta-V estimates underpredict true delta-V by 25% on average. One possible explanation for this error is inaccuracies in the stiffness values used in the deltaV reconstruction calculation. The accuracy of codes, such as WinSMASH, is dependent upon vehicle stiffness values computed from post-impact crush measurements in crash tests. Any error in these crush measurements will be reflected as inaccuracies in the stiffness coefficients, and ultimately as errors in WinSMASH delta-V estimates. This paper investigates the accuracy of post-impact crush measurements in 93 frontal New Car Assessment Program (NCAP) tests of model year 2005-2007 vehicles. INTRODUCTION AND BACKGROUND Estimating the total change in velocity or delta-V of a vehicle during a crash is a way to evaluate the severity of a motor vehicle accident. The calculated delta-V can be used as an important parameter to study the occupant injuries resulting from the crash. Therefore, the fidelity of these studies will be affected by the accuracy of the delta-V estimations. NHTSA uses WinSMASH, a derivative of CRASH3 to estimate the delta-Vs of real-world crashes through post-crash reconstruction [1]. The algorithm of CRASH3 [2] was based on the work done by Campbell in which a linear relationship was observed between static crush and impact speed into a fixed rigid barrier [7]. The delta-V calculation is based on the estimation of the absorbed crush energy by the vehicle from the post-crash measurements of the vehicle deformation. The damage algorithm in WinSMASH uses the post-crash measurements of the vehicle to estimate the energy absorbed by the vehicle in the approach phase of the crash, which is then used to estimate the delta-V by applying the Newton’s second law of motion and conservation of linear momentum. Previous research has shown that WinSMASH deltaV estimates underpredict true delta-V by 25% on average [3, 1, 4, 5]. One possible explanation for this error is inaccuracies in the stiffness values used in the delta-V reconstruction calculation. The accuracy of codes, such as WinSMASH, is dependent upon vehicle stiffness values computed from post-impact crush measurements in crash tests. Any error in these crush measurements will be reflected as inaccuracies in the stiffness coefficients, and ultimately as errors in WinSMASH delta-V estimates. Calculation of Delta-V Equation 1 and Equation 2 are used by WinSMASH to calculate delta-V for one of the simplest collision configurations, a central collision, which is defined as a collision where the line of action of the collision forces passes through the centers of mass of the two vehicles. For the frontal vehicle crash with a rigid barrier, Equation 1 and Equation 2 can be simplified to Equation 3.