Type of Document Master's Thesis Author Johnson, Nicholas URN etd-05092011-204328 Title Assessment of Crash Energy - Based Side Impact Reconstruction Accuracy Degree Master of Science Department Mechanical Engineering Advisory Committee
Advisor Name Title Gabler, Hampton Clay Committee Chair Duma, Stefan M. Committee Member Hardy, Warren N. Committee Member Keywords
- crash reconstruction
- delta V
- side impact
Date of Defense 2011-05-03 Availability unrestricted AbstractOne of the most important data elements recorded in the National Automotive Sampling System / Crashworthiness Data System (NASS/CDS) is the vehicle change in velocity, or ΔV. ΔV is the vector change in velocity experienced by a vehicle during a collision, and is widely used as a measure of collision severity in crash safety research. The ΔV information in NASS/CDS is used by the U.S. National Highway Traffic Safety Administration (NHTSA) to determine research needs, regulatory priorities, design crash test procedures (e.g., test speed), and to determine countermeasure effectiveness.
The WinSMASH crash reconstruction code is used to compute the ΔV estimates in the NASS/CDS. However, the reconstruction accuracy of the current WinSMASH version has not previously been examined for side impacts. Given the importance of side impact crash modes and the widespread use of NASS/CDS data, an assessment of the program’s reconstruction accuracy is warranted.
The goal of this thesis is to quantify the accuracy of WinSMASH ΔV estimations for side impact crashes, and to suggest possible means of improving side impact reconstruction accuracy. Crash tests provide a wealth of controlled crash response data against which to evaluate WinSMASH. Knowing the accuracy of WinSMASH in reconstructing crash tests, we can infer WinSMASH accuracy in reconstructing real-world side crashes. In this study, WinSMASH was compared to 70 NHTSA Moving Deformable Barrier (MDB) – to – vehicle side crash tests. Tested vehicles were primarily cars (as opposed to Light Trucks and Vans, or LTVs) from model years 1997 – 2001. For each test, the actual ΔV was determined from test instrumentation and this ΔV was compared to the WinSMASH-reconstructed ΔV of the same test.
WinSMASH was found to systemically over-predict struck vehicle resultant ΔV by 12% at time of vehicle separation, and by 22% at time of maximum crush. A similar pattern was observed for the MDB ΔV; WinSMASH over-predicted resultant MDB ΔV by 6.6% at separation, and by 23% at maximum crush. Error in user-estimated reconstruction parameters, namely Principal Direction Of Force (PDOF) error and damage offset, was controlled for in this analysis. Analysis of the results indicates that this over-prediction of ΔV is caused by over-estimation of the energy absorbed by struck vehicle damage. In turn, this ultimately stems from the vehicle stiffness parameters used by WinSMASH for this purpose. When WinSMASH was forced to use the correct amount of absorbed energy to reconstruct the crash tests, systemic over-prediction of ΔV disappeared.
WinSMASH accuracy when reconstructing side crash tests may be improved in two ways. First, providing WinSMASH with side stiffness parameters that are correlated to the correct amount of absorbed energy will correct the systemic over-prediction of absorbed energy when reconstructing NHTSA side crash tests. Second, providing some treatment of restitution in the reconstruction process will correct the under-prediction of ΔV due to WinSMASH’s assumption of zero restitution. At present, this under-prediction partially masks the over-prediction of ΔV caused by over-prediction of absorbed energy. If the over-prediction of absorbed energy is corrected, proper treatment of restitution will correct much of the remaining error observed in WinSMASH reconstructions of NHTSA side crash tests.
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