Dept of Aerospace and Engineering Mechanics

Prof. Ala Tabiei

Finite Element Vehicle / Dummy Interaction

Ala Tabiei, Professor of Aerospace Engineering & Engineering Mechanics and Alan McGowan, Graduate Student Center of Excellence in DYNA3D Analysis, Dept. of Aerospace Engineering and Engineering Mechanics University of Cincinnati, Cincinnati, OH 45221-0070

 

Computations were performed using LS-DYNA3D on the Cray T94 at the Ohio Supercomputer Center. The visualizations were done using LS-POST on the Origin2000.

Background and Significance of Work

In recent years, most of the emphasis has been on conducting full-scale tests in order to gain insight into potential safety problems and to develop new and improved roadside hardware. Since the number of vehicles on the roads and the roadside obstacles continue to increase, traffic barrier analysis and design remains am important aspect of public safety. The design of highway hardware (guard rails, sign posts, bridge rails, Light poles, etc.) under vehicle impact are performed experimentally through an iterative process of design, build, test, redesign and retest, until the product meet the design criteria. Recent advancement in computer technology and the availability of cheap and efficient computational power has made it possible to tackle many of the design iterations of such highway hardware numerically.

Experimental evaluation of new or modified highway hardware is expensive and time consuming. On the other hand, numerical simulation of impact behavior of highway hardware under different impact scenarios is cheaper and efficient. It is economically impossible to perform full scale vehicle impact tests on a wide range of parameters. An effective tool in vehicle impact simulation is nonlinear finite element analysis.

Objective of Study

The main objective of the study is to quantitatively determine the effects on an occupant in a pickup/guardrail impact. The areas of focus for the quantitative analysis are Head Injury Criteria and Chest Decelration. Values for these two criterion will be determined using LS-DYNA3D and compared to reasonable values to determine the probability of severe injury. Both belted and unbelted dummies will be used. Figure 1 and Figure 2 show the complete model composed of the NCAC's full size pickup model [1], a dummy, and the G4 (1S) strong post, w-beam guardrail system. This arrangement, minus the dummy, was previously modeled in [2]. Figure 3 shows a close up view of just the cab and dummy. Figure 4 is the same closeup as in Figure 3 with the door removed to show dummy postioning. The dummy, which represents a Hybrid III dummy commonly used crash analysis, was positioned using information from [3]. This positioning was chosen so as to give a more natural seating to the dummy. LS-Post allows for parts to be rendered transparent, hence the pale blue in the side window area. Figure 5 shows a front view of the cab and dummy. This dummy can be clearly seen in Figure 6 and Figure 7.

A model has also been developed using the pickup, guardrail and dummy which contains an unbelted occupant. The results for the belted and unbelted occupant will be compared to see if one configuration provides a higher probability of severe injury.

Figure 8 and Figure 9 show the dummy response to an early stage of the impact. Figure 10 and Figure 11 are later in the impact at a point where the truck is about to flip on it's side.

Additionally, a qualitative study is to be performed to visualize an impact between a sport utility vehicle and a guardrail. The results for the SUV will then be compared with the results from the pickup impact. The model for the guardrail and SUV can be seen in Figure 12 and Figure 13. The results for the SUV and pickup impacts will be compared to see which how different vehicles behave under the same initial condition.

Simulation Platform

These finite element models were developed to test the strong post guard rail system which is the most common system on most highways in the US. The simulation is run on the Cray T94 and Cray T3E at the Ohio Supercomputer center and takes about five days to be completed. The results of the simulation will be compared with full scale crash tests for model validation and finally guard rail system improvement.

References

1. Zaouk, Abdullatif K., Bedewi, Nabih E., Kan, Cing-Dao, Marzougui, Dhafer, Validation of a Nonlinear Finite Element Vehicle Model Using Multiple Impact Data, The George Washington University FHWA/NHTSA National Crash Analysis Center

2. Tabiei, Ala, Wu, Jin Roadmap for Crashworthiness Finite Element Simulation of Roadside Structures, Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati , published in Int. J. Finite Element in Analysis and Design, Vol. 34, No. 2, pp. 145-157, 2000

3. Manary, Miriam A., Reed, Matthew P., Flannagan, Carol, A.C., Scheider, Lawrence, W., ATD Positioning Based on Driver Posture and Position. In Proc. 41st Stapp Car Crash Conference, pp 287-299. SAE Technical Paper 983163. Warrendale, PA: Society of Automotive Engineers, Inc

4. Simunovic, Srdan, Development of a Computational Model for a Sport Utility Vehicle 1997 Ford Explorer XLT, Oak Ridge National Laboratory Modeling and Simulation Group, May13, 1998

Click Here To See Some MPEG Movie Files of Pick-up Crash Simulations