FULL-WIDTH AND OFFSET FRONTAL CRASH ANALYSIS OF A FORD TAURUS AND CORRESPONDING OCCUPANT RESPONSES

ABSTRACT

         Safety is of paramount importance to manufactures of roadway vehicles. Although much progress has been made in the field of passenger safety in a car in the last years, there is still a strong need for the design of a more crashworthy vehicle in a frontal collision. In this research, a Ford Taurus model is analyzed in a frontal full-width and offset impact. This paper describes the results of a non-linear finite element computer simulation in LS-DYNA using a Ford Taurus model in a frontal collision for a full width rigid barrier and an offset deformable barrier. Finally the responses of an occupant for the above crash tests are analyzed using the Mathematical Dynamic Modeling (MADYMO) code. The full-width and offset crash test results are compared and the results showed that in both the cases there is no injury to the head. But in the offset crash test the results showed that there is severe leg injury.

INTRODUCTION

Today’s passenger vehicles are designed with more crashworthy than ever before. But still in overall crashes most of the passenger vehicle occupants die in frontal crashes. More than 30,000 people die in crashes on US roads every year. So the design for a more crashworthy vehicle is always a necessity to reduce these deaths. The injury to a passenger also depends on how well the vehicle is equipped with occupant restraint systems. So the level of safety performance of the vehicles has to be assessed. Federal Motor Vehicle Safety Standard (FMVSS) 208 specifies performance requirements for the protection of vehicle occupants in crashes. Every year the National Highway Traffic Safety Administration (NHTSA) buys brand new cars right off the lots and crashes them. This is done to compare how well different vehicles protect front-seat passengers in a head-on collision.

         The NHTSA’s protocol, FMVSS 208 involved running vehicles head-on into a fixed barrier at 35 mph. Results were published for the information of consumers, as the US arm of the international New Car Assessment Program (NCAP). Figure 1 shows the setup for the NCAP testing method. In the Insurance Institute for Highway Safety’s (IIHS) 40 mph offset test, 40 percent of the total width of each vehicle strikes a barrier on the driver side. The barrier's deformable face is made of aluminium honeycomb, which makes the forces in the test similar to those involved in a frontal offset crash between two vehicles of the same weight. Figure 2 shows the setup for the IIHS testing method.

Figure 1. NCAP test setup

Figure 2. IIHS test setup

CRASH ANALYSIS OF FORD TAURUS

         The FE model of Ford Taurus is divided into 123 parts. These parts represent the components of the vehicle. Out of the 123 parts, 104 parts are used with shell elements to model the sheet metal components, 18 parts are assigned beam elements to represent the steel bars in the vehicle and one part is modeled with brick elements to represent the radiator.

         The detailed finite element model of Ford Taurus model is crashed onto a rigid barrier, full-width at 35mph according to NCAP regulations. The barrier is developed in PATRAN and the relative properties are assigned to make it rigid.  Offset barrier crash tests are conducted at 40 mph and 40 percent overlap. The test vehicle is aligned with the deformable barrier such that the right edge of the barrier face is offset to the left of the vehicle centerline by 10 percent of the vehicle’s width.

Figure 3.Full-Width Crash

Figure 4. Offset Crash test

Crash Test

         In the full-width test the total crash energy is absorbed by the full frontal structure. Crashing the full width of a vehicle into a rigid barrier maximizes energy absorption and the integrity of the occupant compartment is maintained. Figure 5 shows the deformation in the front structure in a full-width crash. Figure 6 shows the deformation of the front structure in an offset crash.

Figure 5. Full-width crash

Figure 6. Offset crash

Figure 7. Occupant compartment in offset crash

DEVELOPMENT OF OCCUPANT VEHICLE MODEL IN MADYMO

         To evaluate the occupant impact response the car interior is modeled in MADYMO computer code. The occupant compartment of Ford Taurus car is modeled in MADYMO with the measurements taken from the finite element model of the car and also from the actual car. The driver is the 50^th percentile Hybrid III male dummy.

Figure 8. Occupant vehicle modeling in Madymo

OCCUPANT IMPACT RESPONSES IN MADYMO

The occupant responses in the full-width and offset crash tests are evaluated. The acceleration pulse is derived from the LS-DYNA simulation of the FE Ford Taurus model. Occupant responses are evaluated by using the injury criteria given by the MADYMO program.

Figure 9. Occupant responses for offset crash pulse

Table 1. Occupant injury responses in full-width

Table 2. Occupant injury responses in offset

Figure 10. Simulation results of footboard intrusion in offset

Tibia index measures combined bending and compression forces on the lower leg and an index reading of 1 or more represents an unacceptably high risk of tibia fracture. As it is observed there is severe injury to the lower right tibia in the offset crash test as the peak value is above 1. The lower left tibia index is also high when compared to the upper part of the tibia. The lower tibia of both the legs have high injury risk in an offset crash when compared to the full-width crash. Figure 10 shows the simulation results.

CONCLUSIONS

         In both full-width and offset crash tests there is no severe injury to the head, chest and lower torso. The head and chest injury parameters are higher in the case of the full-width test when compared to that of offset. In full-width there are higher occupant compartment decelerations so they are especially demanding of restraint systems but the integrity of the compartment is maintained. In offset test as only part of the front structure takes the crash energy there is intrusion into the occupant compartment. So the bottom line is that full-width test are especially demanding of restraints but less demanding of structure, while the reverse is true in offsets. The intrusion of the occupant compartment is simulated in MADYMO and the injury to occupant lower extremities is evaluated. In offset test, there are an unacceptably high tibia index values for the lower tibia that shows  severe leg injury.  

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