"Without actually simulating the effects on the occupant, we can still can evaluate measures that affect their safety in a front-impact crash," says Bob Mayer, Staff Research Engineer in the Product Development Methods group of the Vehicle Analysis & Dynamics Lab. "One is structural intrusion - for example, how much the floor pan moves in. The other is effective acceleration, which needs to decrease to produce a softer pulse for the occupant."

Unfortunately, there's usually a tradeoff between the two: If engineers make the pulse very soft, the structure won't absorb enough energy to limit intrusion. And if they limit intrusion to almost none, the pulse will be hard. But the extendable bumper is a rare case where both can be reduced, because of the increase in crush space.

"To analyze the bumper, we essentially extended the rail that was already there," explains Mayer. "We built a finite element model and then used a crash analysis code called LS-DYNA3D to run the model. The code determines how much energy is absorbed when the structure bends, what will happen when it contacts other parts contact each other, what the mass is, and other parameters."

Simulating a front-impact crash at 30 mph, the researchers determined that intrusion at a specific location was reduced from 71 mm to 40 mm (44 percent) and effective acceleration was reduced from 22.9 to 19.2 gs, as shown in Figure 2. Increasing the crush space at the front of the vehicle results in less intrusion and a softer pulse in a crash - an optimal combination that makes the vehicle much safer wherever the occupants are seated.

30 mph Frontal Barrier	Intrusion (mm) (% Reduction)	Eff. Accel. (g's)	Mass (kg)
Baseline	71.3 (0 %)	22.9	1385.9
Extendable Bumper	39.9 (44%)	19.2	1387.5

Figure 2. Extendable Bumper Analysis

Safety Car Showcases Team Innovation

Analysis of the Cross-car Beam