InTrans / Sep 09, 2007
Crashing for a living
posted on September 9, 2007
A NASCAR race car flies down the 3,000-foot runway, propelled by 2 pickup trucks using a pulley system. A 100 foot long curved steel and foam barrier waits at the end. The car reaches 100…120…130…140 miles per hour. The tow cables release from the car. Smash! The race car slams into the wall. The car is crushed on the front and side. The wall has some scrapes and dents and smashed foam energy absorbers. Everyone’s pleased. After the crash, engineers inspect the wall and the car. The team is researching the Steel and Foam Energy Reduction barrier, better known as the SAFER barrier installed on NASCAR and Indy Racing League (IRL) racetracks.
In a race, the foam energy absorbers would be replaced after such a severe hit. (The cars are designed to crush and absorb the energy of a crash so drivers aren’t hurt.) The SAFER barrier is already installed on the tracks, but the engineers are always looking for ways to make it better. “We’re looking for tearing or snagging, catching on the vehicle. We don’t want the car or barrier to rip,” says Curt Meyer, the research engineer who helped set up and conduct the test at the Midwest Roadside Safety Facility (MwRSF) at the University of Nebraska-Lincoln. The researchers also collect a lot of data during the test that they’ll spend weeks analyzing. Here’s how they get it:
- An instrumented dummy that looks like a person sits in the front seat and measures how a driver would be affected.
- A speed trap system tells the engineers exactly how fast the car was moving at impact.
- High-speed digital cameras shoot the crash from different angles inside and outside of the car to analyze the vehicle and barrier motions.
- Inside the car, several accelerometers record the acceleration and forces on the vehicle during the crash. A rate gyroscope measures the car’s rotation.
Since the SAFER barrier has been installed on NASCAR and IRL racetracks, no drivers have died or been seriously hurt from hitting the wall. “The SAFER barrier is a “big’ guardrail for the race league,” says Bielenberg.
The university researchers don’t only work on racing barriers. They spend most of their time keeping us safe by designing and testing guardrails, median barriers, and bridge rails. Dean Sicking, director of the MwRSF at the University of Nebraska-Lincoln, was one of the first designers of energy-absorbing end terminals for guardrails.
“It used to be that if a car hit the end of a guardrail, then the guardrail could cut the car like a knife through butter,” says Bob Bielenberg, research engineer at the MwRSF.
Now the end terminals absorb the energy of the crash and bring the car to a stop. The university estimates that 600:700 lives are saved each year because of these end terminals. These engineers know that crashes happen, so they study how vehicles and barriers interact to keep people alive when they do.
Crashing a car into a wall or guardrail isn’t the only way to see how a barrier reacts to a collision. Researchers like Bob Bielenberg do it with computer modeling.
“I like to say computer modeling for crash testing isn’t that far removed from what animators did for Shrek,” Bielenberg says.
For example, in Shrek, animators told the computer how a person’s hair moves. Then, let’s say there’s a scene with Princess Fiona where they want the wind to come from the east. The computer has already been told how hair moves. All the animators have to do is tell the program the wind is coming from the east to generate realistic-looking hair movement.
With crash testing, Bielenberg draws the vehicle and barrier in a 3D software program and breaks the parts up into thousands of small pieces called elements. Then he tells the computer what the elements are made of. If they’re steel, then he tells the computer that steel has a certain strength, weight, etc. He does this for each element. After defining each element, he tells the computer how they’re connected to each other and applies motions and loads to the model. After the model is defined, the computer simulates the crash test. He gets to see what should happen when a real car is crashed into the real barrier.
“In a model we can be anywhere we want and measure anything we want,” he says.
Sometimes they’re surprised when they run a physical test.
“Every problem has an answer in the classroom. But here we come up with an answer and then test it. Sometimes we’re not even close, and we have to try something different,” Bielenberg says. “People would like modeling to replace tests, but I don’t think that’s going to happen. What they can do is greatly reduce the number of tests you have to run. We can get to an answer much quicker and get a better answer. But I don’t think we ever want to leave people’s safety up to a computer.”
About the job
You might think you have to be a professor to work at a university. But actually lots of people who work at university research centers aren’t professors. The full-time research engineers at the MwRSF (http://engineering.unl.edu/), including those who do computer modeling, have at least four year degrees in either civil or mechanical engineering. They often have master’s degrees, the two year degree following a bachelor’s. They work closely with faculty on their projects but spend their time on the research projects rather than teaching classes like professors.
Crash testing is also done by private companies that sell safety equipment like guardrails and work zone barriers to cities and state departments of transportation. A four year degree in civil or mechanical engineering would also be required to work for these companies.
“I think it’s a really fun job,” says Meyer. “I’m big into motorsports.”
By Rema Nikalanta