"Crash Course," Feature Article, December 2007

FEATURE FOCUS: BIOENGINEERING

crash course

The test dummy in a virtual world.

by Harry Hutchinson, Executive Editor

there's a cartoon by Gary Larsen called "Night of the Crash Test Dummies." It shows a group of dummies that have come to life and are getting their revenge by shoving lab technicians into a test car.

It's not the only crash test dummy joke, though it may be the only one that's the title of a book. After all, the dummy's almost-human appearance seems to be begging for a punchline.

A crash test dummy is made of plastic and metal designed to register the shocks that flesh is heir to. It is the stand-in representing human frailty caught in the unfortunate clash of machines. Dummies and the thousands of wrecked prototypes they have occupied are the reason we are so much safer on the road now than we were 20 years ago.

To keep the momentum going, and perhaps to cut down on the sheer number of vehicles to be sacrificed, the German Association for Automotive Research, an organization of German carmakers, their suppliers, and a manufacturer of dummies, is supporting a project to create a digital test subject so additional crash scenarios can be studied in computer simulation.

Although a crash test dummy tries to approximate human flesh, bones, and joints, the software developers aren't doing exactly that. Instead of approximating you or me, they are creating digital models of the dummy.

A French company, ESI Group, announced that it has released Version 2.0 of BioRID-II for its PAM-Crash/PAM-Safe 2G simulation software. BioRID stands for "biofidelic rear impact dummy."

Shot in the back: A digital crash test dummy permits additional testing for automobile safety without having to wreck prototypes. Software companies are developing models of BioRID-II.

ESI's model corresponds to the second generation of a dummy that helps make cars safer during rear-end collisions. ESI is not alone. Marc Shrank, director of crashworthiness and occupant safety for the Simulia unit of Dassault Systèmes, said the company expects to have a digital BioRID-II of its own soon for use with its analysis software, Abaqus. A German company, DYNAmore GmbH, is working on a model for use with LS-DYNA software.

The models recreate for the computer the features of the physical dummy. The physical BioRID-II has an articulated human-like spine with the requisite two dozen vertebrae. The dummy has a pretension load on the neck held by a single damper mounted in parallel with a flexor and an extensor spring. The dummy's abdomen is filled with a water cavity and the torso texture is soft silicon rubber. The models recreate these features for computer analysis.

According to Peter Ullrich, ESI Group's crash safety and impact product manager, manufacturers use the dummy to enhance seat-frame structure so that it will absorb more energy in a crash and cut down on rebound effects.

The purpose of the virtual crash test dummy, as with all finite element models, is not to replace physical testing but to supplement it. Numerous tests can be made in a computer without having to build a physical prototype for each case and, in this application, to destroy it. Instead, ideas can be tested in complex mathematical models in the computer, and then the most promising can be replicated as physical experiments.

There's a reason that the computer models mimic the dummy instead of trying to go straight to the source and represent a living human. Shrank and other experts say it is to make results of computer simulations comparable to the physical experiments.

The manufacturers' association, also known as FAT, for its name in German, Forschung Automobil Technik, is composed of representatives of Germany's leading car brands—Audi, BMW, DaimlerChrysler, Karmann, Opel, Porsche, and Volkswagen. Also involved are seat manufacturers Hammerstein, Johnson Controls, and Keiper, and the maker of the crash dummy, Denton COE.