Crash Test Dummies Go Digital

The traditional way to test vehicle designs is by creating physical prototypes.

However, each one can cost as much as $750,000 and take four months to build. Digital prototypes aim to cut cost and design times by accurately simulating real-world crash performance and reducing the need for physical prototypes

By law, cars have to undergo crash testing before they can be sold to the public, and carmakers traditionally designed new models to meet ; rather than exceed -- safety requirements.

This situation changed dramatically in the 1990s when safety became an important marketing weapon.

Today, using computer-aided engineering (CAE) software running on supercomputers, carmakers can accurately model the real-world performance and crash behaviour of designs before any prototypes are built. This shortens design times and allows for quicker response to market trends.

"With the shortening of design cycles, crash simulation is a crucial competitive issue for car manufacturers," says Thierry Bertucat, spokesman for ESI, a French software company that claims to be the leader in crash simulation software.

ESI began working in this field in 1985 when it teamed up with Volkswagen to develop simulation software for analysing the severe deformations inflicted on a car as a result of a crash. This was the first step toward the development of ESI's flagship product Pam-Crash, which is now used by most carmakers.

The software allows simulations to be carried out much earlier in the design process, so reducing the need for modifications later.

At an early stage in the design process, the cost of making changes is relatively low. Once the carmaker commits to a particular design and builds the first physical prototype, the cost of changes rises considerably. If a change has to be made once the production tooling has already started, the cost of a design change can be enormous.

Volkswagen uses Pam-Crash software to test its virtual cars in various crash scenarios according to the legal requirements of different countries as well as specialised tests devised by car magazines or associations.

Crash testing is a particularly demanding application for a computer because of the huge number of calculations that need to be performed to accurately simulate the deformations created by an impact on the structure of a car.

Crash simulations are thus a compromise between accuracy and response time -- the most accurate results can tie up a supercomputer for days on end.

Volkswagen has long used NEC supercomputers for this task and the most recent model installed, the NEC SX-5, has 12 processors, each with a peak performance of four gigaflops.

Despite the move to a faster supercomputer, it still takes 12 hours to run a crash simulation using Pam-Crash -- the program is typically left running all night.

Rather than using the new computer's extra power to speed up the simulations, Volkswagen has used it to create a finer grid -- the mesh of points that the computer uses to simulate the 3-D shape of the car surface using a technique called finite element analysis (FEA).

To model a crash between two vehicles, the supercomputer may have to analyse 250,000 individual elements. The simulations needed for the highly critical air bag sensors are even more demanding.

Despite the growing use of virtual prototypes, no carmaker feels confident enough to abandon the traditional practice of crashing physical cars in favour of computer-based simulations.

Sent in by Pete Frost