Physical vs Virtual testing

While simulation has become a vital development tool, it still can't do everything. But with the high cost of physical acting as a barrier, it seems neither is ideal. Engineering Materials looks at how both are upping their game to offer more.

Despite a clear shift to virtual testing and simulation, testing in the field is still vital, and offers the chance to see if all those design assumptions in office translate to the real world. The clear advantage of digital testing is huge, more tests and variables can be covered virtually at a fraction of the time and cost.

However, for the automotive industry while physical testing has been reduced overall, it continues to be a vital development tool. It gives an opportunity to test real cars with drivers, venues, fuel and transportation, and all the appropriate real world variables. Of course, each adds the associated real world cost onto a development programme so these physical test programmes are normally kept to a minimum, and happen towards the end of a project.

And this leaves open a potential pitfall. If the real world tests do not match up to the simulation prediction, it can delay projects significantly and add substantial cost. But not everyone has to use the same rules in the product development game. And many are exploring alternative routes for testing programme that put the newest technology straight in to some of the harshest real world environments, and do it for a fraction of the cost.

Abingdon-based Zircotec develops ceramic coatings to manage the effects of heat, wear or abrasion on subsidiary equipment. Its plasma-sprayed finishes were initially developed by the UKs nuclear industry. But, these days, they are more likely to be found on a road protecting heat sensitive parts. And it has found this is something becoming increasing prevalent in the automotive industry as OEMs move toward using composite and plastic components. And what is the first thing OEMs ask to see?

"Customers always ask for [real world]test data," says Peter Whyman, sales director at Zircotec. "But, we can't share road car customer's test data as it is proprietary. So, we need data that we can share openly. We realised that some of the race teams we were supplying were logging not only data about the temperature reduction, but crucially, the effects too."

Racing cars on a track, hammering away and pushing everything to limit has proved the perfect test bed for real world testing. The data was initially gathered from the British Touring Car Championship (BTCC) and showed the thermal barrier properties of the coating reduced under bonnet temperature by 37%, and improved the turbocharger response as more energy was retained within the exhaust and not radiated as heat. Buoyed by success, Zircotec started to look for other applications to provide useful physical test data.

"Endurance testing is costly and the real world always throws up more challenging conditions than the lab," says Whyman.

This led to a partnership with Ferrari on its Le Mans Series GTE car. "We got accurate data on how many hours the exhaust had been used for and could therefore monitor any effect on the coating."

Amazingly, Whyman explains it was the exhaust that failed and ultimately needed replacing, while the coating was actually intact.

Virtual tools improve 'black art' engineering

While it is clear manufacturers still demand physical test data, much of the design and development work of engines, chassis, suspension and so on is done virtually, with physical tests only used for checking assumptions and calculations done virtually.

But while the lion share is firmly done in the office, and on the computer, there is one area that remains in the hands of real world development, done by individuals that are often touted as carrying out 'black art engineering and development.'

Tyres is one such area as the simulation of them has remained a challenge. But researchers at the Fraunhofer Institute for Industrial Mathematics have developed a real-time simulation tool called CDTire/3D that might overcome this difficulty.

The software takes into account the heat generated during driving and how the properties of the rubber change over time. The ability to model these various and seemingly random changes has become of greater importance as engineers want to explore more options virtually, in much the same way as other engineered components on the car.

Tyres behave in a complex and non-linear manner, and formulating a calculation that reflects this behaviour is very drawn out, computationally intensive, and cannot be easily incorporated into overall models... and sometimes even them the results provided are inconclusive.

"We have used technology to find a good balance between computation time and accuracy," says Dr. Manfred Bäcker, head of tire and vehicle simulation at Fraunhofer. "Instead of mapping it as a volumetric model, we represent the tyre as a shell, and that saves a great deal of simulation time, yet still takes into account all of the properties."

First, the researchers calculate individual shells for every functional ply of the real tyre: one for every steel belt ply, one for the cap ply, and so on. They subsequently bring these together into a single shell.

So what's so special? The model cleverly takes into account the sidewall as well. In usual simulations, designers need to completely readjust parameters as soon as the tyre width changes or the tyre pressure varies.

"But here, we completely separate geometry from material properties so that you can alter the tyre geometry without having to match the computer model to it," explains Bäcker.

The simulation is already in use worldwide with the likes of Toyota and Daimler, and development is now looking to include temperature into the simulation. This is of particular importance because the tyre is dynamically deformed during driving and because the brakes give off heat. As a result, the tyre warms up and its properties change.

The researchers want to first save the results from CDTire/3D in the temperature model, then with the help of these calculations simulate how the heat travels in the tyres and finally fed these results back into the structural model for an overall picture of material and corresponding tyre behaviour.

"Since the system is modularly constructed, we can couple the temperature model to any simulation tool you want," says Bäcker. "This software can also be employed during the design of an electronic control system like the Electronic Stability Program (ESP)."

Author
Justin Cunningham

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