Crash tests are always something special – even for the experts. Take this scenario: At 60 km/h, a device with a crash barrier rams into the orange coloured C-Class Mercedes-Benz sedan and hits it full on the side. But this is no usual test programme. The spectacular part of this side impact test is actually located in a frame on the hall ceiling above the vehicle where a linear accelerator serves as an X-ray camera.
Mercedes-Benz along with the Fraunhofer-Institute for High-Speed Dynamics, the EMI (Ernst Mach Institute) based in Freiburg, south-western Germany, Mercedes-Benz has carried out the world’s first X-ray crash with a real car.
For the exercise, on board was one female SID II crash dummy on the left-hand side facing the impact.
This technology demonstration (proof of concept) at the EMI research crash facility in Freiburg has shown that high-speed X-ray technology can be used to visualise highly dynamic internal deformation processes.
Previously, image blurring was an issue and invisible deformations and their exact processes were difficult to ascertain. The numerous, high-resolution images now allow precise analysis and action with the new method.
“The Mercedes-Benz X-ray crash sets a milestone in the development tools of the future. With a direct view into the hidden interior, it can help to draw important conclusions for the further improvement of vehicle safety. Mercedes-Benz thus confirms its role as a safety pioneer in automotive engineering,” said Markus Schafer, Chief Technology Officer and Member of the Board of Management of Mercedes-Benz Group AG.
“The successful X-ray crash provides us with valuable insights to further optimise our technology for capturing previously inaccessible information. Fraunhofer EMI is thus consistently pursuing its strategy of using high-speed X-ray imaging to make dynamic processes visible,” Dr Malte Kurfib, Head of Crash Test Centre, Fraunhofer EMI, says.
Linear accelerator A game changer
So, what’s the breakthrough, one would ask.
In fact, linear accelerators (also known as linear particle accelerators) are not proving to offer wider applications beyond medical treatment as they generate X-rays and high-energy electrons that can be tailored for industrial applications as well.
For several years, the Mercedes-Benz vehicle safety division has been researching the use of X-ray technology in crash tests together with EMI. The decisive factor for the breakthrough was the use of a linear accelerator with 1 kHz technology as the radiation source.
The device is far more powerful than the X-ray flashes previously used in trials: The photon energy of the linear accelerator is up to nine megaelectron volts. This allows all materials commonly used in vehicle construction to be screened easily and the duration of the X-ray pulse is only a few microseconds.
“The world’s first X-ray crash shows that X-ray technology can offer insights. We learn what happens inside a vehicle and to the dummies during an accident. The X-ray images also offer the opportunity to further improve the model quality of the digital prototypes,” says Prof Dr Paul Dick, Director of Vehicle Safety, Mercedes-Benz AG.
Even in this extremely short span, it is now possible to record the deformation processes in the crash test without the motion blur of the past. The linear accelerator also generates a continuous stream of these X-ray pulses. This means that up to 1,000 images per second are possible, which is about 1,000 times as many as with conventional X-ray procedures.
During the crash test, the beams shine through the bodywork and any dummies from above. A flat detector is located under the test vehicle. It serves as a digital image receiver in the X-ray system: When the radiation hits the detector, an electrical signal is generated. The intensity of this depends on how strongly the radiation was previously absorbed by the vehicle and dummy structure. This influences the grey value that is later visible – similar to the X-ray inspection of luggage at the airport or images of this kind taken by a doctor.
Previously, image blurring was an issue and invisible deformations and their exact processes were difficult to ascertain. The numerous, high-resolution images now allow precise analysis and action with the new method.
In the milliseconds of the actual impact time, the X-ray system shoots around 100 still images. Combined into a video, they provide highly exciting insights into what happens inside safety-relevant components and in the dummy’s body during a crash. In this way, it is possible to observe in detail how the thorax of the dummy is pressed in or how a component is deformed. The important part on the way from research to industrial application is the fact that the X-ray crash does not affect any other analysis tools. Even the interior cameras in the crash test vehicle record without any disturbance.
Creating a safe environment
The EMI experts drew up a comprehensive radiation protection concept for the X-ray crash. Dosimetres are used as monitors to ensure that employees are not exposed to radiation. The government authority has approved the operation of the plant in accordance with legal requirements. The elaborate physical protection measures include an additional 40cm-thick concrete wall around the building and a protection door weighing around 45 tonnes.
This feature was first published in Autocar Professional’s May 15, 2024 issue.
