Mercedes-Benz X-rays a crash test as the world's first automaker

The technical sensation begins with a very loud bang: at 60 km/h, a device with a crash barrier rams the orange C-Class limousine and hits it squarely on the side. Crash tests are always something special – even for the experts. But the truly spectacular aspect in this side crash test is located in a frame on the ceiling of the hall above the vehicle: a linear accelerator serves as the X-ray source.

Together with the Fraunhofer Institute for High-Speed Dynamics – Ernst-Mach-Institute (EMI) in Freiburg, Mercedes-Benz has now conducted the world's first X-ray crash test with a real vehicle. On board were two SID IIs model dummies on the impact-facing left side. These are test bodies with female anatomy, specifically designed for side impact tests.

Depicting highly dynamic internal deformation processes

With short-term X-ray technology, highly dynamic internal deformation processes can be depicted, as demonstrated by this proof-of-concept at the EMI research crash facility near Freiburg. Previously invisible deformations and their exact sequences thus become transparent. The numerous high-resolution images allow for precise analysis.

"The X-ray crash by Mercedes-Benz sets a milestone for the development tools of the future. It can help draw important conclusions for further improving vehicle safety through a direct look into the hidden interior," said board member and CTO Markus Schäfer of the Mercedes-Benz Group.

Short-term X-ray technology: Up to 1,000 images per second

For several years, the vehicle safety division of Mercedes-Benz has been researching the use of X-ray technology in crash tests together with colleagues from EMI. The breakthrough was achieved by using a linear accelerator with 1-kHz technology as a radiation source. The device is far more powerful than the previously experimentally used X-ray flashes: the photon energy of the linear accelerator is up to nine megaelectronvolts. This allows all materials commonly used in vehicle construction to be penetrated. The duration of the X-ray pulse is only a few microseconds. This allows deformation processes in crash tests to be recorded without motion blur. In addition, the linear accelerator generates a continuous stream of these X-ray pulses. This makes up to 1,000 images per second possible, which is about 1,000 times as many as conventional X-ray methods.

Still images compiled into a video

During the crash test, the rays illuminate the body and any dummies from above. An X-ray detector is located under the test vehicle. It acts as a digital image receptor for the X-ray system: when the radiation hits the detector, an electrical signal is generated. The intensity of this signal depends on how much the radiation was previously absorbed by the vehicle and dummy structure. This affects the grayscale value later visible – similar to the X-ray inspection of luggage at the airport or corresponding images at the doctor's office.

During the actual impact time of one-tenth of a second, the X-ray system captures about 100 still images. Compiled into a video, they provide highly interesting insights into what happens inside safety-relevant components and the dummy's body during the crash. This allows detailed observation of how the dummy’s thorax is compressed or how a component deforms. Important for the transition from research to industrial use: the X-ray crash does not affect other analytical tools. The interior cameras of the crash test vehicle also record without interference.

Comprehensive radiation protection concept

For the X-ray crash, EMI specialists have developed a comprehensive radiation protection concept. Dosimeters are used to monitor that employees are not exposed to any radiation. The government authority has approved the operation of the facility according to legal requirements. The elaborate physical protection measures include an additional 40 cm thick concrete wall around the building and a radiation protection door weighing about 45 tons.