Maximum Transparency: Mercedes-Benz Is the World’s First Car Manufacturer to X-Ray a Crash Test

The technical sensation begins with a loud bang. At 60 km/h, a device with a crash barrier rams into the orange C-Class saloon and hits it full on the side.

Crash tests are always special—even for the experts. However, the spectacular part of this side impact test is located in a frame on the hall ceiling above the vehicle: A linear accelerator serves as an X-ray camera.

With the Fraunhofer Institute for High-Speed Dynamics and the EMI (Ernst Mach Institute) in Freiburg, Mercedes-Benz has now carried out the world’s first X-ray crash with a real car. On board was one SID II dummy on the left-hand side facing the impact. This test specimen, with female anatomy, is specially designed for side impact tests.

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 invisible deformations and their exact processes thus become transparent. The numerous, high-resolution images allow precise analysis.

Ultrashort X-Ray Technology

For several years, the Mercedes-Benz vehicle safety division has been researching the use of X-ray technology in crash tests with colleagues from EMI. The breakthrough’s decisive factor was using a linear accelerator with 1 kHz technology as the radiation source.

The device is far more potent 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.

The duration of the X-ray pulse is only a few microseconds, making it possible to record deformation processes in the crash test without motion blur. The linear accelerator also generates a continuous stream of these X-ray pulses, meaning up to 1,000 images per second are possible—about 1,000 times as many as 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 is 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.

In the milliseconds of the actual impact time, the X-ray system shoots around 100 still images. Combined into a video, they provide fascinating 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 dummy’s thorax is pressed in or how a component is deformed. The critical part of the way from research to industrial application is that the X-ray crash does not affect other analysis tools—even the interior cameras in the crash test vehicle record without disturbance.

The EMI experts developed a comprehensive radiation protection concept for the X-ray crash. Dosimeters are used as monitors to ensure that employees are not exposed to radiation. The government authority has approved the operation of the plant by legal requirements.

The elaborate physical protection measures include an additional 40-centimetre-thick concrete wall around the building and a protection door weighing around 45 tonnes.

Crash Tests

On 10 September 1959, the first crash test in the history of Mercedes-Benz took place – on open ground close to the plant in Sindelfingen. A test car was driven head-on into a solid obstacle. This opened a new chapter in safety research at Mercedes-Benz, as it made it possible to study the crash behaviour of both vehicles and occupants under realistic conditions using test cars and dummies. Together with the Group’s accident research analyses, crash tests form the basis for the “Real Life Safety” philosophy.

Mercedes-Benz conducts up to 900 crash tests annually and around 1,700 “sled tests” at Sindelfingen’s Vehicle Safety Technology Centre. In this crash simulation, a test sled is accelerated and braked.

A test object (vehicle body shell or assembly) is mounted on the sled and subjected to the forces arising during a real vehicle crash. These sled tests allow non-destructive testing of individual components, especially restraint systems such as seat belts.

The world’s first public crash test on two fully electric vehicles in autumn 2023 shows that safety at Mercedes-Benz is not a question of the drive system. EQA and EQS SUV models crash into each other in a real accident scenario at a speed of 56 km/h and an overlap of 50 per cent.

The test confirms the high level of occupant protection: Both vehicles’ passenger cells and high-voltage batteries remain intact as intended, the doors can be opened, and the high-voltage systems switch off automatically.