Safety Crash test under X-rays

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Mercedes and Fraunhofer EMI have monitored a crash test with X-rays. The developers expect this to provide more precise insights into deformations during an impact.

Mercedes-Benz, in collaboration with the Fraunhofer Institute for High-Speed Dynamics, Ernst Mach Institute (EMI), conducted what the company claims to be the world's first X-ray crash test with a real car. On board, on the impact-facing left side, were two dummies of the model "SID IIs". These are test bodies with female anatomy, specially designed for side impact tests.

The special feature of this test: A linear accelerator mounted above the vehicle served as the X-ray source. According to Mercedes, short-time X-ray technology allows for the representation of highly dynamic internal deformations. Deformations that were previously invisible and their exact processes are thus traceable. Numerous high-resolution images allow for a precise analysis, according to Mercedes.

How does the X-ray crash work?

During the crash test, the rays penetrate the body of the car and any dummies from above. An X-ray detector is located under the test vehicle. It serves as an image receiver: when the radiation hits the detector, an electrical signal is generated.

The intensity of the generated signal depends on how much the radiation was absorbed by the vehicle and dummy structure before. This influences the gray value visible later – similar to the X-ray inspection of luggage at the airport or corresponding medical images.

Specifically: During the actual impact time of one-tenth of a second, the X-ray system creates about 100 still images. "Combined into a video, they provide highly exciting insights into what happens inside safety-relevant components and the body of the dummy during the crash," Mercedes states. "This allows for detailed observation of how the dummy's thorax is compressed or a component deforms."

It's important to note: The X-ray crash does not affect any other analysis tools. For example, the interior cameras of the crash test vehicle continue to record undisturbed.

Radiation protection concept for the crash

For the X-ray crash, the developers at EMI have created a radiation protection concept. They use dosimeters to ensure that employees are not exposed to radiation. The government agency has approved the operation of the facility according to legal requirements.

Physical protection measures include an additional concrete wall, 40 centimeters thick, around the building and a radiation protection door weighing about 45 tons.

Up to 1,000 images per second

For several years, Mercedes-Benz and EMI have been researching the use of X-ray technology in crash testing. According to the announcement, the key to the current breakthrough was using a linear accelerator with 1-kHz technology as the radiation source.

The device is far more powerful than the X-ray flashes previously used on a trial basis: The photon energy of the linear accelerator amounts to up to nine mega-electron volts. "This allows us to X-ray all the materials commonly used in vehicle construction," Mercedes announces. The duration of the X-ray pulse is only a few microseconds.

This allows deformation processes in the crash test to be recorded without motion blur. Moreover, the linear accelerator generates a continuous stream of these X-ray pulses. Up to 1,000 images per second are thus possible.

About the Fraunhofer Institute for High-Speed Dynamics, Ernst Mach Institute (EMI)

The Fraunhofer EMI deals with the physics, engineering, and computer science of rapidly occurring processes in experiment and simulation. The goal is to develop concepts for industrial applications with a focus on reliability, safety, resilience, efficiency, and sustainability.

The institute deals with crash, impact, and shock wave phenomena across materials. The EMI analyzes and optimizes a range of materials, microstructures, and complex structures. Applications include materials, components, automobiles, aircraft, satellites, buildings, urban systems, or infrastructure networks.