Visualisation of body deformation during collision using X-rays

"The passive safety of a vehicle is controlled mainly by passenger restraint systems (seatbelt, airbag, etc.) and body crashworthiness. Currently, while simulation is fully utilized to design a whole vehicle and to predict its performance, conducting actual vehicle collision testing is still necessary to prove vehicle safety performance. Although passenger safety can be confirmed and evaluated dynamically during the collision through many sensors attached to dummies, it is challenging to observe vehicle performance in detail during a collision. Especially with respect to a body-in-white, in spite of its high contribution to the crashworthiness, little information can be obtained from currently existing measuring methods during a collision. Therefore, post-collision measurement is often used to validate crashworthiness performance, however it does not validate dynamic performance directly. This paper introduces an approach to observation of in-crash vehicle body deformation via X-ray. Due to its characteristics to pass through objects, X-ray enables interior observation during a collision. The target object for observation was toeboard deformation under IIHS Small Overlap Offset test, because this part strongly affects leg injuries, but cannot be seen directly during a collision using cameras. A static X-ray experiment was conducted first to optimisze the X-ray setup in order to provideensure maximal visibility of the toeboard. Lead markers were set at each measuring point on the toeboard to enable allocation of these points on the X-ray image. As it was very challenging to conduct the Small Overlap Offset test at the sled facility with a high-speed X-ray system, an alternative test condition, called “reverse Small Overlap Offset” was developed. According to physical laws, it was found that causing a moving barrier to collide with a static vehicle can demonstrate results similar to those of an actual Small Overlap test, if the barrier and the vehicle weights have been adjusted so that energy absorption by the vehicle matches between the two cases. Simulation was used to confirm the validity of the test configuration. Positioning of the X- ray source and detector, as well as design of a running barrier, were also conducted through simulation. The newly designed moving barrier was prototyped and the tests were conducted while only a few X-ray images could be taken due to the limitation of the energy source. Nevertheless, the deformation of the toeboard was able to be observed and measured quantitatively. Traditional post-crash measurement was also conducted to confirm the equivalence of the reverse crash mode to a Small Overlap test. The test result was compared with the simulation result to validate the precision of the simulation. Through the research and the actual test, it was proved that the dynamic observation of body deformation is possible using X-ray technology. With further enhancement of the technology, test results similar to those from the simulation may be observed. The results are also anticipated to contribute to the advancement of simulation technologies, and to the development of a new safety assessment, as they can provide more information on vehicle deformation during the collision process."