The experts then used these values to determine the probability of certain injuries occurring to these body parts. “The crash tests with the dummy and numeric simulations with the human model both led to the same conclusion,” explains Boljen. Even at a seemingly low speed of only 10 km/h, a collision at a 90° angle results in enormous accelerations of 170 g on the human body.
Wearing a helmet and protective gear is therefore highly recommended, as these decrease the probability of serious injuries. “However, no helmet can prevent the accelerations acting on the head in the event of a direct impact; they can only reduce some components of these to a certain extent. Strictly speaking, the risk of traumatic brain injury exists whether the driver wears a helmet or not,” explains Boljen.
Need for research on helmets and protective gear
The researchers also discovered that the head impact speed measured in the simulation exceeds the maximum impact speed of 5.4 m/s stipulated in test standard DIN EN 1078 for bike helmet safety. In other words, conventional bike helmets and protective gear reduce the severity of the impact, but do not offer complete protection in collisions with hard objects. This is where the expertise of the researchers at Fraunhofer IWM comes into play. For more than 50 years, they have been analyzing materials and assessing their suitability for certain applications. For this purpose, they also use crash tests and perform other tests to determine mechanical effects on materials. In HUMAD, they investigated the suitability and protective effect of new materials.
Innovative protection concepts based on bionics
Dr. Jörg Lienhard, responsible for lightweight construction in the Component Safety and Lightweight Construction business unit, explains: “Protective gear often uses plastics with a honeycomb structure. Our tests in the laboratory showed that materials with a TPMS (triply periodic minimal surface) structure offered much better protection against kinetic effects.” The TPMS structure is characterized by repeating elements that form an “airy” open structure. This structure is particularly good at distributing kinetic energy from shocks across the surface area, therefore reducing the pressure on impact areas. The concept originates from bionics, taking inspiration from nature. For example, the chitin exoskeletons of insects have this type of structure.
TPMS helmets and protective gear could be 3D printed using all kinds of materials. According to Fraunhofer IWM expert Lienhard, besides the FDM (fused deposition modeling) process for thermoplastics and conventional stereolithography, the DLP (digital light processing) method is particularly well suited for large-scale production of plastic structures. It is similar to stereolithography in that the workpiece is built layer by layer. In contrast, however, DLP uses UV light generated by a projector, meaning that the entire layer can be cured at once. Several layers on top of each other give the material its desired form and structure. The material is cured using irradiation. At unexposed areas, the material simply drains off, leaving behind cavities that are characteristic of TPMS materials.
3D printing processes are very flexible and enable safety-related components or even vehicle parts to be individually produced for each application and its typical hazard profile — with DLP, this is now possible on a larger scale.
Conclusion of the HUMAD project: thanks to their small space requirement and flexibility, e-scooters offer an environmentally friendly solution for mobility in urban areas. However, it is important to treat them like you would a car — driving safely and responsibly. A helmet and protective gear should always be worn where possible. Looking to the future of urban mobility, Fraunhofer researchers are hopeful that protective equipment such as helmets and knee protectors as well as special light crash absorbers, which are specifically designed for certain vehicles and application scenarios, will be made available.
Fraunhofer experts are already planning the next phase of crash tests and simulations. These will also investigate the driver’s reflex movements during an accident and how these affect the risk of injury.