Vehicle occupants instinctively prepare for an accident in order to protect themselves: They tense their muscles, support themselves on the steering wheel or push the brake pedal through. This behaviour influences the outcome of the accident. Conventional crash test dummies do not have the ability to react; they do not map human behaviour before a crash. In the automotive sector, digital computer models are therefore increasingly being used in FE simulations (finite element simulations) to reproduce the movements of the occupants shortly before the accident and thus improve the safety of automobiles. "The musculature has a major influence on how a vehicle occupant reacts shortly before an accident and how the body behaves during the crash. This can lead to serious deviations from stiff and kinematically restricted crash test dummies," says Dr. Matthias Boljen, a scientist at the Fraunhofer EMI.
Bolien's team uses human models in finite element simulations, focusing on muscle stiffness in the latest tests to assess occupant safety. The researchers investigated the effects of changes in muscle stiffness on the kinematics of the occupants, breaking new scientific ground. So far, only the generation of movement by contractile muscles has been realized in human models, but not the muscle stiffness associated with contraction. "If a driver rests on the steering wheel before the collision, not only does the muscle shorten, but the muscle becomes stiffer as a result of the contraction. Previous FE simulations of individual muscles and muscle groups of entire human models did not take contraction into account," explains the researcher.
This gap was addressed by Niclas Trube, a colleague of Boljen's, who used the THUMS Version 5 human model for his investigations. He defined four different stiffness states and tested the influence of these changes on a simulated frontal crash. The result: the muscle stiffness has a decisive influence on the behaviour of the vehicle occupants. Depending on the degree of stiffness, different injuries can be expected in an accident.
"This finding could be of great importance for the further development of human models, especially with regard to autonomous driving. Vehicle interiors will be redesigned in the future, so existing concepts for seat belts and airbags will also have to be reconsidered. Human models are a valuable tool here," says Trube.