Numerous studies have shown head injuries to be the leading cause of death and severe disability in both cyclists and pedestrians. Current bicycle helmets are able to reduce approximately 60% of severe head injuries in cyclists. This stresses the high potential of bicycle helmets to further reduce cycling-related severe injuries and fatalities. This dissertation handles biomechanical aspects of cyclist head impact injuries and the improvement of current bicycle helmets. A first research topic is the mechanical origin of human skull fractures, both on macro- and microscopic scale. On the macroscopic scale, skull and head impact tests are used to study the biomechanical impact tolerance of the head. On the microscopic scale, three point bending tests are performed to quantify the intrinsic, viscoelastic material properties of human cranial bone. A second field of study evaluates both current and new head lesion criteria for skull fracture, acute subdural haematoma, diffuse axonal injury and brain contusion. This leads to better insight into severe skull and brain injuries, and to recommendations towards current head injury criteria and helmet standards. For this research topic, analyses of cyclist falls and cyclist-car collisions are performed using multibody modelling software. Combining the skull characterisation tests and the multibody analysis results, leads to a third research topic, namely the influence of the human body on the kinematics of the human head, and resulting skull and brain lesions. A final topic of research is from a more practical nature, linking directly to the general aim of the K.U. Leuven bicycle helmet group to improve modern bicycle helmets. This goal is to evaluate new materials to be used in a new bicycle helmet concept and to provide practical recommendations for a new and optimised helmet design. A large focus within this goal is on the reduction of rotational acceleration of the head, which can be directly linked to relative brain-skull motion, which in its turn correlates to brain injury. (Author/publisher)
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