The term 'whiplash' was initially used to describe injuries to the neck caused by the head being forced backwards during a rear-end collision in cars without head restraints. The addition of head restraints in the 1970s was expected to solve this problem by preventing excessive extension of the neck but experience suggests the problem still exists. This paper reviews available experimental studies of whiplash and uses the data to construct a finite element model which is capable of dynamically simulating whiplash collisions and predicting the forces in all the relevant neck ligaments. For the first time, it is shown that trauma occurs long before the head hits the head restraint as a result of displacement between the head and the torso caused by the head's inertia leading to markedly different acceleration histories. It is concluded that experimental and computational studies must be used together to produce progress in biomechanical studies.
A biomechanical finite element (FE) model of the 50th percentile male human cervical spine, capable of predicting ligament loadings in whiplash scenarios, has been developed and previously reported. The study reported here analyses the influence of seat back rake on ligament injury in two scenarios: firstly, the in position, where the car occupant is looking forward and the head remains in the sagittal plane, and, secondly, the out of position, where the car occupant is initially looking slightly to one side. In both cases the results show an increase in ligament loading with a decrease of seat back rotational stiffness, substantiating the need for dynamic seat testing. Moreover, comparing individual ligament loading data shows that the initial head rotation scenario is more damaging to the cervical spine than the sagittal plane scenario, confirming a published hypothesis.
Significant progress in car occupant safety has been made through the use of safety devices such as airbags and seat belts, as well as in the construction of the car body itself. Much still needs to be done, however, in order to satisfy increasingly stringent legislation and public demand. This work deals with the problem of whiplash injuries which so far, due to difficulties in diagnosis, have been very difficult to investigate let alone prevent. A new advanced biomechanical FE model of the head-neck complex has been created and combined with the Hybrid 111 FE dummy model, which is an industry standard for occupant safety. The final model has been used to study whiplash accidents for a representative range of car seats. The simulation clearly shows the effects of seat back stiffness and head restraint position. It also illustrates the unique contribution that is possible for combined biomechanicaVdummy modelling in vehicle safety design, considering a simple whiplash protection device.
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