THE EFFECTS OF NECK STIFFNESS PROPERTIES ON BRAIN RESPONSE UNDER IMPACT LOADS

摘要

One primary concerns in computational modeling of brain under external loads is to defining the realistic boundary conditions and the head-neck junction stiffness. Neck is a complex structure with cervical spine, neck muscle and ligaments, when considered anatomically. The major mechanical function of the anatomical neck is to support the head through the cervical vertebrae. Few studies have focused on studying the response of head with neck and without neck. In this paper we examine the behavior of head under impact loadings with a simulated neck with elastic foundation- type stiffness. In this FE head -neck model, a three dimensional detailed head model is presented, while for neck, a simplified model of linear elastic springs is considered. The paramount interest is laid in modeling the mechanical functionality of the neck, rather than the modeling of the complete anatomical neck. Determining the exact stiffness properties for the springs, in order to (replicate) duplicate the neck functionality is the most complex aspect in this model. By considering the existing literature stiffness values of neck ligaments and cervical discs, four neck stiffness values ranging from zero stiffness to high stiffened neck have been chosen. A computational parametric examination of the varying the above considered neck stiffness properties are conducted to examine the impact of impact on the head model. Impact loading responses are examined against the Nahum's cadaver experiments. Numerical intracranial coup and contre-coup pressure histories during impact loading show good correlation with the respective experimental results. Brain intracranial pressure, maximum shear stress and strain response under impact are presented. A significant effect on the magnitude and pattern of brain shear stress and strains can be detected in comparison with the intracranial coup pressure response, with varying neck stiffness properties. Biomechanical multiscale studies on brain reveal that distortional strain is one of the main causes for the axonal injury, and this shear strain pattern significantly varies with neck stiffness properties.Thereby, it the extent of the role of the stiffness of the neck in predicting axonal injury can be examined.