Modelling of occupant biomechanics with emphasis on the analysis of lower extremity injuries

Abstract

This paper addresses the use of finite element method to the simulation of humans in an impact environment. An extensive literature survey reveals several rigid body dynamics models of the human and sub-components, however, relatively little work has been performed using finite elements. Difficulties remain in characterising the material properties of the associated biological materials because of non-linear, inhomogeneous, anisotropic, and rate dependent behaviour. Physical testing using cadavers remains the primary means for determining human impact response and for validating the models created. A method for creating human finite element models is presented which requires the model to be developed in a ground-up approach and in a componentwise manner. Each component has five levels of detail with level one being a collection of rigid segments connected by simple joints and level five consisting of a highly detailed model with proper material properties and injury mechanisms included. This method has been employed to create a level two human lower extremity model. The model consists of accurate geometric segments of the individual bones in the leg. Each segment is connected using joint definitions in LS-DYNA3D that contain the non-linear stiffness characteristics of the hip, knee, and ankle. The model was used to simulate the loading conditions of a 50% overlap frontal collision of two mid-sized cars with a closing speed of 112 km/hr (70 mph). A parametric study to determine the effects of muscle tensioning was performed for twenty-seven different joint loading cases. Results indicated that muscle tensioning greatly affected the kinematics of the leg during high speed impact events. Greater stiffness in the hip and knee directly resulted in a higher potential for injury in the ankle. In addition, higher levels of muscle activation in the ankle reduced injuries from the deceleration pulse of the impact, however, toepan intrusion still presented potential harm to the ankle. Language: en