Unstructured tetrahedral elements for explicit large strain, dynamic impact on human body components

• Main Author: Marriott, H. M.
• Published: Swansea University 2001
• Subjects: 612
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.638006

Modelling the human body during impact with the use of the finite element method is of great interest and importance and is frequently used within the car and sport industry. The difficulties in using the finite element method for those situations described, lies in modelling the complex geometries of the human body successfully and being able to simulate the material properties of the human body. This thesis explores different numerical techniques that have been developed to model the human body more effectively. Structured hexahedral element are insufficient to model complex human geometries, hence tetrahedral elements have been concentrated on. In previous research a standard constant pressure tetrahedra and an average nodal pressure tetrahedra have been developed. This thesis explores new tetrahedral formulations, so as to overcome the inadequacies of the standard constant pressure and average nodal pressure tetrahedra. A split operator developed for solids, by Zienkiewicz et al based on a fluid mechanics algorithm which incorporates the time step splitting procedure originally proposed by Chorin is implemented. In addition a combined algorithm of the average nodal pressure and the split operator was proposed. The average nodal pressure was also noted to have poor behaviour when modelling bending dominated problems. The average deformation gradient tensor tetrahedra was developed and comparisons were made with the standard hexahedral element. Due to the average deformation gradient tensor tetrahedral element not exhibiting excessive stiffness the deformations under impact can create distorted elements and negative element volumes can occur, hence mesh quality enhancement was introduced. Finally several numerical examples are presented to demonstrate the applicability of the numerical techniques discussed within the thesis. The human body component used to demonstrate the theory is the lower leg.