Abstract
In biomechanical finite element (FE) simulations, the mechanical nonlinear behaviors must be considered frequently and depend on several properties, such as structural, material, and contact situation. The hexahedral meshes were widely applied to the modeling with the mechanical nonlinearities and can decrease the computer resources and improve the accuracy of the simulations. However, it is quite difficult to construct the three-dimensional hexahedral meshes of complicated shapes such as human joints.
This study proposes the development of the semi-automatic meshing technique which consists of only hexahedral elements, thereby reducing the number of elements without spoiling the shape fidelities. In order to create the three-dimensional models of the tibial plateau and femoral condyle, the simply-shaped ‘seed’ models consisting of only hexahedral elements were prepared. The seed meshes were located into the surface of the target bone and expanded until they fitted the target surface. When the seed meshes expanded and intersected with the target surface, the contact condition was detected and the seed surface slide on the target one. These procedures are repeated until the seed meshes filled up inside the complicated target surface. Figure 1 shows the transformed and filled seed meshes inside the surface. The boundary between the cortical and cancellous bone was kept clearly. In the finite element meshes, there was no concentration of elements, and each hexahedral element had the good aspect ratio.
Figure 2 shows the impact FE simulation of the TKR joint model, which was constructed by hexahedral elements using this technique. The impact stress propagated cleary through the TKR joint. The number of elements were reduced by a sixth, compared with that of the tetrahedral ones. Because the number of nodes and elements of the model can be defined beforehand, it is easy to predict the scale of the final model. Therefore, this technique is very effective in creating the huge skeltal models which build the complicated biomaterial shapes by the hexahedral elements.
