Oguz Kayabasi

Finite element modelling and analysis of a new cemented hip prosthesis

In this study, four different stem shapes for hip prosthesis have been designed to investigate an optimum stem shape. The stem shapes have geometries of varying curvatures. The first stem has standard straight geometry. The other two have notched geometries and the last one has curved geometry. The notched and curved types have been intended to reduce sliding of the implant in the bone-cement. They have been also aimed the implant to stick to the bone-cement securely. The static and dynamic FE analyses of the stems have been conducted using implicit commercial finite element code. The static analyses have been conducted using a load of an average body weight. The dynamic analyses are performed using a load of walking condition of a human. Based on static and dynamic FE analysis results, safety factors for fatigue life of the hip prosthesis have been calculated. Fatigue calculations have been carried out for Ti-6A1-4V, cobalt-chromium alloy materials and bone cement based on Goodman, Soderberg, and Gerber fatigue theories. All calculations have been performed according to the infinite fatigue life criteria. The results obtained have been compared and concluded to the results found by Charnley.

3-D Rail-Wheel contact analysis using FEA

Mechanics of the Rail-Wheel contact is one of the fundamental areas of the study in Railway Engineering, requiring both vast application expertise and dependable analysis approaches. Analytical formulations describing the physics of this phenomenon are only defined for certain type of simple contact geometries, therefore for more complicated geometries the analytical models utilizing closed formulations remain elusive. Remaining option is to utilize numerical computation methods. Railway engineers are, to the certain extent, successfully applied one of the numerical computation techniques known as Finite Element Analysis (FEA) into Rail-Wheel contact problems to validate their results by comparing them to their real life data obtained over the years. In the literature, most of the work on the Rail-Wheel contact FEA is either 2-dimensional axi-symmetric or simple 3D Rail-Wheel models with poor mesh count/quality or undesired Tet-mesh, latter known to exhibit stiff deformation characteristics during the deformation. Also, in majority of the FEA studies, boundary conditions and/or total load are applied with some approximations. This study focuses more on the fundamental way of handling Rail-Wheel contact problems from the FEA standpoint, and highlights required steps for more realistic 3D solutions to these types of problems. 3D FE analysis results obtained show good agreement with real life problems experienced at both railway Wheel and Rail.