[Capitanu, 3(7): July, 2014] ISSN: 2277-9655 Scientific Journal Impact Factor: 3.449 (ISRA), Impact Factor: 1.852 http: // www.ijesrt.com (C)International Journal of Engineering Sciences & Research Technology [319-328] IJESRT INTERNATIONAL JOURNAL OF ENGINEERING SCIENCES & RESEARCH TECHNOLOGY Study on the Seizure Trends, Friction and Lubrication in a Total Hip Prosthesis with Self- Directed Balls L. Capitanu *1 , V. Florescu 2 , C. Tiganesteanu 1 , D.C. Bursuc 3 *1 Professor, Tribology Department, Institute of Solid Mechanics, 010141 - Bucharest, Romania 2 Professor, Department of Mechanical Engineering,Institute orf Civil Engineering, Bucharest, Romania 3 Carol I Defence University, Bucharest, Romania lucian.capitanu@yahoo.com Abstract Although Metal-On-Metal (MOM) Total Hip Prostheses (THP) with self directed balls have as their greatest advantage the replacement of the specific regular hip prostheses sliding movement between the femoral head and the acetabulum socket with the rolling movement between the balls, the socket and the femoral head, the lubrication side of the process is still not well known. Laboratory trials on the ball on the flat rig showed maximum values of the coefficient of friction under 0.05, and studies of lubrication with saline solution have indicated a lubrication schedule EHL, the minimum value for the thickness of the lubrication film (hmin), measured through the contact resistance methodology, being 0.06 μm, in the operation of these prostheses are obvious trends of seizure. The trials have been carried out in BSF (body simulated fluid) lubrication conditions, much closer to the real operating conditions up against the initial tests with distilled water. Seizure burdens to different loadings and contact surfaces roughness influence over the seizure burden have been determined. Even though the minimum value of the wear must be the same with the minimum value of the surfaces roughness, given the experimental conditions, it came out from the trials results on wear that the lowest level of wear is acquired at a certain value of roughness, not at the lowest level of roughness. There are obvious trends of seizure in the operation of these prostheses. However, preliminary studies on lubrication in MOM - THP also showed a clear seizure tendency. For the purposes of the present study we opted for changing the constructive version, adopting a modified motion Omnitrack solution, adapted for use in an artificial hip joint. After testing on an experimental device, the results were spectacular. The minimum friction coefficient value is 0.007, while the maximum value reaches 0.02. Keywords: MOM THP, self directed balls, friction coefficient, friction evolution, lubrication Introduction All content Nowadays, the design solutions for THP (total hip prostheses) are diverse encompassing for improving the materials used for prostheses elements and reshaping geometrically and/or tribologically the load transfer path. In such context THP with rolling balls have been found as a possible viable alternative design to current industrial products, based on low friction of rolling contact, against sliding one (now used in most industrial designs). Different designs of THP with rolling bodies have been developed in order to improve the tribological performances of the artificial joint. We could mention here the design with ball train, proposed by Katsutoshi and Kiyoshi [1], the French “Supertête prostheses” [2], or the design with conical rolling elements proposed by Imperial College of Science, Technology and Medicine of London [3]. The French design, obtained by “The foundation for the future” in collaboration with The Ministry of Defance, Mission of Innovation, proposes the insertion of a frictional contact inside a bearing. The design suggested by Imperial College of Science, Technology and Medicine of London consists in a major modification of elements between the femoral part stem neck and the modular hip prosthesis by introducing a rolling bearing with conical femoral artificial head. The bearing rotation axis corresponds with the axis of femoral stem neck, the rolling elements being guided by both the external surface of stem neck and the internal surface of the ball replacing the femoral head. But changing the contact mechanism from sliding to rolling in a hip prosthesis is not an easy task due to difficulties encountered in establishing the load transfer path, a critical