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A Novel Engineering Spherical Bearing, with Potential Application for a Hip Implant

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Journal of Mechanics Engineering and Automation 2016年第5期6卷 217-226页

作者： virgil florescu Lucian Capitanu Liliana-Laura Badita Viviana Filip The Mechanical Department Institute of Civil Engineering Bucharest 010153 Romania The Tribology Department Institute of Solid Mechanics of the Romanian Academy Bucharest 010141 Romania INCD-Mechatronics & Measurement Technique Bucharest 021631 Romania Institute of Multidisciplinary Research for Science and Technology Valahia University of Targoviste Targoviste 130004 Romania

It is a research which could enter into contradiction with the current trend concerning the hip implants. It is known as sliding friction, which is characteristic of present artificial hip joints, is higher than in the case of rolling friction. The paper reports the studies of the functioning mode of a novel spherical bearing MoM （metal on metal） with rolling friction, with potential application for an artificial hip joint obtained by introducing a number of balls between the femoral head and the acetabular cup. After over 15 years of research upon the functional principle and constructive solution, a version that offered a coefficient of minimum friction in the hip joint came to light. This version was based on a constructive solution of motion with lower friction, ＂Omnitrack~ movement solutions＂, which has been modified and rebuilt to be used as a joint of a total hip prosthesis--MOMJ. The joint was built entirely in stainless steel, SS316L medical grade. Tests have been carried out on the experimental laboratory devices that showed very low values of the coefficient of friction （μ = 0.0225）. For validation, the prosthesis had to be put through tests for 500,000 cycles, in terms of physiological motion and dynamic loading, according to ISO 14242-3. Testing was conducted on a multiaxial dynamics machine, MTS Bionix, equipped with system for hip implant testing. The testing results of this total hip prosthesis with rolling friction have been successful in signing up for a friction moment of 0.525 kNmm which means a coefficient of friction la = 0.0143, for a joint with femoral head diameter 28 mm.

关键词： Spherical joint total hip prosthesis rolling friction balls femoral head surface wear Omnitrack movement solutions laboratory testing.

Preliminary Study on the Seizure Trend of a MOM-THP with Self-directed Balls

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Journal of Mechanics Engineering and Automation 2013年第9期3卷 566-577页

作者： Lucian Capitanu Liliana-Laura Badita virgil florescu Dumitru-Catalin Bursuc Institute of Solid Mechanics of the Romanian Academy Bucharest 010141 Romania National Institute for Research and Development in Mechatronics and Measurement Technique Bucharest 043391 Romania Mechanical Department Institute of Civil Engineering Bucharest 050236 Romania Carol 1 National Defence University Bucharest 050662 Romania

This work continues the approach of one of our topics relating to a MOM-THP （metal on metal-total hip prostheses） with self-directed movement balls. Experiments revealed a certain seizure in some strain conditions. Laboratory trials for balls/plane Hertzian contacts have been restarted in order to determine seizure behaviour depending on the roughness of the flat area. 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.

关键词： MOM-THP with balls self-directed movement seizure optimal conditions wear scar friction coefficient.

Wear Aspects of Polymer Composites in Friction on Polished Steel Surfaces

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材料科学与工程（中英文A版） 2013年第6期3卷 382-397页

作者： Lucian Capitanu virgil florescu Tribology Department Institute of Solid Mechanics of the Romanian Academy Bucharest 010141 Romania Mechanical Departatment Institute of Civil Engineering Bucharest 050153 Romania

The introduction of various fillers provides an opportunity to improve the tribological behavior of polymers. Reinforcement with short glass fibers is used mostly to increase strength and therefore the bearing capacity of polymer composites. In case of glass fiber reinforced polymers in dry friction on polished steel surfaces, abrasive component gets a major role. In this work we studied on the Timken type couples (linear contact), the wear of steel surfaces duet the dry friction from polyamide with 30% glass fibers (Nylonplast AVE), polyamide with 20% glass fibers (NORYL) and polycarbonate with 20% glass fibers (LEXAN). It was recorded the influence of glass fibers content, normal load (implicitly the contact pressure), relative sliding speed and contact temperature over the metal surface wear and over the nature of wear mechanism. The volume of wear material was calculated based on Archard"s relationship (Vu = kNvt), by measuring the width of wear in three locations of trace, and depth and volume was calculated based on the "wear imprint method". To verify the results, an alternative and very accurate method was also employed, "the radiometric method", consisting in metal samples irradiation, collection of radioactive particles and measurement of the radioactivity of the entire wear quantity in comparison to a pattern of metal borings obtained while processing the metal sample. Investigations revealed that metal surface wear is dependent on all mentioned parameters, but to a large extent is also depended on the nature of materials in contact. Wear rates were determined as wear volume and depth.

关键词：高分子复合材料摩擦磨损钢表面抛光短切玻璃纤维放射性金属相对滑动速度金属表面

Studies Regarding Load Transfer Mechanism in MOM Total Hip Prostheses with Self-Directed Rolling Balls

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材料科学与工程（中英文A版） 2013年第5期3卷 355-362页

作者： Lucian Capitanu virgil florescu Liliana Laura Badita Tribology Department Institute of Solid Mechanics of the Romanian Academy Bucharest 010141 Romania Mechanical Departatment Institute of Civil Engineering Bucharest 050153 Romania Micro and Nanomechatronic Technolologies Laboratory National Institute for Research and Development in Mechatronics andMeasurement Technique Bucharest Romania

Starting with the well-known fact that the rolling movement always has a lower friction compared to sliding friction, the authors have conceived and realized a pivoting movement joint on a "layer of balls" with "compensation space", placed between the acetabular cup and the femoral head. This technical metal on metal (MOM) solution allows free self-directed migration of the balls, depending on the resistance opposed, with successive occupation of the "compensation space". As a concept, the proposed technical solution excludes the existence of a cage for maintaining the spheres relative positions. Changing the contact mechanism for the artificial hip joint from one sliding contact between two large surfaces, to a multitude of rolling contacts, could lead to serious problems regarding functionality and durability of the active prothesis elements. The key to an accurate evaluation of damaging mechanisms acting on total hip prosthesis (THP) with self directed rolling balls is a clear and complete picture of load transfer mechanism. The present paper summarize preliminary results regarding dynamics of some original design proposed by authors, combining general nonlinear finite element (FE) analyses of entire joint with analytical evaluations of local contacts.

关键词：荷载传递机理髋关节滚动球 MOM 导向假肢非线性有限元滑动摩擦