Wyniki wyszukiwania - BazTech

Ograniczanie wyników

Znaleziono wyników: 2

Liczba wyników na stronie

Wyniki wyszukiwania

Wyszukiwano:
w słowach kluczowych: metal-on-metal

Sortuj według:

Ogranicz wyniki do:

Comparison of wear processes of biomaterials used in hip joint implants

Ortega-Saenz J. A., Kalbarczyk M., Michalczewski R., Piekoszewski W., Szczerek M.

Scientific Problems of Machines Operation and Maintenance

2008

Vol. 43, nr 4

15-26

In the last century, two different prosthetic systems for total hip joint replacement were introduced at the same time: metal-on-metal (MOM) and metal-on-UHMWPE (MOP). The tribosystem MOP was successful, because the MOM bearing system showed unsatisfactory short-term performance and practically disappeared. But nowadays, the idea of an all-metal joint was taken up again and led to the development of the second generation of metal articulation with improved alloy microstructure, surface finish, and manufacturing tolerances. The current work presents a tribological study of the metal-on-metal and metal-on-UHMWPE bearing couples by means of a reciprocating pin-on-flat testing machine. In this study, it was found that the wear intensity and coefficient of friction are at least three times higher in the MOM friction pair than in MOP bearing system. The wear mechanisms observed for the MOM friction pair are abrasion, surface fatigue, and adhesion. For the MOP friction pair, the soft polymer smearing process on the hard metal surface was observed.

Lata 60. ubiegłego stulecia to początek alloplastyki stawów biodrowych. Skojarzenia materiałowe wówczas stosowane do produkcji sztucznych stawów to głównie pary: metal-metal (MOM) i metal-polimer (MOP). Wkrótce para metal-metal została wyparta ze względu na znacznie gorsze właściwości tribologiczne. Obecnie idea stosowania skojarzeń metalowo-metalowych powraca, między innymi z powodu postępu w kształtowaniu mikrostruktury materiałów, technik przygotowania i wykończenia elementów endoprotez. Praca przedstawia wyniki wstępnych modelowych badań tribologicznych materiałów na endoprotezy w ruchu oscylacyjnym, za pomocą urządzenia typu trzpień-płytka. Badaniom poddano skojarzenia metal-metal i metal-UHMWPE (polietylen wielkocząsteczkowy). Zaobserwowano, że intensywność zużywania oraz współczynnik tarcia jest przynajmniej trzy razy wyższy dla skojarzenia metal-metal niż dla skojarzenia metal-UHMWPE. W przypadku pary metal-metal zachodzi zużywanie ścierne, zmęczeniowe i adhezyjne. W przypadku pary metal-polimer zachodzi proces przenoszenia miękkiego polimeru z trzpienia na twardą powierzchnię metalu.

Lubrication analysis of metal-on-metal hip joint prostheses in a free pendulum machine

Udofia I. J., Jin Z. M.

International Journal of Applied Mechanics and Engineering

2002

Vol. 7, no 3

1015-1024

Total joint arthroplasty is probably the most effective treatment for severe degenerative bone diseases such as osteo-arthritis. There has been renewed interest in the use of hard bearings, particularly the metal-on-metal combination for hip joint replacements due to the osteolysis problem associated with current metal-on-polyethylene prostheses. The potential for full fluid film lubrication has been shown to exist during part of the walking cycle in these hard bearing joints. In this study, theoretical and numerical analyses were carried out to characterise the loading and velocity and the corresponding lubrication regime in a typical metal-on-metal hip joint replacement tested in a free pendulum machine. It was shown that the loading in the joint remains relatively constant throughout the duration of swing. The maximum angular velocity achieved under frictionless conditions with an initial angular displacement of 5o, was found to be about 0.387 rad/s, corresponding to a sliding velocity of 5.412 mm/s for a femoral head radius of 14mm. The lubricating film thickness due to the entraining action is only 0.011 micro m, which implies at best a mixed lubrication regime is experienced for the metal-on-metal hip joint tested in a pendulum machine with an average surface roughness of about 0.01 micro m. Under squeeze-film motion, the lubricating film thickness decreases to only about 0.01 micro m after the first few swings, assuming an initial separation between the head and the cup by the radial clearance. The theoretical predictions are consistent with experimental observations reported in literature. The lubrication regime under more realistic walking conditions cannot be deduced in the pendulum machine, largely due to the inappropriate loading and velocity conditions experienced in the pendulum.