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Research Papers: Friction and Wear

Effect of CoCr Counterface Roughness on the Wear of UHMWPE in the Noncyclic RandomPOD Simulation

[+] Author and Article Information
Vesa Saikko

Department of Engineering Design and Production,
School of Engineering,
Aalto University,
PO Box 14300,
Aalto FI-00076, Finland
e-mail: vesa.saikko@aalto.fi

Vesa Vuorinen

Department of Electronics,
School of Electrical Engineering,
Aalto University,
Aalto FI-00076, Finland

Hannu Revitzer

Department of Chemistry,
School of Chemical Technology,
Aalto University,
Aalto FI-00076, Finland

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received January 7, 2016; final manuscript received May 10, 2016; published online August 11, 2016. Assoc. Editor: Zhong Min Jin.

J. Tribol 139(2), 021606 (Aug 11, 2016) (6 pages) Paper No: TRIB-16-1008; doi: 10.1115/1.4033648 History: Received January 07, 2016; Revised May 10, 2016

With the random motion and load pin-on-disk (RandomPOD) wear test system, conventional and highly crosslinked ultrahigh molecular weight polyethylenes (UHMWPE) were run against CoCr counterfaces with different surface roughnesses. The unique 16-station, computer-controlled pin-on-disk device produced noncyclic motion and load. With appropriate specimen shapes, simulations of wear mechanisms of both hip and knee prostheses were performed. Against polished counterfaces, the crosslinked UHMWPE showed negligible wear. Its wear against severely roughened counterfaces was close to that of conventional UHMWPE against polished counterfaces. The reduction in wear with crosslinked versus conventional UHMWPE was 80–86% in the hip and 87–96% in the knee wear simulation. The wear particles were of clinically relevant size and shape which indicated realistic wear mechanisms.

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Figures

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Fig. 2

Optical micrographs from the center of spherical (radius = 28 mm) bearing surfaces of CoCr pins for abrasive knee wear tests. Pins have been roughened so that their mean Sa values are (a) 0.21 μm, (b) 0.30 μm, (c) 0.42 μm, and (d) 0.67 μm.

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Fig. 3

White light interferometry scan of the roughest disk with surface roughness Sa = 0.92 μm, Sp = 4.4 μm, Ssk = −1.1, and Sk = 2.6 μm

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Fig. 6

Scanning electron micrographs of UHMWPE wear particles: (a) crosslinked UHMWPE, hip wear simulation, counterface surface roughness Sa = 0.07 μm, (b) conventional, hip, Sa = 0.07 μm, (c) crosslinked, hip, Sa = 0.89 μm, (d) conventional, hip, Sa = 0.89 μm, (e) crosslinked, knee, Sa = 0.21 μm, (f) conventional, knee, Sa = 0.21 μm, (g) crosslinked, knee, Sa = 0.67 μm, and (h) conventional, knee, Sa = 0.67 μm

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Fig. 5

Optical micrograph from conventional UHMWPE disk worn against spherical CoCr pin with surface roughness Sa value of 0.21 μm in knee wear simulation. Lumps of rolled wear debris show no orientation due to noncyclic relative motion.

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Fig. 4

Variation of UHMWPE wear factor k with counterface surface roughness Sa and best-fit equations. Open symbols represent conventional UHMWPE, and filled symbols crosslinked UHMWPE. Circles represent hip wear simulation, and diamonds knee wear simulation.

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Fig. 1

Schematic of the pin-on-disk test configurations: (left) flat-on-flat hip wear simulation and (right) ball-on-flat knee wear simulation

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