Effect of contact pressure on wear and friction of ultra-high molecular weight polyethylene in multidirectional sliding

Abstract

Please cite the original version: Saikko, Vesa. 2006 All material supplied via Aaltodoc is protected by copyright and other intellectual property rights, and duplication or sale of all or part of any of the repository collections is not permitted, except that material may be duplicated by you for your research use or educational purposes in electronic or print form. You must obtain permission for any other use. Electronic or print copies may not be offered, whether for sale or otherwise to anyone who is not an authorised user. ABSTRACTComputational wear models need input data from valid tribological tests. For the wear model of total hip prosthesis, the contact pressure dependence of wear and friction of ultra-high molecular weight polyethylene (UHMWPE) against polished CoCr in diluted calf serum lubricant was studied, and useful input data produced. Two test devices were designed and built, heavy load circularly translating pin-on-disk (HL-CTPOD) wear test device and HL-CTPOD friction measurement device. Both can be used with a wide range of loads. The wear surface diameter of the test pin was kept constant, 9 mm, whereas the load was varied so that the nominal contact pressure ranged from 0.1 MPa to 20 MPa. The wear factor decreased with increasing contact pressure, whereas the coefficient of friction first increased with increasing contact pressure with low pressure values, and then decreased. Up to the pressure of 2.0 MPa, the wear mechanisms and wear factors were in good agreement with clinical findings. In the critical range of 2.0-3.5 MPa, the wear mechanisms and wear factors started to differ from clinical ones, and the decrease of the wear factor steepened. The discrepancy became more and more evident as the pressure was gradually increased beyond 3.5 MPa. It appears that the pressure value of 2.0 MPa should not be exceeded in pin-on-disk wear tests that are to reproduce the clinical wear of UHMWPE acetabular cups.

Quantification of the effect of cross-shear on the wear of conventional and highly cross-linked UHMWPE

“…2 c). This is within the physiological range of contact pressure in human articular joints (Saikko, 2006). The pins were machined from ram-extruded non-cross-linked (0 MRad) and highly cross-linked (10 MRad) GUR 1050 UHMWPE.…”

“…Based on Hertizan theory (Johnson 1987), the real contact area shows a nonlinear increase with the increase in load, so, the wear factor would be decreased. In another study by Saikko (2006), it was suggested that the pressure value of 2 MPa should not be exceeded in the pin-on-disc wear tests, to achieve clinically comparable wear of UHMWPE cups. Therefore, further tests need to be carried out using a lower contact pressure, within this suggested limit, to reproduce higher wear factors under a range of CSs.…”

In vitro wear simulation on the RandomPOD wear testing system as a screening method for bearing materials intended for total knee arthroplasty

“…The wear factor of conventional UHMWPE is highly sensitive to the type of relative motion [Saikko et al, 2004;Saikko, 2014] and contact pressure [Saikko, 2006]. With decreasing multidirectionality and increasing contact pressure, the wear factor decreases significantly.…”

Modifying and Expanding the Simulation of Wear in the Spherical Joint With a Polymeric Component of the Total Hip Prosthesis

“…In [5], the polymer wear in terms of cumulative linear and volume wear when the wear factor is chosen to be a function of contact pressure was first evaluated. Herewith, various known wear factor dependencies on the contact pressure were investigated as contained in [9,10,11]. Since the contact pressure in the above formulae is a power function with a negative degree, these relations give a decrease in wear factor depending on the increase of a contact pressure, which means a reduction of wear values that are not uniquely consistent with the physics of the process.…”