Wear debris from ultra-high molecular weight polyethylene (UHMWPE) components used for joint replacement prostheses can cause significant clinical complications, and it is essential to be able to predict implant wear accurately in vitro to prevent unsafe implant designs continuing to clinical trials. The established method to predict wear is simulator testing, but the significant equipment costs, experiment time and equipment availability can be prohibitive. It is possible to predict implant wear using finite element methods, though those reported in the literature simplify the material behaviour of polyethylene and typically use linear or elasto–plastic material models. Such models cannot represent the creep or viscoelastic material behaviour and may introduce significant error. However, the magnitude of this error and importance of this simplification has never been determined. This study compares the volume of predicted wear from a standard elasto–plastic model, to a fractional viscoelastic material model. Both models have been fitted to experimental data. Standard tensile tests in accordance with ISO 527-3 and tensile creep-recovery tests were performed to experimentally characterise both (a) the elasto–plastic parameters and (b) creep and relaxation behaviour of the ultra-high molecular weight polyethylene. Digital image correlation technique was used in order to measure the strain field. The predicted wear with the two material models was compared for a finite element model of a mobile-bearing unicompartmental knee replacement, and wear predictions were made using Archard’s law. The fractional viscoelastic material model predicted almost ten times as much wear compared to the elasto-plastic material representation. This work quantifies, for the first time, the error in troduced by use of a simplified material model in polyethylene wear predictions, and shows the importance of representing the viscoelastic behaviour of polyethylene for wear predictions.
Alotta, GioacchinoBarrera, Olga Pegg, Elise C.
Faculty of Technology, Design and Environment\School of Engineering, Computing and Mathematics
Year of publication: 2018Date of RADAR deposit: 2018-04-27