Author: Khosro Fallahnezhad
Fallahnezhad, Khosro, 2018 An investigation on the fretting wear and corrosion damage to the head neck interface of total hip replacement: A finite element modelling approach, Flinders University, College of Science and Engineering
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Over the past years, modular design of hip joint replacement has attracted an increasing interest due to its several advantages. However, the modular design of hip joint implant can result in fretting wear in the interface of the head-neck junction, especially in metallic cases. As hip implant is operating inside the corrosive environment of human body, electrochemical corrosion occurs in metallic interfaces which is usually in the form of crevice corrosion. Combination of mechanical fretting wear and electrochemical corrosion results in fretting corrosion (mechanically assisted corrosion). Metallic debris and ions detached from the interface of the head-neck junction are proven to have detrimental influences on body tissues which can ultimately results in revision surgeries with its associated major risks.
This PhD project aims to comprehensively investigate fretting wear and corrosion failure of the head-neck junction of hip joint replacement, using a computational approach. In the first phase of this project, a three dimensional Finite Element (FE) model was developed and verified to investigate the mechanical environment of the head-neck junction. The model was then used to investigate the assembling process of the head neck junction and parameters that can influence the strength of the junction. This model was further developed to investigate the behaviour of the junction subjected to loading of daily activities. In this investigation several mechanical parameters that can influence on the fretting wear process were evaluated and a range of contact pressure (0-350 MPa) and micro-motion (0-32 µm) was suggested that can be used to develop more realistic in-vitro tests and FE simulations of fretting wear process. In the second phase of the project, an adaptive FE model was developed to simulate fretting wear process in the CoCr/CoCr head-neck junction. This model was developed for both dry and simulated body fluid conditions. It was revealed that simulation of fretting wear in a dry condition is a major simplification that cannot provide reliable outcomes. The model with the presence of the body fluid was then used to investigate the influence of angular mismatch (±0.124°) and assembly force (2-5 kN) on fretting wear process and the volume of material loss over several millions of fretting cycles. It was found that junctions with distal angular mismatch are more resistant against fretting wear. Moreover, results of this study revealed that although increasing the impaction force can enhance the strength of the junction, it can result in more damaging fretting wear process, in term of lost material. In the last phase of this project, for the first time, an adaptive FE model was developed to simulate fretting corrosion process. This model that was developed for a pin-on-disc geometry is able to quantify material loss caused by both fretting wear and electrochemical corrosion simultaneously it is also able to estimate the volume of the removed oxide layer, during the process of fretting corrosion.
The outcomes of this research provides a deep understanding about the performance of the head neck junction of modular hip replacement and different parameters that can play major roles in its failure. Moreover, the finite element model of fretting corrosion process that is presented in this thesis, can be a good platform to model this phenomena for different geometries and applications.
Keywords: Fretting corrosion; Fretting wear; Finite element; Material loss; Metallic interface
Subject: Engineering thesis
Thesis type: Doctor of Philosophy
Completed: 2018
School: College of Science and Engineering
Supervisor: Dr Reza Hashemi Oskouei