Date of Award

2012

Degree Type

Thesis

Degree Name

Master of Engineering Science

School

School of Engineering

Faculty

Faculty of Computing, Health and Science

First Advisor

Dr. Zonghan Xie

Second Advisor

Dr. Xiaoli Zhao

Abstract

Demand for joint replacements is rising in Australia, driven by a sharp increase in the number of joint problems associated with population aging and obesity. In artificial joints, delamination or failure within the coatings occurs when the stress reaches a critical level, resulting in large wear debris particles appearing on the contact surface between the head and the cup. The process has been described as due to a stress-corrosion-cracking mechanism. Under the same loading, stress increases when the contact area decreases, which happens in the vicinity of wear debris. As such, once wear debris is generated, a catastrophic process could be initiated, resulting in more stress-corrosion-cracking. As such, acquiring a strong coating that will not fail is highly desirable for the applications of hip joint replacement. Failure in a coating layer is normally initiated by excessive local tensile or shear stress; therefore, it is important to clarify the stress distribution within the coating layer under different loading conditions, which is necessary for improving the load-carrying capability of the coating. Unlike previous studies, the multilayer diamond-like carbon (DLC) coatings having high elastic modulus and hardness were analysed in this work. Under normal contact conditions, plastic deformation occurs in contacting materials when the contact pressure is greater than the hardness of the materials. Therefore, high hardness coatings can resist plastic deformation to avoid failure of the coating; in addition, multilayer coatings can decrease stress concentration to avoid cracking. The purpose of this study is to determine whether DLC multilayer coatings can improve the property of the coating against potential cracking in the coating. It has been shown that structurally graded coatings had effect on reducing the contact-induced stress among all the factors considered. It is anticipated that the multilayer design parameters will be important to understand the stress distribution within metal-on-metal (MOM) hip replacements.

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