MECHANISTIC STUDY OF CRACK INITIATION AND PROPAGATION IN CROSSLINKED ULTRA HIGH MOLECULAR WEIGHT POLYETHYLENES (UHMWPE) SUBJECTED TO STATIC AND CYCLIC LOADING

Many total joint replacement (TJR) designs incorporate a hard bearing material articulating against a soft bearing (polymeric) material. The bearing polymer, typically made of ultra high molecular weight polyethylene (UHMWPE) has been successfully used for the last four decades. However, these bearing materials can fail as a result of in vivo mechanical loads. Reports suggest that the fracture resistance of UHMWPE could be improved which can help the longevity of the components in vivo. Fatigue crack propagation behavior of two crosslinked UHMWPE formulations was investigated to estimate the mechanical governing factor for stable crack propagation. Frequency, waveform and R-ratio were varied between test conditions to determine the governing factor for fatigue crack propagation. It was found that the crack propagation velocity in crosslinked UHMWPE is driven by peak stress intensity (Kmax) in a loading cycle. The findings suggest that stable crack propagation can occur in a static mode rather than in a cyclic mode. Crack initiation from a notch under fatigue conditions is also investigated for remelted 100 kGy material and compared to crack initiation under constant loading conditions. Crack initiation times for fatigue loading conditions were found to be substantially lower compared to static loading conditions. The results suggest that the crosslinked UHMWPE material is resistant under static loading conditions compared to fatigue loading conditions.Fracture resistance of two crosslinked UHMWPE formulations was also investigated. Fracture research utilizing the traditional LEFM and EPFM approaches has not yielded a definite failure criterion for UHMWPE. Therefore, an advanced viscous fracture model has been applied to various notched compact tension specimen geometries to estimate the fracture resistance. Results suggest that the viscous fracture model can be applied to the crosslinked UHMWPE materials and a single value of critical energy (Jc) governs crack initiation and propagation in these materials. This is the first report of a mechanistic approach to crack initiation and propagation in UHMWPE for a range of clinically relevant stress-concentration geometries. A combination of structural analysis of components and material parameter quantification is a path to effective failure prediction in total joint replacement bearings.

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

EMC - Mechanical Engineering

Grantor dc:publisher

Case Western Reserve University School of Graduate Studies

Year dc:date

2013

Author dc:creator

• Sirimamilla, Pavana Abhiram

Contributors dc:contributor

• Rimnac, Clare

• Engineering
• fatigue crack propagation
• fatigue crack initiation
• crosslinked UHMWPE
• viscous fracture model
• initiation time

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=case1345862222

OAI identifier oai:identifier

oai:etd.ohiolink.edu:case1345862222