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RESEARCH PAPERS

Stress Intensity Factors for a Vertical Surface Crack in Polyethylene Subject to Rolling and Sliding Contact

[+] Author and Article Information
A. W. Eberhardt, B. S. Kim

Department of Materials and Mechanical Engineering, University of Alabama at Birmingham, Birmingham, AL 35294-4461

J Biomech Eng 120(6), 778-783 (Dec 01, 1998) (6 pages) doi:10.1115/1.2834893 History: Received March 10, 1998; Revised July 22, 1998; Online January 23, 2008

Abstract

Pitting wear is a dominant form of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In the present study, stress intensity factors, KI , and KII , were calculated for a surface crack in a polyethylene-CoCr-bone system in the presence of rolling or sliding contact pressures. Variations in crack length and load location were studied to determine probable crack propagation mechanisms and modes. The crack tip experienced a wide range of mixed-mode conditions that varied as a function of crack length, load location, and sliding friction. Positive KI values were observed for shorter cracks in rolling contact and for all crack lengths when the sliding load moved away from the crack. KII was greatest when the load was directly adjacent to the crack (g/a = ±1), where coincidental Mode I stresses were predominantly compressive. Sliding friction substantially increased both KI max and KII max . The effective Mode I stress intensity factors, Keff , were greatest at g/a = ±1, illustrating the significance of high shear stresses generated by loads adjacent to surface cracks. Keff trends suggest mechanisms for surface pitting by which surface cracks propagate along their original plane under repeated reciprocating rolling or sliding, and turn in the direction of sliding under unidirectional sliding contact.

Copyright © 1998 by The American Society of Mechanical Engineers
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