Structure, processing and performance of ultra-high molecular weight polyethylene (IUPAC Technical Report). Part 4: sporadic fatigue crack propagation

Bucknall, Clive; Altstädt, Volker; Auhl, Dietmar; Buckley, Paul; Dijkstra, Dirk; Galeski, Andrzej; Gögelein, Christoph; Handge, Ulrich A.; He, Jiasong; Liu, Chen-Yang; Michler, Goerg; Piorkowska, Ewa; Slouf, Miroslav; Vittorias, Iakovos; Wu, Jun Jie

Abstract

Fatigue tests were carried out on compression mouldings supplied by a leading polymer manufacturer. They were made from three batches of ultra-high molecular weight polyethylene (UHMWPE) with weight-average relative molar masses, ¯¯¯¯ M W, of about 0.6 × 106, 5 × 106 and 9 × 106. In 10 mm thick compact tension specimens, crack propagation was so erratic that it was impossible to follow standard procedure, where crack-tip stress intensity amplitude, ΔK, is raised incrementally, and the resulting crack propagation rate, da/dN, increases, following the Paris equation, where a is crack length and N is number of cycles. Instead, most of the tests were conducted at fixed high values of ΔK. Typically, da/dN then started at a high level, but decreased irregularly during the test. Micrographs of fracture surfaces showed that crack propagation was sporadic in these specimens. In one test, at ΔK = 2.3 MPa m0.5, there were crack-arrest marks at intervals Δa of about 2 μm, while the number of cycles between individual growth steps increased from 1 to more than 1000 and the fracture surface showed increasing evidence of plastic deformation. It is concluded that sporadic crack propagation was caused by energy-dissipating crazing, which was initiated close to the crack tip under plane strain conditions in mouldings that were not fully consolidated. By contrast, fatigue crack propagation in 4 mm thick specimens followed the Paris equation approximately. The results from all four reports on this project are reviewed, and the possibility of using fatigue testing as a quality assurance procedure for melt-processed UHMWPE is discussed.

Citation

Bucknall, C., Altstädt, V., Auhl, D., Buckley, P., Dijkstra, D., Galeski, A., Gögelein, C., Handge, U. A., He, J., Liu, C.-Y., Michler, G., Piorkowska, E., Slouf, M., Vittorias, I., & Wu, J. J. (2020). Structure, processing and performance of ultra-high molecular weight polyethylene (IUPAC Technical Report). Part 4: sporadic fatigue crack propagation. Pure and Applied Chemistry, 92(9), 1521-1536. https://doi.org/10.1515/pac-2019-0408

• Journal Article Type: Article
• Acceptance Date: Mar 20, 2020
• Online Publication Date: Aug 24, 2020
• Publication Date: 2020
• Deposit Date: Dec 9, 2020
• Publicly Available Date: Dec 9, 2020
• Journal: Pure and Applied Chemistry
• Print ISSN: 0033-4545
• Electronic ISSN: 1365-3075
• Publisher: International Union of Pure and Applied Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 92
• Issue: 9
• Pages: 1521-1536
• DOI: https://doi.org/10.1515/pac-2019-0408
• Public URL: https://durham-repository.worktribe.com/output/1255669