In:
Pure and Applied Chemistry, Walter de Gruyter GmbH, Vol. 92, No. 9 ( 2020-09-25), p. 1521-1536
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 ${\overline{M}}_{\mathrm{W}}$ , of about 0.6 × 10 6 , 5 × 10 6 and 9 × 10 6 . 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, Δ K , is raised incrementally, and the resulting crack propagation rate, d a /d N , 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 Δ K . Typically, d a /d N 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 Δ K = 2.3 MPa m 0.5 , there were crack-arrest marks at intervals Δ a o f 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.
Type of Medium:
Online Resource
ISSN:
1365-3075
,
0033-4545
DOI:
10.1515/pac-2019-0408
Language:
English
Publisher:
Walter de Gruyter GmbH
Publication Date:
2020
detail.hit.zdb_id:
2022101-0
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