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Revisiting creep test on polyethylene pipe—Data analysis and deformation mechanisms
Polymer Engineering and Science ( IF 3.2 ) Pub Date : 2020-12-14 , DOI: 10.1002/pen.25603
Pean‐Yue Ben Jar 1
Affiliation  

Creep tests have long been used to determine long‐term hydrostatic strength (LTHS) for polyethylene (PE) pipe. In view that current standard requires some long‐term creep tests of over 9000 h to determine LTHS, this paper explores the possibility of using relatively short‐term creep tests for the same purpose. The study found that trend line for applied stress versus failure time changes at the failure time around 10 h, and the data trend in the low‐stress regime is consistent with that from the standard test. The trend line change is believed to be caused by the change of the involvement of amorphous and crystalline phases in PE in the deformation process, that is, sequential involvement of the amorphous phase first and then the crystalline phase in the low‐stress regime, and simultaneous involvement of both phases from the beginning in the high‐stress regime. Activation energies based on the Eyring's model and the Norton power law are determined to examine the proposed concept. Both models suggest that additional activation energy is needed for deformation in the high‐stress regime, which provides some support to the proposed concept and the possibility of using short‐term creep tests to determine LTHS.

中文翻译:

聚乙烯管材再蠕变试验—数据分析与变形机理

蠕变测试长期以来一直用于确定聚乙烯(PE)管的长期静水强度(LTHS)。鉴于当前标准需要进行9000 h以上的长期蠕变测试才能确定LTHS,因此本文探讨了出于相同目的使用相对短期蠕变测试的可能性。研究发现,施加应力与失效时间的趋势线在失效时间约10 h时发生变化,并且低应力状态下的数据趋势与标准测试的趋势一致。据认为,趋势线的变化是由于PE在变形过程中非晶相和结晶相的参与变化引起的,也就是说,在低应力状态下,非晶相先相继参与,然后结晶相依次参与,并从高压力时期开始就同时参与两个阶段。确定基于Eyring模型和诺顿幂定律的活化能,以研究提出的概念。两种模型都表明,在高应力状态下变形需要额外的活化能,这为所提出的概念提供了一定的支持,并为使用短期蠕变测试确定LTHS提供了可能。
更新日期:2021-02-08
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