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The “Notched Cylindrical Bars Under Constant Load Test” (NCBT) as a Means to Assess the Resistance to Crack Initiation and to Slow Crack Growth of PE100 and PE100 RC

 

Papers # 2014 Chicago

The emergence of a new generation of PE100, named PE100 RC, with a significant enhanced Slow Crack Growth (SCG) resistance enlights the need for new testing methods in order to be able to test such resins in reasonable test durations. Consequently in the last five years some new tests have been designed to assess for SCG behavior, as for example the Strain Hardening Test (SHT) and the Cyclic Crack Round Bar Test (CCRBT). Aside to the progress of round robin tests, these experimental procedures are currently discussed as draft standards in the ISO TC138-SC5-WG20 committee. In this framework and given its long experience with a modified version of the Full Notch Creep Test – referred to as NCBT – applied on PE63 and PE80 since the early nineties, GDF SUEZ Research & Technology Division has proposed to the SCG working group to evaluate the potentialities of the NCBT procedure to characterize the PE100 and the PE100 RC in a reasonable test duration less than 1,000h. Both the experimental conditions and the theoretical interpretation of the NCBT procedure differ significantly with regards to the classical FNCT as supported by the ISO 16770 standard. In order to evaluate the NCBT procedure, two PE100 and two PE100 RC have been chosen among the resins produced by the PE100+ Association members. From the results, first it is shown that the ratio of the initiation time and the failure time remains quite constant, independently of the PE tested. Secondly it is possible to detect a Slow Crack initiation time within a 500h test duration or less. Third, a ranking of the four PEs can be done in a common accessible stress range. In order to better understand the SCG differences of the four PEs, both HLMI and DSC-SIS experiments have been carried out on the basis of the procedure designed by GDF SUEZ R&T Division. Some keys elements are deduced form HLMI and SIS evaluation for the understanding of the significantly different NCBT behaviors of one PE100 and one PE100 RC of the set.

Related keywords : pe100, time, stress, initiation, times, level, crack.
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