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The failure mode termed long time brittle failure (due to slow crack growth – SCG) limits the lifetime of plastic pipes. There are now two main accelerated tests (PENT and FNCT) that enable us to estimate the lifetime of HDPE used in plastics pipes. For unimodal grades, the time to failure corresponding to these accelerated tests is about ten hours, for bimodal grade PE 100 it is roughly a thousand hours and for the new PE 100 RC grade is greater than 1 year. For the HDPE pipes grade with higher resistance against SCG, some modification or, alternatively, new tests should be developed that make it possible even for these materials to obtain the results required in a relatively short time. In this contribution we focus mainly on the PENT test and the possibility of the utilization of a structural analysis as well as a numerical approach for prediction of the lifetime of a new generation of PE grades. |
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