Short and long term creep behaviour of polyamide ropes for mooring applications

Abstract

Polyamide 6 fibres are of interest for mooring lines of floating wind turbines and these are continuously loaded throughout their service life. Such applications require the long term response of polyamide 6 ropes in water to be characterized. This paper presents results describing the long term creep behaviour of polyamide 6 sub-ropes with tests that lasted 2 years. A specially designed experimental set-up for long term creep test in water is presented first. Then, a kinetic study comparing creep and recovery is performed using a logarithmic identification of the strain rate. The need for performing long term creep tests is evaluated by comparing the long term creep results to those from short term creep tests lasting 3 h. The results show that a 3 h long creep test provides a reasonable prediction of long term creep strain using a single logarithmic linear law. Finally, a latch-based Weibull model is compared to a single linear logarithmic law to describe and predict creep and recovery response. It is shown that the Weibull model allows a better description of the recovery behaviour of polyamide 6 but is less well adapted for the description of creep.