Abstract
Abstract As an important step towards the use of high tenacity polyamide 6 (PA 6) yarn in long-term mooring lines, a good understanding of the creep and recovery behavior of the fiber under constant loading is necessary. Creep and recovery of textile fibers have been the subject of several studies, but test data relevant for water saturated PA6 yarn at different temperatures and loads are scarce. In the work presented here, simple creep-recovery cycles of yarn specimens were performed at loads from 0.1 to 0.26 N/tex (the average tensile strength of the wet yarn at 25°C is 0.69 N/tex) and temperatures from 21 to 42°C. The purpose was to collect data for further analysis and modelling purposes. The paper presents in detail a bespoke rig for creep testing of standard ISO 527 specimens, which was modified to accommodate yarn specimens and their testing at required precision. The specimen manufacture is also presented as this is not a trivial part of the study. Results showed that strain recovery behavior of the yarn post creep could be described by a linear logarithmic equation for all combinations of load and temperature. However, the creep behavior at low loads and the lowest temperatures were best described by a Weibull fit, which for increasing loads gradually shifted towards a linear logarithmic fit. The creep rate was found to be dependent on both load and temperature, whereas the recovery rate was found to be mainly dependent on temperature. The strain recovery rates were almost identical to the linear logarithmic shrinkage rates measured during specimen conditioning. The instantaneous strains after loading and after unloading, i.e. initiation of the recovery phase, exhibited a good correlation.