An investigation into the long-term viscoelastic recovery of Nylon 6,6 fibres through accelerated ageing

As part of investigations into the development of viscoelastically prestressed polymeric matrix composites, time–temperature superposition principles have been adopted to evaluate the long-term viscoelastic strain recovery characteristics of nylon 6,6 fibres. Annealed samples of yarn were subjected to a 24 h creep loading, followed by recovery, initially under normal ambient temperature (∼20 °C). The samples were then subjected to several increasingly long periods of exposure to 60 °C, which enabled recovery strain to be evaluated over the equivalent of 9 × 105 h (100 years). Results provide good agreement with (i) previously obtained recovery data measured in real time for up to 3.5 × 104 h (4 years) and (ii) a predictive model, based on data from (i). Moreover, the contribution to strain from viscous flow effects is indicated to be less than 10−4%. The findings are supported by tests on composite samples, in that no significant deterioration in impact performance was observed, after being subjected to similar conditions of accelerated ageing.