Abstract
The flex fatigue of nylon and polyester fibres is measured by pulling them backwards and forwards over a pin in an environmental chamber. The fatigue lives vary over a 20-fold range as temperature and humidity changes. For nylon 6, the plots show a consistent increase to a maximum value and then a decrease as the temperature is increased from 20–120 °C. The peak lifetimes occur at higher temperatures at lower humidities. The results for nylon 6.6 show peaks at intermediate humidities, but little change at low and high humidities. The peak life temperature increases as humidity decreases for nylon 6.6, but is unchanged for polyester. The nylon 6 results follow the same trend as the loss modulus in variation with temperature and humidity, with a high loss correlating with a long life. A possible reason for this and the influence of other complicating factors, are discussed.