Flexural creep behaviour of long glass fibre reinforced polyamide 6.6 under thermal-oxidative environment

This article aims to investigate the flexural creep behaviour as a function of temperature of long glass fibre polyamide 6.6 taking into account the thermal-oxidative degradation occurring during the test. The mould geometry has been chosen so as to reproduce some geometrical accidents (e.g. sharp frontal and tangential steps) occurring on industrial moulds. The nominal fibre content (10, 40 and 55wt%), initial fibre length (short glass fibre, long glass fibre), load rate (up to 70%) and creep temperature (23?, 100? and 130?) have been considered to estimate the Findley's model coefficients. A first investigation on the polyamide 6.6 degradation under thermo-oxidative environment has been led to understand the mechanisms of thermal-degradation of the polyamide 6.6 composites. The pure polyamide 6.6 matrix has shown a 20% increase of flexural modulus during the first period of ageing attributed to a combined chain scissions and cross-linking reactions. Then, a decrease of properties attributed to predominant chain scission mechanism was noticed after 1000h of thermal exposure reaching up to 30% after 5000h. In case of reinforced polyamide 6.6, the flexural properties tend to increase (+6.5%) up to 2000h of exposure. The least square method has then permitted to evaluate the material coefficients from the experimental data; the instantaneous creep strain has been estimated from a power law representation. In any cases, the calculations are in a good accordance with experimental measurements.