Temperature effects on creep behavior of continuous fiber GMT composites

The effects of temperature on the tensile creep of continuous random fiber glass mat thermoplastic composite (GMT) have been studied following an accelerated characterization procedure. The objectives of this work are twofold. First, is to obtain a long-term creep model using time–temperature superposition (TTS) that can represent behavior within the linear viscoelastic regime (up to 20 MPa) at room temperature. The second is to develop a non-linear viscoelastic model that accounts for a wide range of stresses and temperatures. Creep and recovery tests were carried out for a stress range between 20 and 60 MPa over a temperature range of room temperature to 90 °C. TTS was applied to obtain a master curve which was curve fitted to a nine-term Prony series. It was found that material generally behaved non-linearly for all stresses and temperature. For stresses up to 50 MPa, the non-linear viscoelastic behavior due to temperature can be reasonably modeled by only the time–temperature shift factors from TTS. At 60 MPa, however, the non-linear parameters have to be modeled as a product of stress and temperature dependent functions. The model predictions are in good agreement with the experimental results at most stress and temperature levels. The creep curves predicted at higher temperatures especially at 60 MPa tend to underestimate at longer times.