Tensile and fatigue behaviors of polymers for automotive applications

Abstract

An experimental study was conducted on tensile and fatigue behaviors of two unreinforced polymers and two short glass fiber reinforced polymer composites. A number of effects including anisotropy, strain rate and temperature on tensile behavior was investigated. Fatigue behavior was evaluated with respect to effects of mold flow direction, temperature, mean stress, and stress concentration. Effect of mold flow direction on both tensile and fatigue behaviors of unreinforced materials was found to be negligible, while it was significant for reinforced materials. Tsai-Hill criterion commonly used for continuous fiber composites was used to predict the offaxis fatigue strengths of short fiber reinforced materials. Effect of strain rate on tensile properties was found to be significant for all materials. Test temperature also influenced tensile and fatigue behaviors of both unreinforced and reinforced materials. Mathematical equations were developed to represent variations of tensile properties with both temperature and strain rate. Walker equation with a mean stress correction parameter is proposed to correct for the effect of mean stress. Effect of stress concentration combined with mold flow direction and mean stress was also investigated and Neuber's rule resulted in accurate estimation of fatigue life. Keywords: Tensile behavior / fatigue behavior / polymer fatigue / thermoplastic / short fiber composite Schlüsselwörter: Zähigkeitsverhalten / Ermüdungsverhalten / Polymerermüdung / thermoplastisch / Kurzfaser-Verbundwerkstoff Corresponding author: A. Fatemi, The University of Toledo,

Tensile, creep and fatigue behaviours of short fibre reinforced polymer composites at elevated temperatures: a literature survey

“…It can also be observed that the temperature effect is similar for different orientations . Similar stress–strain behaviours has been observed for other SFRPCs at temperatures below and above T g …”

“…Elastic modulus, tensile strength and yield strength decrease almost linearly with increasing temperature for temperatures below and above T g , but with different slopes . Near T g , a drastic reduction in tensile strength and elastic modulus for most of the materials has been observed, an example of which is shown in Fig. for 30 wt% short glass fibre reinforced polybutylene terephthalate (PBT) with T g of about 60 °C .…”

Effects of mean stress and stress concentration on fatigue behavior of short fiber reinforced polymer composites

“…Fatigue life correlation of notched specimens of PBT under fully reversed ( R = −1) condition in the (a) longitudinal and (b) transverse directions, and (c) PP in the transverse direction based on FEA notch root stress, Neuber's rule, and theory of critical distance method.…”

Fatigue behavior and modeling of short fiber reinforced polymer composites including anisotropy and temperature effects

“…A fatigue life prediction model is also applied to all fatigue data to account for the effects of temperature, fiber orientation angle, and stress ratio. Tensile behaviors of the considered materials were characterized and modeled through conducting tensile tests in a range of temperatures and strain rates on samples prepared in several mold flow directions in [28,29]. The effect of moisture on tensile and fatigue behaviors of these materials was also investigated in [30].…”