Notch stress and mean stress under fatigue loading of short fibre reinforced thermoplastic polymers

Thermoplastic polymers have a high lightweight potential and used in the automotive- or in the white goods industry in highly loaded application. To scope the best lightweight potential the components have notched section on which have to be paid special attention during the design process. Often the components used in a wide temperature range and in some cases the glass transition temperature is in this usage range.
Below the glass transition temperature, the material has more brittle properties and above the glass transition temperature the material has more ductile properties. Particularly critical is this change in the material properties in notched sections. There, a significant effect of the glass transition temperature to the notch effect was detected. Below the glass transition temperature, a higher notch effect was investigated than above the glass transition temperature.
Based on these findings, the authors analysed 120 S/N-curves of different engineering semi-crystalline thermoplastics materials. In this paper the influence of the glass transition temperature on the notch effect and the mean stress under cyclic loading was investigated. Therefore, several engineering parameters such as stress concentration factor, temperature, conditioning, load ratio, constant and variable amplitude loading were analysed.