Low cycle fatigue of short fibre reinforced polyamides

In the automotive sector short-fibre reinforced polyamides play a major role for highly loaded components in under the hood application. In this field of use, the components are subject to different kinds of loading in the high cycle and the low cycle regime. For short-fibre reinforced polymers, especially the low cycle regime could be critical due to the usually moderate slope of the S/N-curve. In the low cycle fatigue regime, the estimation of the load history and the load sequence is a great challenge. Low-cycle fatigue of polymer parts is mainly caused by extreme operating conditions, misuse, temperature changes or other extreme environmental conditions. This paper presents results achieved investigating the low cycle fatigue behaviour of short fibre reinforced polyamides. Two different manufacturing processes, the injection moulding process, and pressing process, have been compared. The manufacturing processes cause local orientation of the reinforcing fibres which leads to anisotropic material properties. Specimens with fibres predominantly oriented at 0° and 90° to the loading direction were used to characterise the effect of fibre-orientation on low cycle fatigue performance. Additionally, the influence of notches on the low cycle fatigue performance is investigated. By means of hysteresis data, the failure mechanism and the crack initiation is analysed.