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M Palmstingl, D. Salaberger, T. Koch:
"Morphology and fatigue behaviour of short-glass fibre-reinforced polypropylene";
in: "Deformation and fracture behaviour of polymer materials", 247; W. Grellmann, B. Langer (ed.); issued by: Springer Series in Materials Science; Springer International Publishing AG, Cham, 2017, ISBN: 978-3-319-41877-3, 315 - 334.

The fatigue bahaviour of short-glass-fibre-reinforced polypropylene was investigated in dependence on the fibre orientation. For that, a special plate geometry was developed which allows to exclude the effect of machining and leads to original injection surfaces at least in the region of the main (slightly concentrated) load. This "original"surface matches the surface situation of the injection moulded consumer parts. Furthermore, the plates consist a notch region and a knit line. Morphology analysis can be done by sectioning and stereological principles or by X-ray computed tomography. The fatigue strength shows a strong correlation to fibre orientation, but the samples taken from the knit line and the notch region do not follow this correlation. In these regions the situations are more complex. The application of different methods for the characterization of the evolution of damage (development of dissipated energy, strain, normalized modulus, temperature) does not give a clear indication of damage, there are no clear signs of damage until shortly before the fracture. High speed camera in combination with digital image correlation can give information on local strain and therefore on the localized occurrence of damage at a relatively early stage of fatigue life.

polypropylene, short-glass, fibre-reinforced, fatigue