Experimental investigation on the true local fatigue strength of shell-core shell layered, injection moulded specimens of short fibre reinforced polyamide

Injection moulded plates made of short fibre reinforced polymers are often used to study the effect of fibre orientation on mechanical properties. Using specimens cut out of these plates with different orientations with respect to the injection flow, off axis tests can be performed. However, injection moulded plates have a characteristic layered structure, with different fibre orientations through the thickness, resulting into the well-known shell-core-shell structure. This makes it difficult to separate the contributions of each layer. In this work, a preliminary study on the fatigue behaviour each layer is presented. Specimens were machined by milling, leaving only the shell layer in specimens extracted from plates at 0° and 90° orientations. Results are discussed in the light of finite element analysis, where the layered microstructure is considered. For the simulations, fibre orientation distributions obtained experimentally are used and stresses in each layer are evaluated. Finally, local stresses are compared with local strength values obtained experimentally.