On the use of milled shell-only specimens to study the effect of fiber orientation on the fatigue behavior of a short fiber-reinforced polyamide

The interpretation of the fiber orientation effects on the fatigue behavior of short fiber-reinforced polymers using specimens extracted from injection-molded plates is hampered by the typical shell-core-shell structure, which affects the stress distribution through the sample's thickness. In this work, local fatigue strength values are obtained using specimens machined to leave only the outer shell layers, thus having a more homogeneous fiber orientation. Results of the finite element analysis of integer and shell-only specimens, accounting for locally measured fiber orientations, are compared. Conclusions are drawn about the role of the core layer and the limitations of milled specimens in the evaluation of the fatigue strength.