Effects of top ply orientation and a resin-rich interface layer on the strength of LMPAEK-CF/PEEK-CF overmoulded joints

Abstract

The effects of the top ply orientation and the addition of a resin-rich laminate surface layer on the quasi-static and fatigue strength of overmoulded composite joints were investigated experimentally. Therefore, rib coupons with varied laminate configurations were manufactured in a dual-step overmoulding process. The coupons, made from short carbon fibre-filled PEEK and unidirectional continuous carbon fibre-reinforced LMPAEK, were subjected to a rib-pull-off test. The additional resin-rich surface layer on the laminate significantly increased the pull-off strength and equalised the effect of the top ply orientation. Without the resin-rich interlayer, a significant effect of the top ply orientation was observed. With the top ply being oriented perpendicular to the rib, failure occurred mostly in the interface, while higher pull-off strength was associated with the fibres running parallel to the rib. This was attributed to a predominant laminate failure mode. A new interfacial void pattern was observed to a larger extent in specimens with the resin-rich interlayer and a hypothesis for its genesis is presented. Compared to monotonic, quasi-static loading, the cyclic fatigue loading up to 106 cycles resulted in a typical overall reduction of the ultimate pull-off strength. However, the strengthening effect of the resin-rich layer and the effect of the top ply orientation persisted also under cyclic fatigue loading.