Improvement of interfacial strength in overmolded hybrid structures comprising short fiber-reinforced thermoplastics on unidirectional continuous fiber-reinforced thermosets through various surface modifications

Combining pultruded structures made of continuous unidirectional glass fiber reinforced plastic (UD-GFRP) with short glass fiber reinforced polyamide (PA6.6 GF30) by means of injection molding, it is possible to produce cost-effective highly loadable structural components. However, this material combination leads to issues concerning the adhesion. To improve the interfacial bonding between the PA6.6 GF30 and the UD-GFRP, different surface pretreatment technologies are employed. The aim is to investigate and improve the bonding strength to ensure a proper load transfer and a significantly resistant interface to make the material combination suitable for high load applications. In addition to quasi-static pull-out tests under standard conditions, tests are conducted after conditioning and at elevated temperatures. Furthermore, to identify the interlaminar shear strength (ILSS) without an edge effect, short three-point bending tests are performed. The results indicate that adhesion can be significantly enhanced when the thermoplastic bonds with the reinforcing fibers of the thermoset. Additionally, the findings demonstrate that the interfacial strength is considerably higher than measured in tensile shear tests. This study provides a foundation for the potential application of thermoset-thermoplastic hybrids in high load applications within the chassis area. • Without adhesion improvement measures, no bond between thermoset and thermoplastic can be achieved using an intrinsic joining process. • The combination of free fiber exposure and preheating the thermoset to >200°C results in a shear strength of >20 MPa. • The edge effect has a significant influence on the strength of the hybrid composite.