Measurement of Interfacial Bonding Force between Foam and CFRP in Foam-Cored CFRP Sandwich Composites

Polymer foam, a core material in the foam-cored carbon fiber reinforced polymer (CFRP) sandwich composites, is a low-strength material with porous characteristics and mechanical properties different from those of CFRP. Consequently, the accurate measurement of the material properties, such as the interfacial bonding force between the foam and CFRP of the foam-cored CFRP sandwich composite is difficult. This is because the foam becomes compressed and deformed if fixed by applying pressure, as in the case of the regular method. To mitigate this shortcoming, this study developed a novel test fixture for the measurement of the interfacial bonding force of foam-cored sandwich composites. Furthermore, a forming fixture was devised to uniformly fabricate samples used in the developed test fixture. Using the developed fixture of interfacial bonding force for foam-cored sandwich composites, the interfacial bonding force of CFRP sandwich composites was measured with respect to polymethacrylimide (PMI) foam (thermosetting polymer) and polyethylene terephthalate (PET) foam (thermoplastic polymer). The measured interfacial bonding strength between the PET foam and the CFRP was larger than the tensile strength of the PET foam. In contrast, the interfacial bonding force of PMI foam and CFRP was at the level 20% of the tensile strength of the PMI foam. The microstructures were analyzed using an optical microscope and scanning electron microscope to investigate the cause. According to the results, the bonding area between the PMI foam and the CRFP resin was relatively small compared to that between the PET foam and the CFRP resin. The interfacial bonding force of foam-cored sandwich composites can be measured more accurately using the measurement fixture of the interfacial bonding force and the forming fixture developed in this study.