Mechanical properties of Thermoplastic/Thermoset interphases

This master thesis adress the thermoset composite welding process, a promising joining method for the assembly of composite parts for aeronautical application. This process involves the cocuring of the resin with a thermoplastic, leading to a hermoset-thermoplastic (TS-TP) interdiffusion and interphases. Morphology, mechanical properties and fracture behaviour of the RTM6 resin modified by two different thermoplastics with either low and high glass transition temperatures was investigated. Compression and nanoindentation tests were performed on blends of RTM6 with different PEI contents, both showing an improved stiffness and a synergical effect. The morphological characterization of PETT-RTM6 cocured interphases reveal a co-continuous inter-penetrating network , with a sea-island morphology in both TP and TS rich phases, while a nodular structure is observed in the TP rich phase of RTM6-PEI interphases. A control of the interdiffusion length and the the RTM6-PETT cocontinuous network thickness is demonstrated by pre-curing the resin before co-curing it with a PETT layer. An attempt of surface patterning of PEI and PETT layers was carried out respectively by laser etching and 3D printing in order to study the influence of the roughness on the mechanical properties of the resulting TS-TP interphases.