The primary objective of this study is to determine the interphase behaviour of a thermoset epoxy resin that is commercially used for carbon fibre–reinforced composite materials in aerospace structures and a suitable thermoplastic material that can be used as a boundary layer. The thermoplastic boundary layer will be used for welding purposes to join structural components with a fraction of the effort compared to conventional gluing processes. In this study, the interphase formation of an epoxy resin with several thermoplastic materials, namely, polyetheretherketone, polyvinylidenfluoride, polyphenylensulfide and polyetherimide (PEI), is studied via hot-stage microscope experiments. Based on this study, PEI was selected, and a detailed study was performed to determine the dependency of dissolution, diffusion and phase separation mechanisms under various isothermal conditions. Additionally, the welding behaviour was investigated by a resistance welding rig whereby the process parameters were statistically varied to optimize the lap shear strength. The results of this study will enable a statement about the interphase development, the morphology and the mechanical properties which is a key element of fully understanding the process.

Epoxy resins have several applications in the aerospace and automobile industry. Because of their good adhesive properties, superior mechanical, chemical and thermal properties, and resistance to fatigue and microcracking, they produce high performance composites. Since it is necessary to optimize the manufacturing time and costs and to determine the performance of these composites, some researchers [1][2][3][4] have studied infrared (IR) heating for the polymerization process. Others [5,6] have used IR energy for the preheating process.In the technology presented here, the composite is cured in an IR oven (see Figure 1) which includes halogen lamps. The liquid resin infusion (LRI) process is used to manufacture the composite, whereby liquid resin is infused through a fiber reinforcement previously laid up in a one-sided mold.These epoxy resins release an exothermic heat flux during the curing process, which can possibly cause an excessive temperature in the thickness. Consequently, for the production of high performance composites, it is necessary to know the thermal behavior of the composite during curing. The most detailed models for the curing process of composites using IR heaters have been presented by Chern et al. [1][2][3][4] They measured the radiative properties of graphite/epoxy and glass/epoxy systems and modeled the radiative heat transfer in the glass/epoxy system as a volumetric radiation transport. Therefore, IR interactions with the graphite/epoxy system were modeled as a surface radiation transport.Cosson et al. [7] developed numerical algorithms, based on a ray-tracing method. In-lab software, called Rayheat, predicts the volumetric distribution of the radiation intensity in a semi transparent medium. This software also models IR interactions with highly absorptive mediums, where the radiation transport is a surface radiation. In this paper, we present simulations of the IR curing process of a carbon/epoxy system. Numerical simulations were performed in order to determine the temperature distribution in the composite thickness during the polymerization process. The heat balance equation is coupled with the exothermic heat and the radiative heat flux using the commercial software Comsol Multiphysics TM . In order to introduce these simulations to an industrial composite part, we validate the simulations of a simple sheet of composite. Liquid Resin Infusion (LRI)LRI is used for the impregnation process of fibers with resin. In this process, presented schematically in Figure 2, liquid resin with low viscosity is infused through fiber reinforcement, which is placed in a single-sided mold sealed with a vacuum bag. Before being impregnated by resin, the fiber reinforcement must be preheated by the IR lamps, in order to maintain the low viscosity of the resin and to facilitate its path through the reinforcement. This process combines the advantage of infusion at ambient pressure, short cycle time and low cost equipment with the ability to produce parts of COMMUNICATION [**] Grateful acknowledgement to...

Because of higher specific strength and stiffness, low weight, and good resistance to corrosion, the use of composite materials in aerospace structures has increased. Aircraft industry has recently begun to investigate Liquid Composites Molding techniques (LCM) through research programs because of its ability to produce large parts at a low cost. In this paper, we have not addressed the filling step during which the resin flows through fibrous media, but we investigate the numerical simulation of curing reinforced RTM-6 by infrared heating. Finite element based program COMSOL Multiphysics™ has been used to simulate the curing process. Thermochemical model has been implemented in order to compute reaction rate as a function of reaction temperature and degree of conversion using a cure kinetic model .