Characterisation by indentation of glass / polyester composites: effect of the resin polymerisation process

http://euromat2017.fems.eu/programme/final-scientific-program/For several years, the use of photochemical resins to produce composites has encountered problems related to the manufacturing process. It is clear that the UV rays could be dangerous, but the difficulty of controlling the flux, and its penetration within the composite, make impossible to keep the percentage of polymerised resin under control. Recently, some advanced technologies using robot-based deposition systems and the introduction of LED lamps have put again this technology forward. It is well known that the progress of the resin polymerization have a strong influence on the mechanical behavior. The purpose of this work is to present and compare the mechanical properties of unidirectional glass / polyester composites. Two different processes: conventional thermal polymerization and photochemical polymerization were used to polymerize the polyester resin. The surface mechanical properties were studied by micro-indentation carried out with a Berkovich indenter under a maximum load of 500 mN. The speed of charge and discharge and the time during that the maximum load remains constant was chosen to analyze the creep behavior of the material. The indentation hardness HIT is not sufficient to discriminate the samples. Elasticity and viscoelasticity properties are necessary to compare the differen composites. For the composites elaborated by thermal polymerization, a post curing step improves the hardness and decreases the creep. For photo cured composites, a long step of vacuum allows a better fiber impregnation by the resin. As a consequence, the hardness and stiffness of the structure are enhanced. Finally, this work shows that photopolymerised composites exhibit better mechanical properties compared to conventional one obtained by thermal process. The differences in hardness and indentation modulus are quantified and related to the elaboration proces