A comparison of gel point for a glass/epoxy composite and a neat epoxy material during isothermal curing

Determination of gel point is important for a modelling assessment of residual stresses developed during curing of composite materials. Residual stresses in a composite structure may have a detrimental effect on its mechanical performance and compromise its integrity. In this article, the evolution in bending stiffness of a glass/epoxy composite material during an isothermal curing process is examined to identify different material stages and behaviour. Differential scanning calorimetry and dynamic mechanical analysis are used to analyse the material behaviour. Gelation is identified as a clear onset in bending stiffness, and vitrification is seen as a decrease in the bending stiffness rate. Often gel point predictions for composite materials are based on neat matrix measurements. However, the results presented in this article demonstrate that the gel point is affected by the presence of the fibre reinforcement.