Modeling-based characterization for thermal expansion and chemical shrinkage of highly viscous epoxy resin with thermoplastic additives under the curing condition

The present investigation introduced an indirect approach to accurately characterize thermal expansion and chemical shrinkage coefficients of the BA9916 resin, which is a thermoset epoxy resin with thermoplastic additives for enhanced impact performance, throughout the curing process. To ensure modeling accuracy, experimental measurements of thermal decomposition and curing kinetics were also considered. Characterization of the BA9916 resin based on experiments completely was difficult due to its exceptionally high viscosity caused by the thermoplastic additives, imposing major obstacles in degassing during sample preparation. To tackle this problem, an indirect characterization method was utilized, beginning with characterizing the unidirectional (UD) composites with the BA9916 resin. Based on the measured composite properties, the corresponding characteristics of the BA9916 resin were then calculated using the modulus-modified rule-of-mixtures with carbon fiber reinforcement properties provided by the material supplier. Subsequently, the representative volume element (RVE) models for the UD composites with various configurations, including different volume fractions of carbon fibers, degrees of curing and curing temperature profiles, were established for simulation with the theoretically calculated resin properties and supplier-provided fiber characteristics. Homogenized results of the RVE modeling were validated against the experimental measurements with an error of less than 6%, demonstrating the effectiveness of this modeling-based method for characterizing the coefficients of thermal expansion (CTE) and chemical shrinkage (CSC) of the highly viscous thermoset resin under the curing condition. Highlights: The resin is a thermoset epoxy resin toughened using thermoplastic additives. The excessive viscosity of the resin hindered effective degassing. The thermo-chemical properties of the resin were characterized indirectly. A non-contact approach was used to determine the CTE and CSC.