Effect of temperature aging of thermoset UD prepregs on inter‐ply friction behavior and formability in prepreg compression molding process

Abstract Limited material out‐life of thermoset prepregs is unavoidable attributed to the slow crosslinking reaction between molecules and curing agents. Previous studies have explored the effects of temperature aging on the final mechanical properties of composites, but have been limited by the processing mismatch in compression molding. The research primarily focuses on the effects of forming temperature and ply angle of prepreg on inter‐ply friction behavior at various aging levels. The importance of inter‐ply friction on the forming quality is further discussed through the L‐shaped specimens forming with prepreg compression molding (PCM) process. Firstly, a comprehensive influence of aging on the properties of resin including cure kinetics, gel point, glass transition temperature (T g ) and viscosity of UD prepreg are characterized and discussed. And then, the influence of factors including resin aging, forming temperature and prepreg ply orientation on the inter‐ply friction are discussed. It can be found that the aging of prepreg reduce 26.47% of inter‐ply friction resistance under room temperature, and the increase of temperature can reduce inter‐ply friction resistance by 79.31%. Finally, the effect of aging on the forming quality is researched by PCM formed L‐shaped components. Results indicated that fresh prepreg with 20°C and prepreg with an aging level of 0.4 performed at 95°C exhibited poor formability, while prepreg with aging level of 0.2 at 95°C exhibited the best forming property. In general, this study provides a basic explain and a practical suggestion to the reuse of room temperature aging thermoset prepregs in PCM process. Highlights A comprehensive of basic properties of aged resin were characterized, as the basic principle for inter‐ply friction behavior analysis. The gel point and final mechanical properties of prepreg were tested, for judging the aged materials whether could be used continuously. The inter‐ply friction behaviors of aged prepregs under various forming temperatures were investigated. The influence of layup orientations on the inter‐ply frictional performance with various aging levels were explored. The effect of aging and forming temperature on the PCM formability were studied and a practical suggestion to the reuse of aged thermoset prepregs in PCM process was given.