Feasibility of Amorphous Bonding in Thermoplastic Composites and the Resulting Interlaminar Residual Stresses

During rapid processing of thermoplastic composites, such as automated fiber placement manufacturing, crystallization is suspected to limit full polymer healing on the interfaces. Reptation theory suggests that interdiffusion can persist until temperature falls below the glass transition temperature in amorphous polymers; however, studies indicate that a critical crystallization value hinders interdiffusion for semi-crystalline polymers. This motivates the incorporation of a thin (5-20 μm) polyetherimide layer between low-melting polyaryletherketone interfaces. This paper will share results of vacuum bag-only processing fabricated short beam strength samples with varied thermal histories. Specifically, this work investigates the feasibility of processing the amorphous interfaces below the melt temperature of the semi-crystalline layer to prevent crystal melting during processing. It also examines the theoretical development of residual stresses, based on classical laminate theory, arising from mismatches in the coefficient of thermal expansion between the two polymers. In conclusion, this paper presents a novel approach to thermoplastic composite processing that could facilitate high-rate manufacturing and also sheds light on mechanics of failure in such samples.