A novel and rapid method of integrating sensors for SHM to thermoplastic composites through induction heating

Abstract

A novel, rapid, and efficient method for bonding Piezoceramic transducers (PCTs) to high-performance thermoplastic composites using thermoplastic adhesive films (TPAFs) and induction heating is presented. The current state-of-the-art techniques to bond PCTs to composites using epoxy adhesives can take hours. This innovative out-of-oven or autoclave procedure drastically reduces bonding time to mere minutes, thereby significantly enhancing the process efficiency. Five different TPAFs were used to bond PCTs to carbon fiber polyether-ether-ketone (CF-PEEK) coupons. After determining the process window and analyzing the effects of power, coupling distance, and time on temperature, it was found that power has the greatest influence. A 20% increase in power can result in 50.9% increase in temperature as compared to time. Controlled heating and cooling ramps were developed based on the power-temperature correlation, and their effects were analyzed through differential scanning calorimetry tests. In the controlled case, the melting enthalpy of semi-crystalline TPAF increased by 4.2%, while the glass transition temperature of amorphous TPAF increased by 2.4% compared to non-controlled case. Following successful PCT bonding, mechanical performance was evaluated through static flexural and fatigue tests. TPAFs exhibited critical strains of 0.33%-0.71%, with some exceeding the critical strains of co-bonded or epoxy-bonded PCTs in previous studies by 0.13%. Microscopic analyses revealed the dominant failure mode at the composite-adhesive interface. During fatigue testing, three out of five TPAFs performed successfully, with the highest change in electro-mechanical susceptance spectra observed in amorphous TPAF equivalent to 1.87%. Overall, an efficient methodology is proposed, particularly beneficial for applications in structural health monitoring.