Degree of healing model for vibration-assisted thermal bonding (VATB) of thermoplastic composites

Studies show that thermoplastic composites manufactured using in-situ Automated Fiber Placement (AFP) exhibit lower mechanical properties compared to those consolidated in an autoclave, particularly in terms of interlaminar shear strength and flexural properties. This performance gap can be attributed to the short manufacturing time in the AFP process, which restricts the degree of healing that can be achieved. To address this, vibration-assisted thermal bonding (VATB) was previously proposed as an approach to enhance bonding strength. While promising results were observed, optimizing the VATB process requires a mathematical model for prediction of bonding strength during the manufacturing process. To achieve this, in the current study, a new analytical relation has been developed to predict the bonding strength during VATB process. This theoretical model demonstrates the impact of vibratory consolidation forces on the degree of healing. To validate this model, experiments were conducted to examine the effects of frequency-dependent vibratory pressure on consolidation quality, welding time, and the healing evolution of carbon fiber/poly ether ether ketone (CF/PEEK) thermoplastic composites. The results indicate that substituting static pressure with vibratory pressure significantly improves bonding strength, with increases of up to 85% at 355°C and 22% at 375°C, and reduces welding time—the duration required to achieve maximum strength—by approximately 90% at lower temperatures and 50% at higher temperatures. Additionally, the degree of healing, which is dependent on welding time, is influenced by both the frequency and amplitude of the vibration, with higher frequencies accelerating the healing rate.