Fracture toughness characterization of carbon fiber‐reinforced thermoplastic composites under ultrasonic frequency

Abstract The separation and evaluation of fiber layers with residual polymers are pivotal processes within materials‐circularity strategies in composites. Among these, ultrasonic‐assisted methods are significantly faster and more efficient for separating fiber layers of varying thicknesses as they exert less force. This study introduces a novel ultrasonic‐assisted layer separation setup, which integrates stepper motors and a handheld ultrasonic welding system with a resonance frequency of 35 kHz. This system is equipped with a wedge‐shaped cutting tool designed to closely mimic the mechanics of a wedge‐loaded double cantilever beam (DCB) test with few exceptions. The fracture toughness of the carbon fiber‐reinforced PEEK composite material under investigation was analyzed using a theoretical framework. This approach utilized measured horizontal forces and optically monitored effective crack length to derive the toughness values. The findings reveal that fracture toughness decreases as the loading rates increase, with specimen width exerting minimal influence on the outcomes. Furthermore, under high‐frequency dynamic loading conditions, the fracture toughness was nearly reduced by 50% when compared to values obtained using traditional DCB testing methods. This underscores the sensitivity of composite toughness when exposed to high‐frequency ultrasonic oscillations. Highlights Ultrasonic‐assisted layer separation is used for separating fiber layers. The developed system closely resembles the wedge‐loaded DCB (WDCB) test. Fracture toughness is evaluated by a theoretical approach using WDCB mechanics. High‐loading rate influences the fracture toughness. Fracture toughness under ultrasonic oscillation is halved compared to standard DCB test.