Interfacial enhancement of CFRP/titanium alloy bonding joint by constructing a 3D interconnected CNTs network

Abstract

Carbon fiber-reinforced polymer (CFRP)/titanium alloy joints offer exceptionally lightweight, superior fatigue behavior and impact resistance for aerospace applications. Nevertheless, Fiber-tear failure manifestly occurs in the CFRP/metal bonded joints due to the stress concentration of carbon fiber (CF) surfaces, and the adhesive cannot develop its full shear strength capacity, resulting in low shear strength. This drawback has limited the reliability of CFRP in full-scale structures where adhesive bonding is essential. In this study, a three-dimensional (3D) interconnected carbon nanotubes (CNTs) network was constructed on the CFs on the surface of CFRP to release the stress concentration. Carboxyl functionalized CNTs were grown on the surface of CFs, and then the CNTs were arranged in the adhesive to form a 3D network using ultrasonic-powered adhesive injection (UPAI) process. The interfacial bonding strength can reach up to 29.51 MPa, increasing by 30.7%. The growth of CNTs was verified by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The ultrasonic process can effectively promote the construction of 3D coiled/entangled and vertically aligned CNT structures, providing a more complex crack propagation path for the energy dissipation capability. FESEM and energy dispersive spectroscopy (EDS) tests of the cross sections of CFRP/titanium (Ti) alloy joints revealed that the ultrasonic process promoted mechanical anchoring owing to improved wettability and increased acoustic pressure within the adhesive. These results provide insights into future high-performance CFRP/metal hybrid joining technology of lightweight structures.