Laser-based pretreatment of composite T-joints for improved pull-off strength and toughness

Abstract

This study demonstrates the efficiency of two CO surface laser treatment strategies for improving the strength and toughness of the adhesive bonding of T-joints. The first strategy involves uniform laser treatment to the surface, and the second strategy involves laser patterning by alternatively applying high- and low-power laser irradiation to the T-joint stiffener and skin surfaces. All the laser-treated T-joints showed progressive failure modes during pull-off test, unlike the PP surface-treated joints that exhibited brittle failure. The uniform laser-treated joints exhibited improved strength and toughness because contaminants were removed and the fibers were exposed to be directly bonded with adhesive. The joints subjected to the laser-patterning strategy demonstrated a substantial improvement in terms of the strength and toughness, reaching values of 2.2 and 12 times those of the PP surface-treated T-joints, respectively. This is because of the crack arresting at the transition between the two treatments at the stiffener interface, inducing crack migration from the stiffener-adhesive interface to the skin-adhesive interface while forming adhesive ligaments. The formation, deformation, and breakage of these ligaments dissipated more energy, hence increasing the effective joint toughness and strength.