Step and scarf joint elastic and failure behavior comparison under tensile and flexural loading

Abstract

Step and scarf joints are the two most commonly used joint types in composite laminate bonding, offering distinct characteristics and behavior in response to specific loading conditions. In order to gain a comprehensive understanding of the mechanical behavior step and scarf joints, a comparative study of adhesive bonded step and scarf joint carbon fiber reinforced composite laminate under tensile and flexural loading condition was performed. The test specimens were fabricated with carbon fiber reinforced composite laminate. The step and scarf joints were precisely manufactured using a precise milling machine, and the joints were bonded with an epoxy adhesive with controlled bondline thickness. To assess the behavior of the bonded joint structure under various loading scenarios, both tensile and four-point bending flexural tests were performed. Strain measurement during these tests was carried out using digital image correlation (DIC) technology. The step joint showed multiple sequential bondline crack propagations while the scarf joint experienced a single catastrophic failure. The test result showed that the step joint retained 10% and the scarf joint retained 32% of tensile strength compared to the no-joint test specimen. Also, the step joint retained 13% and the scarf joint retained 44% of flexural strength compared to the no-joint test specimen. As a result, the scarf joint had significantly higher ultimate tensile strength, tensile modulus, and tensile strain at failure. The scarf joint also showed higher ultimate flexural strength and flexural modulus compared to the step joint.