Adhesive layer analysis for scarf bonded joint in CFRE composites modified with MWCNTs under tensile and fatigue loads

The effects of bondline thicknesses (0.17 & 0.25-mm) and scarf angles (5° & 10°) on the tensile and fatigue properties are investigated, for the first time, for carbon-fiber/epoxy composites scarf adhesive joints (SAJs) modified with optimum weight percentages of multi-walled carbon nanotubes (CNTs). New experimental/analytical model was developed to measure the adhesive displacement parallel to the adherend surface (Δux) using instrumented specimens with extensometer and strain-gauge. The measured values of Δux were used to determine the deformations, normal stresses, in-plane shear stresses and Young's moduli of the adhesive layers in the SAJs under tensile loads. Results from tensile tests showed remarkable increase in apparent and local stiffnesses for the SAJs with CNT-adhesive, 0.17-mm bondline thickness and 10°-scarf angle. The Young's moduli of the adhesive layers of the 5°-SAJs is about 2-3.2 times higher than that of bulk adhesives. The tensile strength of CNT-SAJs is 15.9-33% higher than that of the neat-SAJs with different bondline thicknesses and scarf angles. On the other hand, CNTs have marginal effect on the fatigue strength at lower lives and insignificant effect at fatigue limits (107-cycles). The fatigue strength/life of the SAJs was improved with decreasing scarf angle from 10° to 5° and bondline thickness from 0.25-mm to 0.17-mm.