The Effect of Different Chemical Surface-Modified Carbon Fiber Structure and Ratio on Bond Strength in Adhesive Joints

Abstract

The adhesive bonding techniques are widely used for assembling composite structures with complex geometries due to their several advantages compared to conventional bonding techniques. The present study is concerned with improving the interfacial interactions between fiber and epoxy matrix by reinforcing the adhesive with fiber structures and treating these fiber structures with different chemical surface modifications to improve the performance of the bonded joints. In this study, two different adhesives (rigid and flexible) were reinforced with carbon fibers at 0.5 %, 1 %, 2 %, and 3 % by weight, and the performance of single-lap joints obtained with these adhesives was investigated. Furthermore, a variety of surface modifications were applied to the carbon fibers, including acetone (C3H6O), sulfuric acid (H2SO4), nitric acid (HNO3), hydrochloric acid (HCl), and a mixture of nitric acid and hydrochloric acid (HNO3/HCl). Consequently, the direct incorporation of acetone-treated fibers into the epoxy matrix significantly increased the standard deviation in bonding tests, with values ranging between approximately 12 % and 21 %. However, when acetone was used to reduce the epoxy matrix viscosity before adding the fibers, the standard deviation among test samples decreased to as low as 1.5 %. Moreover, the addition of chemically modified fibers to the adhesive improved the performance of the joints by approximately 4 %-126 %, depending on the type of chemical surface modifier and the type of adhesive used. Based on the bonding test results, the optimal fiber content for the adhesive was determined to be 1 %. To further interpret these findings, scanning electron microscopy (SEM), Fourier-Transform Infrared Spectroscopy (FTIR), and fracture surface analysis were conducted.