Effects of Surface Characteristics on Mechanical and Dielectric Properties of Adhesively Bonded Carbon Fiber Composites

The rapid rise of fiber reinforced composite usage in aircraft, spacecraft and automobile industries made the proper comprehension of repair and joining of these materials a crucial aspect. Adhesive bonding is one of the most advantageous and desirable joining and repair technique for fiber reinforced composites. However, the heterogeneity of fiber reinforced composites and the complex interfacial nature of the adhesive bonds, makes most non-destructive evaluation and assessment techniques ineffective to assess the state of the bond. Different manufacturing and surface preparation techniques impart different surface characteristics to the adherends, hence proper understanding of the state of bonds is dependent upon the characteristics of the adherend surfaces. In this approach, carbon fiber composite adherends with controlled surface modifications were made into lap-shear test specimens using film adhesive. The effects of surface characteristics such as surface roughness and surface free energy of the adherend surfaces, on bond performance are studied. These surface characteristics are found to be an indicator of bond performance and can even be used to explain failure modes. Moreover, the performance of these bonds with varying surface characteristics are analyzed non-destructively by dielectric spectroscopy and compared with the mechanical performance of the bonds.