How surfaces of carbon fiber reinforced plastics with thermoset matrices need to be treated for structural adhesive bonding

Abstract

ABSTRACT In this research study two very different surfaces of the same type of a carbon fiber reinforced plastic (CFRP) are deliberately prepared to compare characteristics of the created surfaces and the achieved strength of the adhesively bonded joints. Within this approach, explanatory power of state-of-the-art surface analysis methods, applicability of destructive tests and adhesion mechanisms for high-strength adhesive bonding of CFRP are discussed. One CFRP surface was prepared with a highly optimized atmospheric pressure plasma treatment (APPJ). Another CFRP surface was created with a highly optimized and adjusted vacuum blasting process. Initial CFRP surface and treated CFRP surfaces were characterized with surface analysis methods X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), contact angle measurements and Field-Emission Scanning Electron Microscopy (FE-SEM). Mechanical strengths of adhesive joints were determined with three different destructive test methods (single lap shear, double cantilever beam, centrifugal adhesion test) for all surfaces. Interestingly, the very different surfaces led to adhesive joints with comparable mechanical strength. After a comprehensive discussion, the author isolates relevant adhesion mechanisms for adhesive bonding of surfaces of thermoset polymers. The study concludes with proposals for necessary future research efforts to achieve the aimed reliable high-strength adhesive joints for safety relevant CFRP structures.