Sensitivity of double cantilever beam test to surface contamination and surface pretreatment

The double cantilever beam (DCB) test is one of the commonly used destructive tests to qualify structural adhesives joints. By measuring the force and the corresponding crack growth of the mode I—loaded specimen, the adhesive fracture energy, GICGIC, can be determined. Many parameters like adhesive joint thickness, mechanical properties of the adhesive, substrate thickness and stiffness and production quality influence the results of the DCB test.In this article the influence of surface modification due to contamination and surface pretreatment on the results of DCB tests is investigated. Different amounts of hydraulic oil as a typical surface contamination have been applied to a carbon fiber reinforced plastic (CFRP) substrate. Three different surface pretreatments of the CFRP (peel ply, teflon foil and atmospheric pressure plasma) have been investigated. The surfaces have been characterized by contact angle measurements and atomic force microscopy (AFM). Results of DCB tests are analyzed in relation to the fracture surface and compared with tensile strength results of single lap shear specimens.