Method development for the mechanical characterisation of cathodic electrodeposition coatings for numerical simulation of bonded joints

This paper describes the development of a method concept for the mechanical characterisation of cathodic electrodeposition (CED) coatings in the context of adhesively bonded joints. The objective is to determine mechanical properties of coating layer in order to incorporate its influence into numerical simulation models for load-bearing adhesive joints. For this purpose, both single-lap joints (SLJ) and modified thick adherend shear specimens (TASS) with defined CED coating layers were produced and tested under quasi-static loading conditions. Additionally, the deposition process was analysed in terms of coating thickness evolution as a function of deposition time and applied voltage. The specimens were pre-cured to reduce gas inclusions from evaporating solvents in the CED coating layer. The pre-curing temperature was determined using DSC. The results indicate that the modified TASS configuration is particularly suited for the reproducible evaluation of the shear load-bearing capacity. In comparison to the SLJ, it favours the degassing of solvents through the installation of grooves. Furthermore, it is demonstrated that gas-induced defect zones originating from the electrochemical deposition process significantly compromise joint performance. The experimental and process methodology developed in this study enables isolated characterisation of the coating layer and provides a solid foundation for simulation of coated adhesive joints.