Cathodic delamination of elastomer-to-metal adhesive joints: Experimental data and empirical modeling

Abstract

In order to estimate the cathodic delamination rates of metal adhesive/steel adhesive bonds, an empirical model based on crack growth is developed. To this end, a considerable amount of delamination data was experimentally collected under several levels of cathodic environmental harshness (some highly accelerated) and applied peel stress. For a given electrolyte, cathodic delamination was found to depend on cathodic voltage (or current density), temperature, and applied strain energy release rate, G. In order to describe the progress of delamination under various cathodic environments as a function of applied G, the collected, experimental delamination-distance-versus-time data were used to develop characteristic curves of log delamination rates versus log G. For all conditions tested, these log–log plots were dominated by linear regions (commonly referred to as Region II) that follow the Paris law. In this region, it was found that bond delamination rates vary dramatically depending on the environment. Furthermore, and unlike with the critical fracture toughness ( G c), the threshold value of G ( G th) for the degraded bond varies from one set of cathodic conditions to another. To model delamination rates as function of the cathodic environment and G, a nonlinear equation capable of modeling subcritical crack growth behavior was used. The experimental delamination data was fitted to this equation in order to determine the coefficients of this equation. For each environment tested, one equation was determined and which describes the bond delamination rate versus G behavior over the entire G-range. Consequently, these coefficients were consolidated into master, easy-to-use, empirical equations that relate delamination rates to G. The resulting empirical model is applicable over a wide range of cathodic conditions of voltage and temperature.