Modeling Cathodic Weakening of Rubber/Steel Adhesive Bonds as Liquid-Solid Reactions

In order to predict the loss of adhesion in adhesive bonded joints under cathodic conditions, empirical and semi-empirical approaches were previously implemented by Hamade and coworkers. In this paper, a method is presented to estimate bond weakening progress via numerical simulations after being modeled as a liquid-solid chemical reactor. The diffusion and chemical reaction mechanisms involved in bond weakening are mathematically represented via a simplified, 2 partial differential equations (p.d.e.) boundary value problem (BVP) which is a reduced version of the more complex electrochemical formulation needed to fully describe the chemistry at the bondline under cathodic conditions. The model presented is analytical/empirical hybrid formulation solvable by numerical methods and is made possible by the empirical knowledge developed previously by Hamade and coworkers regarding the dependence of the diffusion and chemical reaction parameters on cathodic conditions. The findings support that weakening is governed by a chemical reaction-controlled mechanism at relatively short distances and by a diffusion-controlled mechanism as the degraded front propagates. The numerical model is validated using experimental weakening data collected previously. The numerical solutions provide estimates of the life of the bonded joint (weakened length vs. time) as function of cathodic parameters. (C) Koninklijke Brill NV, Leiden, 2012