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Abstract
The deleterious effect of galvanic activity on the durability of rubber-to-metal adhesive bonds is investigated. The generation of hydroxyl ions at the elastomer/metal bondline due to an imposed voltage (current) is shown to be detrimental for cathodically exposed adhesively bonded structures. Bond weakening was found to be caused by alkali attack on the primer-metal oxide interface and was found to be governed by a diffusion-controlled degradation process. The independent accelerating parameters contributing to weakening were identified as temperature and imposed current density. An Arrhenius relationship was shown to model the effect of temperature quite well. For a given electrolyte, the effect of voltage is accounted for through an exponential relationship that relates the voltages to the corresponding current densities. A model that takes advantage of these relationships was developed and was utilized to fit the experimentally collected weakening data. The model accounts for the delay times as well as weakening rates. This model may be used as a first-order durability predictor for similar adhesively bonded systems upon exposure to cathodic environments.