Studies on the Prediction of Elastomer-to-Steel Adhesive Bond Life in Cathodic Environments

In this paper, we present a summary of the research done to date on modeling the debonding of elastomer-to-steel adhesive bonds under cathodic conditions. In the Introduction Section, we address some of the peculiarities of the two documented debonding modes: weakening and delamination. In the following sections, we first discuss the accelerated durability data collected (some under highly accelerated conditions) using a primer/adhesive system specially formulated for bonding elastomers to metals. For enhanced durability, this control system was also modified by incorporating γ-aminopropyltriethoxysilane (γ-APS). This modification resulted in improved resistance to the alkali as evidenced by decreased mass uptake of free-standing, neat primer films. Also, cathodic durability results of adhesively bonded joints show a decrease in delamination rates for the silane-modified bonds as compared to the control system. Having collected a significant amount of cathodic durability data (for both loaded and unloaded adhesive bonds), we set on developing mathematical models that are capable of predicting the life of these bonds under cathodic conditions. A semi-empirical model that simulates the weakening (unloaded) mode of bond debonding (both weakening rates and the characteristic delay time) under various cathodic conditions is first reviewed. Then and for simulating the delamination (loaded) mode of cathodic debonding, we address two models: one empirical and one semi-empirical. The latter model utilizes some of the physical principles underlying the delamination phenomenon. Both of these models offer mathematical equations which relate cathodic debonding rates of elastomer-to-steel bonds to environmental parameters as well as G, the applied strain energy release rate. These models may serve as predictors of service life for similar elastomer-to-steel adhesive bonds in cathodic environments.