Peridynamic Multi-Physical Model for Galvanic Corrosion and Fracture

Corrosion is a complex phenomenon which involves multiple disciplines including electrochemistry, thermodynamics and mechanics. Galvanic corrosion is a particular type of corrosion in which two dissimilar metals/alloys are connected electrically and one of them is corroded preferentially (anode), determined by the galvanic series. Galvanic corrosion is also commonly intertwined with other types of corrosion. For example, pitting corrosion can be seen as a localized or micro galvanic corrosion where the pit region serves as the anode and the passive region serves as the cathode. Efficient and accurate prediction of galvanic corrosion can help evaluate its effect on engineering structures and provide insights on how to prevent it.

The peridynamic (PD) corrosion model views the corrosion as damage induced in the solid by dissolution. Consequently, it can capture important changes that happen near the corrosion front (on the solid side) and offer a more complete description of corrosion damage than other corrosion models. However, in current PD corrosion models, local current density on the corrosion front is given as an input. While this works fine for problems in which the corrosion rate is already known, it cannot handle complicated corrosion problems such as galvanic corrosion, in which the corrosion rate is changing with the electrostatic potential distribution in the electrolyte.

In this work, we formulate the PD Laplace’s equations to compute the electrostatic potential distribution over the electrolyte domain and coupled it with the PD corrosion model to obtain a corrosion damage model in which the corrosion rate is determined at every time step and across the domain by the current electric potential distribution. We further couple this model with the mechanical PD formulation to study crack growth induced from damage initiated by galvanic corrosion. These are the main novelties compared with previous corrosion damage models. An autonomous fictitious nodes method which works for arbitrary boundaries is used to enforce local boundary conditions for the PD Laplace’s equations. We verify the model for a 2D case with homogeneous electric flux in the domain by first testing the initial electric flux distribution and then the corrosion depth. Afterwards, we validate the model against experimental results available from the literature for galvanic corrosion between steel and a magnesium alloy. The results for the initial current density distribution and final corrosion profile are also compared with those from a model built using COMSOL. Finally, we solve a coupled corrosion-fracture problem to show the model’s potential in resolving failure caused by the combination of deep and narrow crevices created by galvanic corrosion and crack propagation resulting from compounding mechanical loading.