• Akid, Robert
• Jivkov, Ap
• Leiva-Garcia, Rafael
• Fatoba, Olusegun

Abstract

Despite the numerous studies that have been reported in the literature, modelling localised corrosion still presents significant challenges, especially when accounting for the complex processes of metal dissolution, passivation and repassivation, IR drop, mass transport, hydrolysis and salt precipitation, all of which have non-linear behaviour. Added to this challenge is the need to account for the simultaneous interaction between corrosion and applied stress, in the case of this study that of cyclic loading, notably corrosion fatigue. The resulting geometric defects, i.e., pits, can lead to localisation of strain and subsequently facilitate crack initiation. Given the complicated nature of the physical processes involved, a computational approach to modelling the interaction between localised corrosion and stress can prove valuable in the understanding of the damage processes and mechanisms involving pit development and the pit-to-crack transition.Cellular automata (CA) are discrete computational systems in which the evolution of the state of each cell in the modelling space is determined by the current state of the cell and that of its neighbourhood cells. In this study, CA is used to represent the electrochemical component of the damage, i.e. the loss of solid material. In parallel, the deformation of the cellular structure is analysed by the finite element (FE) method. The coupling of the two mechanisms is made by: (1) changing the dissolution kinetics of cells in the CA model subject to local strains determined by FE; and (2) changing the geometry of the cellular structure in the FE model subject to dissolving cells determined by CA. Consecutive execution of the two analyses with sufficiently small cell size provides a good approximation for the interaction between corrosion and deformation effects on the development and localisation of damage. the cumulative mechano-electrochemical damage process is decoupled into corrosion and mechanical components, which will then be modelled using cellular automata (CA) and finite element method (FE) respectively. The former accounts for the process mechanisms involved in localised corrosion while the later evaluates the mechanical response of the material based on the geometry of the resulting localised damage. These models are then coupled in such a way to provide information flow between them. It is anticipated that the findings of this study will help to understand the time-dependent interaction between corrosion and mechanical loading during the pre-crack stages of corrosion fatigue in more details. Specifically, the evolution with time of damage mechanisms, the geometry of localised damage and stress and strain distribution and the dependencies between them shall will be reported.

Topics

• impedance spectroscopy
• corrosion
• crack
• fatigue
• precipitation
• dissolving
• cellular automata