Understanding fretting corrosion to improve the reliability of on-board systems

Towards more durable and robust embedded systems for the automotive, aeronautics and space industries

Mack Mavuni Nzamba, a former PhD student in the Molecular Physics Department (DPM) and currently a researcher at the Université Nouveaux Horizons in Lubumbashi, Democratic Republic of Congo, and Erwann Carvou, a teacher-researcher at the IPR's DPM in charge of the research activity on electrical contacts, have recently published their work on fretting corrosion modelling of electronic connectors in the IEEE Transactions on Components, Packaging and Manufacturing Technology.

Context

Electrical connectors are used to conduct signals or electrical power between the various components of mobility-related on-board systems. Unfortunately, electronic contactors have a tendency to wear out quickly. When subjected to vibrations, these connectors can suffer potentially catastrophic failures in the case of on-board power components. Contactor wear is therefore at the heart of the durability of on-board systems. The underlying mechanism is called fretting corrosion, and is the result of undesirable chemical reactions between materials in contact and their environment. These reactions are caused by moisture, contaminants or other corrosive factors. When fretting corrosion occurs, it can lead to increased electrical resistance in contacts, which can affect electrical conductivity, and even cause complete failure of the electronic device. Today, the optimization of these connectors remains empirical, by means of a trial-and-error approach: an obvious lack of modelling, which would enable us to find an optimal design!

Scientific approach

Mack and Erwann set up simulations on the scale of the connector, with unprecedented resolution! These simulations take into account all the components of a connector and are based on continuum mechanics, whose equations are solved using the finite element method. The simulations enabled Mack and Erwann to determine the contactor's resonance frequencies. In order to observe the contactor's behavior in use, the contactor simulations were repeated at several amplitudes and external loading frequencies. But all good simulations need to be validated, so the numerical model implemented and the resulting simulations were compared with experimental data obtained using a laser vibrometer capable of measuring relative displacements at the point of contact, and scanning electron microscopy (see figure). The simulations enabled to determine the loading amplitude at which fretting corrosion occurs, and therefore at which the electrical resistance of the contact increases. They also showed that, despite wear, corrosion and oxidation do not accumulate on silver connectors.

Figure(left) Comparison between simulations and experimental measurements of relative displacements within the connector and (right) scanning electron microscopy imaging of the contact corrosion mechanism.

 

Project and perspectives

The work carried out by Mack and Erwann is part of a cifre thesis (academic/industrial) collaboration between IPR and Aptiv, co-supervised by Laurent Morin, head of Aptiv's R&D center based in Épernon. Their work has demonstrated the ability of simulations to predict the risk of fretting corrosion in electronic connectors, so their tool could be used to optimize not only their geometry but also their chemical composition, reducing the experimental need for future certification. All in all, a valuable tool for reducing the (ecological) cost of developing more robust connectors.