Background

Corrosion management concepts utilising the application and integration of predictive tools for corrosion occurrence and growth will be a driver for new technical advances in the field of corrosion maintenance, and in the development of new structural designs, materials and processes for surface protection. Additional benefits can be expected by reduced time-to-market for new products.

Current maintenance philosophy claims that all corrosion damage has to be identified and repaired prior to becoming structurally critical. The consequences are unanticipated and result in unscheduled maintenance with high costs. The total annual direct cost of corrosion, for example to the US aircraft industry, is estimated at $2.2 billion, which includes the cost of design and manufacturing ($0.2 billion), corrosion maintenance ($1.7 billion), and downtime ($0.3 billion). A reliable prediction of the occurrence of corrosion flaws and corrosion propagation would provide the basis for new cost-efficient maintenance and repair strategies.

Objectives

SICOM will develop models that can become an essential part of future predictive maintenance concepts. They will deliver the information about onset and evolution of corrosion and thus fill the gap between corrosion detection or monitoring and the calculation of the structural impact of corrosion. Data from environmental condition or corrosion monitoring systems and non-destructive inspection can be used as input data. Model outputs will be utilised for the repair decision process or can supply structural integrity calculation programmes.

Modelling parameters will be defined, which represent corrosion condition and in-service experience of aircraft. Localised corrosion will be simulated by a numerical microscale model with regard to microstructure and the micro-electrochemical condition. The corrosion rate of aluminium alloys in the meso-scale of occluded cells by means of numerical calculation will be modelled as a function of physical and geometrical factors for a given macro-environment. An engineering-based numerical model for prediction of galvanic corrosion behaviour will be developed and up-scaled for application to structural elements of aircraft. The models are intended to be incorporated into a decision-support tool to enable the engineer to view the data generated by the models but also to examine the trends of the data.

Description of work

A numerical microscale model will simulate localised corrosion of aluminium alloys with regard to microstructure and the micro-electrochemical conditions developed. The corrosion rates of aluminium alloys will be provided in the mesoscale of occluded cells by means of a numerical calculation as a function of physical and geometrical factors for given macro-environments. A numerical model for prediction of galvanic corrosion behaviour will be developed and up-scaled for application to structural elements of aircraft. The influence of surface treatment on modelling results will be included with regard to inhibitor release from protection systems, role of clad layer influence and oxide degrading effects. A decision-support tool will be established for exploitation and implementation of the project results in scientific and technical applications. A further extension of the models is to take into account specific surface treatment of the aluminium alloy and their localised breakdown.

Results

The following major results are expected:

• specification of requirements for in- and output data used in different fields of application;
• mass transport model and the evaluated, critical parameters that trigger localised corrosion;
• numerical calculation of the corrosion rate of aluminium in an occluded cell;
• advanced modified mass transport model for the impact of a clad layer that includes the relevant (complex) geometrical and chemical parameters;
• galvanic corrosion model predicting the corrosion rates for typical structural joints under varying conditions;
• a decision-support software tool will be designed and provided to enable a wide application in corrosion management.