A Novel Linear Polarization Resistance Corrosion Sensing Methodology for Aircraft Structure

A direct method of measuring corrosion on a structure using a micro-linear polarization resistance LPR sensor is presented. The new three-electrode LPR sensor design presented in this paper improves on existing LPR sensor technology by using the structure as part of the sensor system, allowing the sensor electrodes to be made from a corrosion resistant or inert metal. This is in contrast to a two electrode LPR sensor where the electrodes are made from the same material as the structure. A controlled experiment,conducted using an ASTM B117 salt fog, demonstrated the three-electrode LPR sensors have a longer lifetime and better performance when compared to the two-electrode LPR sensors. Following this evaluation, a controlled experiment using the ASTM G85 Annex 5 standard was performed to evaluate the accuracy and precision of the three-electrode LPR sensor when placed between lap joint specimens made from AA7075-T6. The corrosion computed from the LPR sensors agreed with the coupon mass loss to within a 95confidence interval. Following the experiment, the surface morphology of each lap joint was determined using laser microscopy and stylus-based profilometry to obtain local and global surface images of the test panels. Image processing, feature extraction, and selection tools were then employed to identify the corrosion mechanism e.g. pitting, intergranular.