A novel linear polarization resistance corrosion sensing methodology for aircraft structure

Abstract

A direct method of measuring corrosion on a structure using a micro-linear polarization resistance (ìLPR) sensor is presented. The new three-electrode ìLPR 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 twoelectrode ìLPR 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 ìLPR sensors have a longer lifetime and better performance when compared to the two-electrode ìLPR 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 ìLPR sensor when placed between lap joint specimens made from AA7075-T6. The corrosion computed from the ìLPR sensors agreed with the coupon mass loss to within a 95% confidence 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).