Strain based FBG sensor for real-time corrosion rate monitoring in pre-stressed structures

A strain based corrosion sensor for the detection of environmental corrosion of pre-stressed structures was developed and tested on mild steel specimens readily available. Theoretically, a beam shaped specimen under a displacement load exhibits a linear relationship between the strain observed at any point through the thickness of the beam cross-section. This property was exploited to detect thickness changes in pre-stressed mild steel specimens in a double bending configuration under an electrochemically excited corrosion reaction. The reaction was accelerated by supplying a DC current to the cell where the specimens act as anodes of the system, while graphite rods serve as cathodes. The strain was logged using fiber optic Bragg grating technology and conventional electrical strain gages simultaneously. Results show a strong relationship between the corrosion rate observed by back-calculation from supplied current and the time derivative of the measured strain values. Application of this sensor can therefore be extended to a variety of structures under mechanical loading, proving valuable for both its ability to measure corrosion rate in real-time, while maintaining an intrinsically safe nature appropriate by industrial standards.