Strain gauges debonding fault detection for structural health monitoring

Physical redundancy is a common approach in applications with safety-critical systems. But that is not always possible in some structural health monitoring (SHM) applications whether for economic, spatial, or safety reasons. Many SHM sensor validating applications only rely on analytical redundancy. In such circumstances, sensor faults and structural damage need to be assuredly discriminated. A self-diagnosis strain sensor operating in a continuous online SHM scenario is considered. The sensor is based on a full electric resistance strain gauge Wheatstone bridge. The state of the art shows that such a sensor has not yet been developed. The loop current step response (LCSR) is a well-known method to detect strain gauge debonding. However, applying the LCSR method to a full strain gauge Wheatstone bridge has some limitations analyzed in this paper. Two new methods for detecting strain gauge debonding are proposed and evaluated. These methods are based on consistency checking of the strain gauges grids temperature measurements—employing an array of (a) digital contact temperature sensors or (b) quasi-contact microelectromechanical system thermopile sensors. The experimental results reveal that both methods are suitable for application in an SHM self-diagnosis sensor scenario. However, the quasi-contact measuring method showed to be more sensitive to the strain gauge grid debonding fault though.