Experimental Application of a Reversible Reference Damage Model for Radar-Based SHM of Glass Fiber Reinforced Polymer Structures

Ultra-wideband electromagnetic waves are used in many applications of structural health monitoring (SHM). The inspection of large glass fiber composite structures poses a significant challenge and requires additional research and development to guarantee a safe and reliable operation. SHM based on a permanent sensor installation and combined with advanced data analysis approaches can help to ensure structural integrity. Therefore, a widely used approach is to evaluate the structural condition by comparing measurements from the healthy state with the current state of the structure. In this work, a novel reversible reference damage model for a delamination is presented that can be detected with a frequency modulated continuous wave (FMCW) radar at 60 GHz. The reversible scatterer is a sandwich model made of Rohacell<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> material and erosion protection tape specially developed for field application in wind turbine blades (WTB). The reference damage model was successfully tested numerically and experimentally in preliminary investigations. A damage indicator (DI), represented by the root mean square deviation (RMSD) of two structural states, i.e. healthy and damaged, is calculated to detect a reference damage in a WTB segment.