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Glass fibre reinforced plastic (GFRP) composites are finding increasing application in aerospace structures. The monitoring of these structures is not only necessary but also mandatory by the safety codes. The present state of the art allows isolation of damage (level II) and the quantification of damage (level III) is the next challenge. The quantification of the damage may allow for better maintenance scheduling and as a result lower downtime for airplanes, yachts and wind turbine which makes it significant in the different disciplines. The paper presents a comparative study of three distinct damage detection methods on a sample of GFRP composite. The aim of the research is to compare the performance of the three methods for the assessment of the deterioration of the composite samples due to the influence of moisture. The electromechanical impedance (EMI) and guided waves (GW) based methods have been shown to be sensitive to moisture induced deterioration. The dynamic strain based damage detection using neutral axis (NA) as a damage sensitive feature is sensitive to moisture induced deterioration as well. In addition to the detection of deterioration, the use of measured strains provides an intuitive way for the quantification of the moisture induced deterioration in the sample. Thus, the present study allows the calibration of the NA based structural health monitoring (SHM) technique using already established SHM methods like EMI and GW based techniques. Hence, it may be seen as a necessary step for the standardization, validation and development of the strain based method for SHM.
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