## 4 Conclusions  
The present paper introduces a delamination detection and localization technique, which was developed based on the numerical simulations results as well as an experimental test conducted in laboratory conditions. The research was carried out focusing on a specific object which is a composite wind turbine blade. The principle of the presented diagnostic method is to statistically examine changes in the first ten bending mode shapes of the research object regarding the localization of damage. The modal parameters in the meaning of the natural vibrations shapes of the tested blade were assessed calculating the fit coefficients. The calculation procedure was used to search local changes in the combination of the forms of the vibrations that could indicate the presence of delamination. The studies were conducted for several variants of damage location. A total of three damage levels in five positions of the blade coating for simulation calculation were taken into account. For experimental validation of the proposed detection method, data from vibration measurements were collected in three different locations. Additionally, for one location scenario, the measurements for three different sizes of damage area were conducted. For both parts of the presented research, the intact state of the blade was also registered and used in the diagnostic process as a reference signal. In the experimental part of studies, the authors used the high-quality equipment dedicated to non-contact, fast and high accuracy of the vibration measurements. The use of Scanning Laser Vibrometry allowed for optimal accuracy of the collected data with a low level of the noise. Furthermore, the laboratory conditions for the testing procedure enabled to identify the capabilities and limitations resulting from the nature of those type of measurement, which would involve the practical application of the proposed method. The major advantages of the method are, respectively, the speed of calculation, no signal pre-processing required, as well as only one initial parameter affecting the final analysis effect, i.e., the size of the sliding window. The main disadvantage of this method is the need to know the condition of an intact blade or its predecessor. One of the main requirements that should be considered when attempting to implement the proposed diagnostic system in practice are the low levels of signal distortion. The adequately good signal-to-noise ratio of measurement data ensures a high level of fault indication while increasing the sensitivity of the method (it is possible to detect smaller faults). Nevertheless, based on the results described in the article, it can be concluded that the diagnostic method based on the analysis of the shapes of natural vibrations in a complex form using statistical tools is effective even with relatively small damage. Moreover, the use of a combination of the presented diagnostic method and a sensor system built into the blade of the wind turbine would allow for the condition monitoring of the object in real-time. Multiple measurements would enable reducing the influence of measurement noise or accidental errors in data on the detection result, and historical measurements could be used as a reference state. Combining the presented method with other more advanced signal processing techniques (e.g., wavelet analysis or AI techniques) will allow not only to determine the exact edge of the defect but perhaps also to predict the speed and direction of defect formation.