# Delamination Localization in Multilayered CFRP Panel Based on Reconstruction of Guided Wave Modes
## 5 Conclusions  
In this article, an effective GW inspection setup was proposed to locate the delamination in the multilayered CFRP material. This method has the advantage of locating the delamination either in between the excitation and receiver positions or even between the receiver and the boundary of the sample. The guided waves are excited with a single excitation source, and several receiver positions are used to locate the delamination in the longitudinal direction. Thus, the proposed inspection setup has the advantage of locating the delamination with the minimum number of sensors.  
The A\({}_{0}\) mode was selected for the inspection by analyzing dispersion curves and frequency tuning curves. GW mode selection based on dispersion curves provides only the velocity of a particular mode at different frequencies. Therefore, the selection of GW modes  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Case**} & \multirow{2}{*}{**Receiver**} & \multicolumn{2}{c}{**Distance from**} & \multirow{2}{*}{**Propagation**} & \multirow{2}{*}{**Tof (dt) (\(\mu\)s)**} & \multicolumn{2}{c}{**Estimated**} & \multirow{2}{*}{**Absolute Error**} \\  & & **Delamination to** & & **Time \(t_{2}-t_{1}\) (\(\mu\)s)** & & **Distance (mm)** & \\ \hline
2-1 & R1 & 10 & \(136-125.8\) & 10.2 & 11 & 0.8 \\
2-2 & R2 & 20 & \(142.1-128\) & 14.1 & 15.3 & 4.7 \\
2-3 & R3 & 30 & \(151.3-130.2\) & 21.1 & 22.9 & 7.1 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Localization of delamination when the delamination is between excitation and receiver.  
Figure 18: GW signal received in the case when delamination is between the excitation source and the receiver.  
following dispersion curves is not accurate and is limited. The use of frequency tuning curves has the advantage of selecting dominant modes and optimal frequencies for the inspection. Thus, the A\({}_{0}\) mode was selected for the inspection because it has a dominant amplitude compared to the S\({}_{0}\) mode and is sensitive to a delamination-type defect.  
Phase velocity is one of the important features in detecting and locating the delamination. Phase velocity estimation of GW modes in composite materials with unknown properties is difficult. For this reason, a phase spectrum approach was developed to estimate the phase velocity of GW modes. The estimated phase velocity of the A\({}_{0}\) mode is further used in the developed analytical model.  
The excited GW is reflected, converted, and overlapped with other modes when it encounters delamination. Analysis of GW modes in the presence of low amplitude, converted, and overlapped modes is difficult. For this reason, a novel analytical model was developed to locate the delamination in the presence of low amplitude and overlapped modes.  
The analytical model developed was verified with five different scenarios using numerical and experimental investigations. In the case of numerical results, the delamination position was estimated with an average absolute error of 2.8 mm from the actual position of delamination. In the case of experimental results, the delamination position was estimated with an average absolute error of 2.6 mm from the actual position of delamination.  
Conceptualization, M.R.P., E.J. and V.S.; methodology, M.R.P.; software, M.R.P., V.S. and L.M.; validation, E.J., V.S., L.M. and P.G.; formal analysis, M.R.P. and E.J.; investigation, M.R.P.; data curation, M.R.P. and E.J.; writing--original draft preparation, M.R.P.; writing--review and editing, E.J., V.S., L.M. and P.G.; visualization, M.R.P.; supervision, E.J.; project administration, E.J. and P.G.; funding acquisition, E.J. and P.G. All authors have read and agreed to the published version of the manuscript.  
This research has received funding from the Research Council of Lithuania (LMTLT), agreement No S-MIP-23-122, and is based upon work from COST Action 18203--Optimized Design for Inspection (ODIN), supported by COST (European Cooperation in Science and Technology).  
Not applicable.  
The authors declare no conflict of interest.