# Thermographic Non-Destructive Evaluation for Natural Fiber-Reinforced Composite Laminates
## 6 Conclusions  
Table 8 shows the capabilities of the thermographic techniques applied on the natural fiber-reinforced polymer composites. Overall, IRT shows clearer results than UT and CW THz. Phase-based PT and LT can provide depth information and clearer results for more features than PCT and VT. VT can only show clearer results for the delamination in BFRP and the impact damage detection in SCB. The flashes modality can provide clearer results than halogen lamps modality, but the latter can detect deep-defects. On the contrary, quantitative analysis for shallow-defects is available in the flashes modality because a higher frequency could be reached. The fiber identification is difficult for BFRP, but feasible for jute/hemp hybrid laminates and SCB. In addition, the delamination was not found in the two vegetable fiber laminates, which may be caused by the different structures compared to BFRP--the mineral fiber composite.  
Figure 14: Phase-based LT for the SCB laminates.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**Type of Materials**} & **BREP** & **Jute/Henp Hybrid Laminates** & **SCB** \\ \hline \multirow{3}{*}{Defect} & Resin-rich & LT (phase) \(>\) PT (phase) \(>\) PT (OCT) \(>\) VT (OCT) & LT (phase) \(>\) PT (phase) \(>\) PT (OCT) & LT (phase) \(>\) PT (phase) \(>\) PT (OCT) \\  & Impact damage & LT (phase) \(>\) PT (phase) \(>\) PT (OCT) \(>\) VT (OCT) & LT (phase) \(>\) PT (phase) \(>\) PT (OCT) \(>\) PT (OCT) & VT (OCT) \(>\) LT (phase) \(>\) PT (phase) \(>\) PT (OCT) \\  & Fiber identification & Unavailable & LT (phase) \(>\) PT (phase) \(>\) PT (OCT) & LT (phase) \(>\) PT (phase) \(>\) PT (OCT) \\  & Delamination & VI (OCT) \(>\) LT (phase) \(>\) PT (phase) \(>\) PT (OCT) & No data & No data \\ \hline \multirow{3}{*}{Depth} & Shallow-defect & PT (phase)\({}^{1}\)\(>\) LT (phase) & PT (phase)\({}^{1}\)\(>\) LT (phase) & PT (phase)\({}^{1}\)\(>\) LT (phase) \\  & Deep-defect & LT (phase) \(>\) PT (phase)\({}^{2}\) & LT (phase) \(>\) PT (phase)\({}^{2}\) & LT (phase) \(>\) PT (phase)\({}^{2}\) \\ \hline \multicolumn{2}{c}{PT (phase): flashes modality; PT (phase)\({}^{2}\); halogen lamps modality.} \\ \hline \hline \end{tabular}
\end{table}
Table 8: Capabilities of different thermographic techniques.  
**Acknowledgments:** The authors would like to acknowledge the financial support provided by the Natural Sciences and Engineering Research Council (NSERC) of Canada and the Canada Research Chair in Multipolar Infrared Vision (MiViM).  
**Author Contributions**: [PERSON] conceived of, designed and performed the experiments, analysed the data and wrote the paper; [PERSON] provided the project and the graphical abstract as well as helped in performing the experiments, [PERSON] and [PERSON] provided the testing specimens; [PERSON]-C. provided the research guidance; [PERSON] and [PERSON] provided the assistance to the research; [PERSON] is the research supervisor; The manuscript was discussed by all the coauthors.  
**Conflicts of Interest**: The authors declare no conflict of interest. The funding sponsors had no role in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript; and in the decision to publish the results.