## 4 Conclusions  
For the first time in scientific literature, concrete evidence of interfacial debonding on real-size sandwich-insulated panels is tracked by AE and complemented by assessment by DIC. The panels were prepared and cast in an identical way, however they showed intrinsically different early behavior due to the manufacturing disbands (i.e., air pockets), flaws, and defects at the materials' interface. This study proves that the continuous and full-field monitoring of the loading process can detect the premature (as early as at 5% of the ultimate load) detachment of the TRC skin from the core and distinguish this phenomenon from other damage sources that succeed, such as cracking, fiber pull-out, and TRC-textile debonding. Early AE activity is classified as shear-dominated damage (micro-fracture due to friction at the interface) based on RT-IF and RA-AF feature analysis. Out-of-plane displacement mapping can pinpoint the zone, up to 150 mm wide, where local debonding occurs, a result that cannot be obtained based on LVDT or other conventional point-measuring techniques. AE source localization can also localize the internal damaged zones earlier than DIC surface inspection (up to a cycle prior to crack formation); the latter can be a great tool for structural health assessment and prevention actions. From this perspective, this is the first work in the literature that demonstrates a methodology to track damage progress on stratified composite panels with complex fractures. The proposed tools wish to enrich the up-to-date knowledge on insulation panels' premature failure and promote an inspection strategy for the optimal use of materials. This preliminary study should be extended in the future by assessing the efficacy of the proposed methodology for experiments dealing with other types of sandwich-insulated panels--i.e., considering steel  
Figure 7: AE events projected at the bottom plane of the TRC skin. In black are the events detected at 3.5 kN/m\({}^{2}\), and in red in Table 1. A strain map at 4 kN/m\({}^{2}\) is projected as a plot background.  
or fibre-reinforced polymer (FRP) skins or using alternative foam core materials such as mineral wool and aerogel.  
Conceptualization, E.T. and M.D.M.; mechanical tests methodology, M.D.M. and H.I.; DIC setup, M.D.M. and H.I.; DIC analysis, AE setup and analysis, E.T.; investigation, M.D.M., H.I., and E.T.; writing--original draft preparation, E.T.; writing--review and editing, M.D.M., D.G.A., T.T., H.I.; funding acquisition, M.D.M. and T.T. All authors have read and agreed to the published version of the manuscript.  
This research was funded by FWO (Fonds Wetenschappelijk Onderzoek-Vlaanderen), grant number 12J7720N. The research of M.D.M. was funded by Agentschap voor Innovatie en Ondermenen (VLAIO) and CRH Structural Concrete Belgium nv (grant number 150251).  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analysis, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.