Composite sandwich structures often have complicated geometry that limits optical access, which prevents deployment of full field imaging techniques, such as Digital Imaging Correlation (DIC) and Thermoelastic Stress Analysis (TSA). During testing, it is difficult to use traditional inspection approaches to internal regions where debonds may occur in the interfaces between the face sheets and core material. Here, mirrors are utilised to allow optical access to face sheets of sandwich specimens loaded in bending, so that TSA can be employed to characterise interfacial debonding through the face sheets. To separate the surface thermoelastic response, ΔT, from that generated from the interfacial regions, DIC is used to obtain the surface strains. From this, ΔT from the surface in the vicinity of a debond is estimated. The interface ΔT is then obtained by subtracting it from ΔT obtained from TSA. From this, the interfacial fracture process can be characterised
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