Destructive vs. non-destructive methods for the mechanical characterisation of tannin-based thermoset foams

The mechanical properties of a broad range of thermoset foams based on tannin were investigated through destructive compression tests, either with or without rigid plates glued to the opposite faces of the samples, and through a rather new, non-destructive, quasi-static method. The main objective was to compare both techniques, as well as the effect of the presence of plates, and to discuss the relevance of each for properly characterising the materials. Gluing stiff plates to the samples was found to be a key point for the appropriate determination of the elastic modulus of brittle foams, whereas it did not affect that of elastic-plastic foams. In contrast, the compressive strength did not depend on the kind of test. The results obtained by destructive compression were then compared to those of the new non-destructive technique, proving that the latter was suitable for characterising elastic-plastic foams but not brittle foams. However, the new method allowed determining Poisson ratio and loss factor, which had never been measured so far for this kind of materials.