Experimental study of the compression behaviour of syntactic foams by in situ X-ray tomography

Syntactic foams (hollow glass microspheres embedded in a polymeric matrix) are being used increasingly for thermal insulation purpose in ultra-deep water. A better understanding of the damage mechanisms of these materials under such a hydrostatic loading condition would be useful in determining actual material limits, improving phenomenological modeling and developing novel formulations in the future. To achieve this goal, a study based on X-ray microtomography was performed on various syntactic foam materials (epoxy/PP/PU matrix). Spatial resolution of (0.7 μm)3 and in situ non-destructive scanning allowed unique qualitative and quantitative analysis of the composite microstructure during stepwise confined compression testing in the dry state. It is shown that in the three materials, the thickness of the spheres is rather constant while their diameter is strongly distributed. The adherence is strong between PU and glass and rather weak between both PP and epoxy and glass. In the two foams where the matrix is more compliant (PU and PP), damage is homogeneously distributed and affects mainly the larger spheres, while in the stiff and strong epoxy material, damage is localized in bands.