Microstructural failure modes in three-phase glass syntactic foams

Samples of syntactic foam containing hollow glass microspheres of 0.108 and 0.253 g/cm³ tap densities, some with a silane surface treatment, were subjected to different stress states and examined for failure modes. All foams contained the same volume fraction of APO-BMI, a bismaleimide resin binder. The samples were tested in compression and in three-point bend, and mechanical properties were compared between the various foams. Microsphere strength had a strong effect on overall uniaxial compressive strength with interface strength playing a secondary, yet significant role. In three-point bending, the role of the interface was much more critical. Cross sections of the compression test samples were examined by optical microscopy, and fracture surfaces were investigated by scanning electron microscopy.