Quasi-static and flexural fatigue testing of polyurethane foam core sandwich composites monitored in-situ with the acoustic emission (AE) sensors indicated core shear and tearing to be the predominant failure activities that lead to eventual catastrophic failure. The foam core sandwich composite lifetime underwent substantial reduction as a function of increasing stress level according to the S-N curve. Flexural fatigue endurance was beyond a 500,000 cycle arbitrarily established cutoff below 60% of the ultimate static load. AE analysis was used to classify damage for the various constituents of the sandwich composite. A damage assessment methodology based on changes in cyclic shear modulus and AE analysis is proposed.