Development of damage in some polymeric foam-core sandwich beams under bending loading

The damage mechanisms in sandwich plates with polymer foam cores are investigated. There has been a long-standing controversy on what is the weakest element of sandwich plates, the skin-core bonding or the foam core. Under four-point bending of a sandwich plate, we found that in all cases cracks are nucleated inside the polymer foam core as monitored by a high-speed camera. Several separated small cracks develop in the core; then the small cracks are connected and form the main crack that propagates through the core. We complemented the optical recording by the acoustic emission study which provides an additional insight in the fracture process. In addition, the influence of sub-zero temperature of the ultimate load of each material is examined at discrete values of sub-zero temperature. The results revealed that both materials become increasingly brittle with decreasing temperature.