Abstract: “Sandwich composites with two different thermoset unfilled rigid foam cores (Polyurethane and Polyisocynurate) and different skin to core weight ratios of 1:1 and 2:1 are considered in the present investigation. The foam is considered in sandwich composites because of its light weight structure, easy machining, high stiffness, damping and insulation capabilities. A combined experimental and finite element analysis is used to compare the vibration characteristics of these sandwich composites in a fixed free condition using the impulse hammer technique. Fabrication of the sandwich panels was done with a hand lay-up process and a vacuum bagging film based process. The machined and honed specimen beams were impacted by striking with an impulse hammer at various points. The natural frequencies and mode shapes were obtained at a particular point of impact. Finite element analysis was carried out by means of the ANSYS 14 software for simulating the experimental conditions. Both the experimenta”

Keywords: PUF (Polyurethane foam), PIR (Polyisocynurate), Sandwich composites, Hand lay-up, Vacuum bagging, Glass fabric/epoxy face sheet, Impulse hammer test, Finite Element Methods.