Influence of density on the behavior of sandwich panels

High strength carbon and glass composites are being used to fabricate sandwich panels with high specific strengths. Typically, organic polymers are used as the matrix for binding the fabrics and adhesion to wood. Unfortunately, organic matrices are often flammable and leave structural elements susceptible to rapid damage and collapse in the event of a fire. The results reported in this paper deal with the performance of sandwich panels made using an inorganic polymer matrix. The room-temperature curing resin is called Geopolymer and is resistant up to 1000°C. Using this inorganic matrix, alkali-resistant glass and high strength carbon tows and fabrics were laminated onto oak and lightweight balsa wood cores to obtain rigid and high strength sandwich panels. The primary variables investigated were: the density of wood, the thickness of the wood cores, and the amount and type of reinforcement on the facings. One hundred and thirty beams were tested in flexure to determine the load-deflection response of these sandwich composites. The beams were analyzed as reinforced wood beams using the concepts of composite action and flexure theory for linearly elastic and elastic-plastic materials. The influence of density on flexural strength, stiffness, toughness, and specific strength were also evaluated. Lower density cores provide better performance and exhibited the largest increases in most categories. Flexural theory using linear elastic material behavior provides good prediction in the linear range. However non-linear analysis is needed to predict the strength accurately. As the density reduces, the shear stiffness plays a major role in the failure mechanism.