Flexural behaviour of sandwich panels under elevated temperature

The objective of this work was to experimentally determine the flexural behaviour of composite sandwich panels under elevated temperatures from 21°C to 180°C. The new generation sandwich beams were fabricated using top and bottom skins made of two plies of bi-axial glass fibre/resin and an innovative phenol-formaldehyde core. The composite sandwich beams and the skins were subjected to flexure test under 3-point static bending test to determine the strength and the stiffness. The elevated temperature effects were applied using an environment chamber. The peak load, strength and the Young's modulus of each specimen under each temperature was recorded. Prior to this, the skin and the core materials were also subjected to Dynamic Mechanical Analysis (DMA) in order to determine the material properties at elevated temperatures. The glass transition temperatures of the skin and the core were obtained through the DMA as 125.06°C and 136.11°C respectively. A rapid loss in the storage modulus was observed in the core specimens as the temperature increased and the specimens began to decompose beyond the glass transition temperature. The testing of the skin specimens revealed that the storage modulus decreases steadily with the increase in temperature until the glass transition temperature and beyond the transition temperature the storage modulus begins to increase. The flexure test of the skin revealed that the Young's modulus of the specimens decrease steadily with the increase in the temperature before increasing beyond 120°C. The strength of the skin decreases rapidly until 120°C and shows a slight increase in strength beyond this temperature. The flexure test of the sandwich panels revealed that the Young's modulus of the sandwich panels decreases steadily as the temperature increases. The strength of the sandwich panels was found to increase with the increase in temperature until 50°C and starts to decrease beyond this temperature before showing a slight increase in the flexural strength at 180°C. A theoretical equation was developed which predicted the behaviour of the sandwich panels under elevated temperature. The theoretical equation revealed that the Young's Modulus of the sandwich panel predicted through the theoretical equation correlated well with the experimental values until 100°C. From 120°C, the experimental values were lower than the values obtained from the prediction equation due to the partial loss in the composite action of the sandwich panel