Thermal and Mechanical Characterisation of Sandwich Core Materials for Climatic Chamber Shells Subjected to High Temperatures

Climatic chamber testing conditions are becoming more demanding. A wide range of temperatures is used to check the quality of products and materials, since they are constantly being improved. However, there is no literature on how the components of the climatic chamber panels react under high temperatures. The present work therefore sets out to perform a thermal and mechanical characterisation of four core materials often used in sandwich panels: balsa wood, mineral wool, and polyethylene terephthalate and polyurethane rigid foams. The thermal characterisation focused on thermal conductivity and the specific heat was characterised using an indirect method developed previously by the authors to simulate a real application scenario where one surface of the sandwich panels was subjected to high temperature, while the opposite surface was kept at room temperature. Steady and unsteady conditions were analysed up to 200 °C. Balsa and mineral wool exhibited a nonlinear increase in thermal conductivity with temperature, and the polymeric foams showed linear behaviour. The specific heat results also increased with temperature, and the relation was nonlinear for all the tested materials except for polyethylene terephthalate, which showed linear behaviour. Higher temperatures had the least effect on the specific heat for balsa wood and mineral wool. The polyethylene terephthalate foams were the most affected by temperature. Temperature variation was tested using the impulse excitation technique. The polymeric foams and balsa wood were studied up to 100 °C and 160 °C, respectively. The elastic modulus decreased with temperature. After 24 h of cooling, the tests were repeated and the elastic modulus had regained or even increased its initial value, for all the materials.