Thermomechanical behavior of sandwich panels with graphitic-foam cores

Structural sandwich panels with graphitic-foam cores are considered for applications where extraordinary thermal conductivity of the core material may offer unique benefits for challenging thermoelastic structures. Sandwich panels constructed with carbon-fiber facesheets and graphitic-foam cores could provide a viable solution for “optical benches,” which require high stiffness and thermal stability; such panels should exhibit lower susceptibility to thermal distortion than sandwich panels constructed with traditional honeycomb cores or monolithic plates of materials having low thermal conductivity. Specimens of sandwich panels were fabricated with graphitic-foam cores, aluminum facesheets and carbon-fiber facesheets, as well as with honeycomb cores for the purpose of comparing behaviors. Measurements of plate bending behavior and through-thickness thermal conductivity were performed with these specimens; resulting data were used to validate analytical models. Separate testing was conducted to measure the shear modulus of graphitic foam in simple shear, as that strongly influences the bending behavior of sandwich panels, and has not appeared previously in the published literature. Out-of-plane distortion of sandwich panels subjected to asymmetric thermal loading was measured using an optical surface profilometer. Results of these measurements demonstrate that the use of graphitic foam as core material in sandwich panels greatly reduces their tendency to experience thermal distortion.