Buckling and nonlinear response of sandwich panels with a compliant core and temperature-dependent mechanical properties

This paper deals with the buckling response and nonlinear behavior of sandwich panels with soft cores that have temperature-dependent mechanical properties and are subjected to thermally induced deformations and mechanical loads simultaneously. This study investigates the effects of the degradation of properties of the core as a result of rising temperature on the response of the sandwich panel. Analyses are carried out for cases of pure thermal loading, with either uniform or gradient temperature fields through the depth of the panel, as well as for thermal loading acting simultaneously with external mechanical loads. The formulation is based on variational principles along with the high-order sandwich panel approach. It takes into account the flexibility of the core in the vertical direction as well as the dependency of the mechanical core properties of the temperature distribution through the core depth. The stress and deformation fields of the core have been solved analytically, including the case where the temperature-dependent properties attain a complex pattern. The buckling equations are derived using the perturbation technique, yielding a set of nonlinear algebraic equations for the case of a simply-supported panel and a uniform temperature field. The critical temperatures and modes of wrinkling and global buckling are determined numerically for some foam types of core made by Rohacell and Divinycell. The nonlinear response caused by thermally induced deformations is presented for Divinycell foam core with different temperature distributions through the depth of the core. Finally, the nonlinear response caused by the simultaneous action of external mechanical loading and increased temperatures on the compressive or the tensile side of the panel, with a thermal gradient through the core depth, is presented. The interaction between elevated temperatures and mechanical loads changes the response from a linear into an unstable nonlinear one when the degradation of the mechanical properties due to temperature changes is considered and the panel is unrestrained. Moreover, the unstable nonlinear behavior becomes even more severe when the face, loaded in compression, is subjected to elevated temperatures. This study reveals that a reliable, realistic design of a sandwich panel that is subjected to elevated temperature (within working temperature range) and mechanical loads must take into account the degradation of the properties of the core as a result of the thermal field even at working temperature range, especially when cores made of foam are considered.