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.