Thermal Effects on Composite Sandwich Panels Based on the Extended High-Order Sandwich Panel Theory

Sandwich structures are often subjected to external mechanical loads as well as harsh conditions that may include very low or elevated temperatures, which lead to temperature-induced deformations and possible changes of the mechanical properties of the core, especially when made of polymeric foam. Due to the layered construction and large discrepancy in the material properties of the faces and core, temperature-induced deformations with and without external mechanical loads are in general associated with bending, buckling, and nonlinear response of the sandwich panel with and without degradation of the material properties. This work aims to present a general formulation for sandwich panels subjected to both thermal loads and mechanical loads. It is based on the Extended High-order Sandwich Panel Theory (EHSAPT),  which adopts Euler-Bernoulli assumptions in the thin high stiffness face sheets and a high order displacement field in the thick soft core. In the core, the axial displacement is represented by a third order polynomial and the transverse displacement is represented by a second order polynomial. In this manner, the EHSAPT is able to account for the core’s axial, transverse, and shear rigidity, and allows for an accurate prediction of the shear stress distribution through the thickness of the core in a wide range of core stiffnesses. The thermally induced deformation is introduced through the constitutive relations. Additionally, temperature-dependent material properties and non-uniform temperature distribution fields are both considered in the formulation.  The EHSAPT-based element that had been developed earlier (Yuan, Kardomateas and Frostig, AIAA J. vol. 53, no. 10, pp. 3006-3015, 2015) is further developed to include the thermal effect and is adopted for the numerical solutions. Several sandwich panels that are subjected to either only thermal loads only or combined thermal and mechanical loads are studied as numerical examples to examine the thermal effects on sandwich panels. Both the deformed shape and stress fields are obtained. As the faces and the core of a sandwich panel are made of distinct materials with different thermal coefficients of expansion, the temperature-induced deformation of a sandwich panel may include both in-plane and out of plane deformations for some boundary conditions, even when the thermal field is uniformly distributed over the sandwich panel. It is very different from a homogeneous solid in which the temperature-induced deformation is only in the in-plane direction. As a consequence, when it comes to stability, the thermal effects on sandwich panels may modify the pre-buckling behavior and further cause instability.

Acknowledgment

The financial support of the Office of Naval Research, Grant N00014-20-1-2605, and the interest and encouragement of the Grant Monitor, Dr. Y.D.S. Rajapakse, is greatefully acknowledged.