An efficient interaction formula and a semi-analytical method are developed for calculating the ultimate strength of steel-elastomer sandwich panels under combined in-plane compression and lateral pressure.

By using the Galerkin method and extending the semi-analytical method to clamped sandwich panels, the governing equations of sandwich panels have been solved by the Galerkin method. The material nonlinearity is treated by iteration and a three-dimensional mesh. For the load case of pure lateral pressure, the ultimate strength from the semi-analytical method is similar to that from hinge line theory and finite element analysis (FEA). However, the semi-analytical method requires about as much computation as FEA, and it is therefore not suitable for design.

Finite element modeling and nonlinear analysis are performed to calculate the ultimate strength of sandwich panels under combined load. The results agree with experimental results. This verifies the accuracy of the current finite element model. The verified finite element model is used to obtain the results for a large set of sandwich panels with various dimensions and load combinations. The FEA results for pure lateral pressure load cases are used to derive a correction factor for the hinge line formula. Statistical analysis confirms that the generalized hinge line formula gives accurate values of ultimate strength of sandwich panels under pure lateral pressure.

Except for the pressure-only FEA data points, the other FEA data points are corrected so as not to count the in-plane load carried by the elastomer core. Based on the corrected FEA data points, a general expression is developed for an interaction equation. The resulting equation has a bias of -0.003 and a standard deviation of 0.029. Since the radius of the interaction curve is close to 1, this standard deviation is of the order of 3%, which shows that the ultimate strength given by the equation is very close to the FEA results. The interaction equation is so simple that the ultimate strength of clamped sandwich panels under combined in-plane compression and lateral pressure can be easily calculated.