Structural performance of metallic sandwich panels with square honeycomb cores

Metallic sandwich panels with periodic lattice cores exhibit superior strength and blast resistance relative to monolithic plates of equivalent weight. Their implementation into engineering structures requires computationally-efficient analysis and design codes that properly account for the complex deformation modes within such cores. The objective of the present article is to devise and assess a continuum constitutive law and to demonstrate its application to the elastic-plastic response of one particular topology: the square honeycomb. The law is based on Hill's yield criterion for orthotropic materials, modified to account for the effects of mean stress and the associated compressibility upon plastic straining. Parameters characterizing initial yield are obtained from both approximate stress analyses and finite element calculations of unit cells. Finite element calculations are also used to calibrate the hardening. Once calibrated, the law is used to simulate the bending response of various sandwich panels under either simply-supported or clamped end conditions. An assessment of the law is made through comparisons with corresponding finite element calculations in which the core and face elements are fully meshed. Additional assessments are made through experimental measurements on a family of honeycomb core sandwich panels fabricated from a ductile stainless steel. Comparisons are made on the basis of the global load-displacement response as well as the distribution of shear strain within the core. Issues associated with end-effects, boundary conditions and deformation localization are addressed. Overall, the comparisons reveal that the proposed constitutive law is capable of predicting most of the pertinent features of honeycomb sandwich panels with high fidelity. Some limitations and potential refinements are described.