A recent six degree-of-freedom interactive buckling analysis for sandwich struts is extended from isotropic to orthotropic core materials. The interaction, which involves an overall mode of buckling coupled with local wrinkling predominantly on one face, arises as a progressive destabilization from neutral bifurcation in the overall mode alone to a highly unstable secondary bifurcation in a combination of three independent buckling modes. The analytical model, which allows separately for bending and shear deformations in the core, is illustrated by application to a set of typical sandwich struts. An optimum core orthotropy that maximizes the interaction is found. In combination with the earlier optimum wavelength for local wrinkling, this suggests that secondary destabilization can occur almost immediately after the initial (triggering) bifurcation.
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