A critical evaluation of mechanical models for sandwich beams

Daniele Tonelli, Lorenzo Bardella, and Michele Minelli

DICATA, University of Brescia, Via Branze 43, Brescia 25123, Italy


We focus on the description of the stress state of sandwich beams under bending and shear, a non-trivial task if Saint-Venant's principle does not hold, as it is the case if the skins are somewhat stiffer than the core. Each of the analytical structural models available in the literature turns out to be accurate for a limited range of relative stiffness between core and skins, or sandwich heterogeneity. For a simply supported sandwich beam subject to uniform transversal load, we evaluate the stress by means of (i) the classical theory relying on the linear cross-section kinematics, appropriate if Saint-Venant's principle holds, (ii) the structural theory based on the zig-zag warping (e.g., Krajcinovic, D., 1972, J. Appl. Mech.-T ASME, 39(3):773-787), and (iii) the higher-order theory of Frostig et al. (Frostig, Y., Baruch, M., Vilnay, O., and Shelnman, I., 1992, J. Eng. Mech.-T ASCE, 118(5):1026-1043), the latter usually appropriate when the core is much softer than the skins. The results are compared, for several combinations of material and geometrical parameters, with those of finite element simulations in which the sandwich is modelled as a plane stress continuum. This comparison allows us to provide some graphs which can help in selecting the model appropriate for each sandwich heterogeneity. This is accomplished in terms of non-dimensional material and geometrical parameters the sandwich heterogeneity depends on. We identify and discuss two levels of heterogeneity at which one should switch analytical model, one level being related to the validity of Saint-Venant's principle, the other level concerned with the definition of antiplane sandwich.

Author Keywords: Sandwich structures; Warping; Saint-Venant's principle; First-Order Shear Deformation theory; Higher-Order Shear Deformation models; Antiplane sandwich; Stress analysis; Finite element method