Buckling of sandwich panels with transversely flexible core: Correction of the equivalent single-layer model using thick-faces effect

Abstract

Modeling a periodic structure as a homogeneous continuum allows for an effective structural analysis. This approach represents a sandwich panel as a two-dimensional plate of equivalent stiffness. Known as the equivalent single-layer, the method is used here to analyze bifurcation buckling of three types of sandwich panels with unidirectional stiffeners in the core: truss-core, web-core and corrugated-core panels made of an isotropic material. The transverse shear stiffnesses of these panels can differ by several orders of magnitude, which cause incorrect buckling analysis when using the equivalent single-layer model with the first-order shear deformation theory. Analytical solution of the problem predicts critical buckling loads that feature infinite number of half-waves in the direction perpendicular to the stiffeners. Finite element model also predicts buckling modes that have non-physical, saw-tooth shape with infinite curvature at nodes. However, such unrealistic behavior is not observed when using detailed three-dimensional finite element models. The error in the prediction of the critical buckling load is up to 85% for the cases considered here. The correction of the equivalent single-layer model is proposed by modeling the thick-faces effect to ensure finite curvature. This is performed in the finite element setting by introducing an additional plate with tied deflections to the equivalent single-layer plate. The extra plate is represented with bending and transverse shear stiffness of the face plates. As a result, global buckling is predicted accurately. Guidelines are proposed to identify the sandwich panels where ordinary model is incorrect. Truss-core and web-core sandwich panels need the correction. Corrugated-core panels without a gap between plates in the core have smaller shear orthotropy and do not need the correction. Modeling the thick-faces effect ensures correct results for all cases considered in this study, and thus one should resort to this approach in case of uncertainty whether the ordinary equivalent single-layer model is valid.

Two-scale micropolar plate model for web-core sandwich panels

“…It is important to note that at this stage the presented 2-D micropolar cannot capture higher, local vibration and buckling modes that may appear within a unit cell at higher frequencies and loads than were studied here. For additional free vibration and buckling analyses of web-core panels by classical and 3-D FE models, see also the papers by Jelovica et al (2016) and Jelovica and Romanoff (2018).…”

“…The 2-D micropolar plate results and those by the 3-D FE model are in good agreement, whereas the 2-D ESL-FSDT plate model based on the classical elasticity theory performs poorly near the center of the plate. Two different sets of constitutive parameters are used in the classical case; those from Table B.3 and the quite differently defined parameters used recently by Jelovica and Romanoff (2018). The classical model cannot capture the antisymmetric shear behavior nor the local face bending that occurs near the line load (see Fig.…”

Post-buckling of web-core sandwich plates based on classical continuum mechanics: success and needs for non-classical formulations

“…The decrease is unphysical and can be corrected by incorporation nonclassical continuum mechanics assumptions into our FSDT-ESL model. As shown by Romanoff and Varsta [21], Jelovica and Romanoff [42] by thick-face plates sandwich theory and by Karttunen et al [36] by micropolar theory, the shear deformations of sandwich panels can have only finite wave-lengths, that is, finite n-values. When using thick-faces effect or micropolar solution, physically correct behavior is obtained.…”

Design space for bifurcation buckling of laser-welded web-core sandwich plates as predicted by classical and micropolar plate theories

“…These investigations also show that the strength predictions between different methods are in good agreement when the loading is in the direction of webs. When loading is turned to the weaker direction, problems occur as presented by Jelovica and Romanoff [15] and Karttunen et al [20] in global, but not in local buckling.…”