Equivalent constitutive behavior of sandwich cellular cores

The constitutive behavior of a continuum equivalent to cellular core are calculated using detailed finite element models of representative unit cell for hexagonal, square and triangular core shapes. The variation of the constitutive behavior of the homogeneous structure equivalent to the cellular core with respect to the core density is studied. Formulas for direct calculation of the constitutive behavior are generated for cell size range 1/8″ to 3/8″ and core density range 1.0 pcf to 8.1 pcf. The calculated properties are tested using two-dimensional and three-dimensional finite element modeling techniques of sandwich panels. Error analysis is then performed to identify the effect of the panel size to cell size ratio as well as the facesheet thickness to core thickness ratio on the error. Results show linear variation of mechanical properties with core density except for panel-wise in-plane shear modulus which is too low and can be neglected. The facesheet thickness to core thickness ratio was found to have low impact on the error while the panel size to cell size ratio was found to have a significant impact on the error level. A minimum panel size to cell size ratio of 60 was found to be necessary to maintain error within 5%.