Effect of a thin soft core on the bending behavior of a sandwich with thick CFRP facings

Three-point bending tests in the elastic domain were carried out on sandwich specimens with the facings made of unidirectional T800H/3900-2 laminates, and the core of a soft and thin viscoelastic layer, varying the slenderness ratio. A closed-form formula available in the literature, developed for sandwich beams with thick facings, was used to predict the rigidities in flexure, adopting three different methods for the calculation of the shear rigidity. The best results were obtained by the classical sandwich theory, which provided reasonably good correlation with the experimental results, slightly overestimating the actual values. A finite element model consisting of three layers, made of standard CQUAD4 and CHEXA8 elements for facings and core, respectively, was developed, accurately predicting beam bending behavior. From the numerical results, the inability of classical sandwich theory to correctly estimate the bending rigidity is correlated with the through-the-thickness shear deformation of facings, not accounted for in the analysis.