Bending of sandwich beams with transversely flexible core

Abstract

The bending behavior of a sandwich beam with a foam core is analytically investigated. The beam consists of upper and lower skins, metallic or composite laminated, and a soft core. The loading pattern consists of concentrated as well as distributed loads exerted at the upper or the lower skin or a combination of the two. The analysis includes the effects of the flexibility of the core in the vertical direction on the overall bending behavior. The main parameters affecting the overall behavior and particularly the peeling and the shear stresses between the skins and the core are studied. ANDWICH beams have been used in various industries for many years. A typical beam consists of two skins made of metal or laminated composite and a core. The core is usually made of honeycomb, metallic or nonmetallic, which is stiff in the vertical direction and flexible in the horizontal one. In recent years, plastic foams are used for cores in sandwich structures. In this case, the effect of the transverse flexibility of the core on the mechanical behavior of the beam should be taken into account. This flexibility affects the transverse bend- ing behavior of the beam and leads to unequal deflections of the upper and lower symmetrical skins (see Fig. 1). Sandwich beams with honeycomb cores were considered by many researchers. Reissner1'2 included the shear strain effect on the bending, but only the average bending behavior of the composite beam is considered. Many researchers3'5 dealt with the analysis of beams with an antiplane core, i.e., a core with shear rigidity only. The Hexcel designer manual6 outlines the design procedures for beams with honeycomb cores only. An antiplane-cor e approach with anisotropic and composite skin appears in Refs. 7-9. Ojalvo10 assumed different deflec- tions to the two skins, but neglected the peeling stresses. Ogorkiewicz and Sayigh11 dealt with a foam core by replacing it with an ordinary beam with equivalent properties. In this paper, the proposed analysis includes the effects of the transverse flexibility of the core and the peeling stresses between the skin face and the core on the overall bending behavior. The analysis is general and applicable to metallic or com- posite laminated identical skins. The behavior is described in terms of the deflections, the peeling, and the shear stresses in the adhesive layers. The effect of the variables that govern the behavior is incorporated through a parametric study. The mathematical formulation and the boundary conditions are discussed. The analytical solution for the various types of loading with different boundary conditions is presented.