ON STRESS-CONCENTRATION IN THE BENDING OF SANDWICH BEAMS WITH TRANSVERSELY FLEXIBLE CORE

Stress concentrations in sandwich beams with a 'soft' core subjected to bending loading are investigated and the level of stresses is analytically determined. The cases discussed include stress concentration effects (i) in the vicinity of concentrated loads and supporting zones; (ii) at the edges of debonding regions-edge and inner delamination types at the interface layer between the skins and the core; and in the vicinity of vertical cut-off connections; and (iii) at the location of diaphragms that are bonded and unbonded with the adjacent core and embedded in it. The results are determined with the aid of a variational rigorous, analytical, systematic elastic high-order theory that uses closed form solutions. This theory is applicable to any type of sandwich construction with and without discrete diaphragms (i) to any type of loading, concentrated or distributed; and (ii) to any type of boundary conditions including cases in which at the same section the conditions at the upper skin are different from those at the lower skin. The stress concentration effects are presented in terms of deflections, internal forces and normal stresses (peeling) in the interface layers between the skin and the core. A parametric study is conducted and investigates the level of stresses as a result of (i) the vertical modulus of elasticity of the core; (ii) the delamination length; (iii) the reinforcing diaphragm; in a typical connection; and (iv) the presence of diaphragms, either bonded or unbonded with the adjacent core, at specific locations.