Collapse of truss core sandwich beams in 3-point bending

Sandwich beams, comprising a truss core and either solid or triangulated fa ce-sheets, have been investment cast in an aluminium-silicon alloy and in s ilicon brass. The macroscopic effective stiffness and strength of the trian gulated face-sheets and tetrahedral core are estimated by idealising them a s pin-jointed assemblies; tests show that this approximation is adequate. N ext, the collapse responses of these sandwich beams in 3-point bending are measured. Collapse is by four competing mechanisms: face-yield, face-wrinkl ing, indentation and core shear, with the active collapse mode dependent up on the beam geometry and yield strain of the material. Upper bound expressi ons for the collapse loads are given in terms of the effective properties o f the faces and core of the sandwich beam; these upper bounds are in good a greement with the measured beam response, and are used to construct collaps e mechanism maps with beam geometrical parameters as the axes. The maps are useful for selecting sandwich beams of minimum weight for a given structur al load index. The optimisation reveals that truss core sandwich beams are significantly lighter than the competing concept of sandwich beams with a m etallic foam core. (C) 2001 Elsevier Science Ltd. All rights reserved.