Experiment on box-section sandwich beams in three-point bending

The structural stiffness is explored for box-section beams in three-point bending. Four hollow tubes of various topologies are designed, manufactured and tested. The observed results show that a significant local compliance exists at the centre of the upper tube wall under the loading patch, in addition to the macroscopic bending of the hollow tube. The predicted and measured stiffnesses are in good agreement for a hollow tube with monolithic walls, and a hollow tube with foam-cored sandwich walls. However, the predicted stiffnesses are much greater than the measured values for two hollow tubes with sandwich walls comprising lattice corrugated cores. This can be ascribed to the imperfections introduced by the manufacturing route either by welding or adhesive bonding, and to the local yielding and large plastic deformations of the upper tube walls under the loading patch.