A novel efficient energy absorber with necking-expansion of foam sandwich tubes

Foam sandwich tube is composed of two tubes and a lightweight foam core possessing various advantages, i.e. low density, excellent mitigation performance and energy absorption, etc. With the hope of enhancing the load bearing and energy absorption capacity of energy absorbers, a novel efficient energy absorber composing of axial necking-expansion deformation mode for sandwich circular tube with metal foam core (SCMF-Tube) by an inner-outer conical-cylindrical die is proposed. Considering deformation modes including necking, stretching, bending and strain hardening of metal tubes as well as densification of the metal foam core, we established an analytical model of necking-expansion deformation for the SCMF-Tube. Then, FE simulations are conducted. Analytical deformation modes, load-displacement curves and bending radii all agree well with the FE results. Effects of material property and geometry on the necking-expansion deformation of SCMF-Tubes are discussed in detail based on the validated analytical model. Adjusting parameters, such as the wall thickness ratio of the inner tube to the outer tube and the maximum diameter of the die can improve the load bearing and energy absorption capacity of the novel energy absorber. Finally, the specific energy absorption (SEA) of the SCMF-Tube under necking-expansion deformation is 68% higher than that of the circular metal tube under expansion deformation.