Theoretical prediction and numerical studies of expanding circular tubes as energy absorbers

•Expanding energy-absorbing structure was investigated.•The theoretical model considering the additional shear was accurate.•Both expansion angle and friction had great influence on energy absorption.•With friction, the inflection point of force curve existed between 10° and 20°.

This work investigated the energy absorption behavior of expansion circular tubes. This kind of energy absorption device dissipates the impact of kinetic energy through plastic deformation and friction. A finite element model (FEM) was established with reference to the size of the coupler, which was used for connecting two vehicles. A special case was designed to validate the accuracy of the FEM. Furthermore, a theoretical prediction model that took into consideration the additional shear deformation and expansion ratio enlargement was compared with the steady compressional force of the experiment and numerical simulation. The theoretical prediction was accurate. Based on this valid FEM, a series of parameter studies was developed. Specifically, a list of conical mandrels with different angles from 5° to 40° was established, and the coefficient of friction varied from 0 to 0.3. Both had great influence on energy absorption. The relationship between the expansion angle and steady compressional force is nonlinear, while the friction coefficient and steady compressional force are linear. With friction, the inflection point of force curve existed between 10° and 20°.