Expansion of circular tubes by rigid tubes as impact energy absorbers: experimental and theoretical investigation

In this study, expansion of deformable tubes by a rigid tube is introduced as a new mechanism of dissipating energy. In this mechanism of dissipating energy, there is a specific clearance between the surfaces of the rigid and deformable tubes, and the rigid tube is press-fitted onto the top end of the deformable one up to 30 mm. when this arrangement of dissipating energy is subjected to axial compression, the rigid tube is driven into the deformable one; consequently, the impact energy is absorbed by the plastic expansion energy of the deformable tube and the frictional energy at the contact interface between rigid and deformable tubes. Experimental, numerical and analytical study of this process under axially quasi-static loading is presented in this paper. Through the experimental and theoretical studies, major crashworthiness parameters in design are identified. The influence of friction coefficient between the surfaces of deformable and rigid tubes on the value of mean crush load is studied, and typical expansion modes of deformation that may occur during axial compression are characterized. Also, expansion load-displacement history and mechanics of the expansion process as an impact energy absorber are studied. It is shown that this energy absorption method has high crush force efficiency and favourable crashworthiness characteristics both in uniform and non-uniform loading conditions.