Experimental and numerical study on splitting process of circular steel tube with enhanced crashworthiness performance

The axial splitting of thin-walled tube is usually considered as an efficient deformation mode to dissipate impact energy thanks to its large stroke ratio. However, the low crushing force and the unstable deformation process, such as crack merging and branching, significantly limit its application in crashworthiness design. In this paper, we propose to enhance the deformation stability through introducing initial kerfs on the inner and outer surfaces of the circular steel tube in its axial direction to guide the propagation of cracks during the splitting process, thus we can improve the crushing force via a significant increase in tube wall thickness. To demonstrate the feasibility of the proposed method, quasi-static compressive experiments on single tube (inner radius r = 55 mm, wall thickness t = 5 mm) and doubled tube (consisted of two tubes with wall thickness t = 5 mm) with kerf depth delta = 0.5 mm split by a radiused die are performed, which exhibit stable deformation processes and high steady-state compression forces (103.32 kN for single tube, and 216.44 kN for doubled tube). Then, finite element simulations are conducted to model the tested samples. It is found that the experimentally observed deformation processes are well captured by simulations, and the relative errors of numerical steady-state compression forces in comparison to experimental results are 0.39% (single tube) and 1.90% (doubled tube), respectively. Finally, based on the validated numerical model, the influence of tube and die dimensions on its crashworthiness performance is discussed. It is observed that the axial load significantly depends on kerf depth, crack number, and tube thickness. The curling radius is nearly not affected by kerf depth, but it almost linearly depends on die radius. Moreover, the tube with larger wall thickness has a higher specific energy absorption.