Parametric study on the impact performance of combined tube expansion-axial splitting

The need for impact energy-absorbing modules in the application of structural crashworthiness is essential. Various alternatives of energy absorbing mechanism based on plastic deformation are presented by numerous investigators, since 1970s until recently, with various application, particularly for vehicles. This paper presents on-going research report on the proposed mechanism that combines two effective plastic energy-absorbing mechanisms, i.e., tube inversion and axial splitting. Both mechanisms provide nearly ideal behaviour of flat force versus displacement characteristics but with its subsequent drawbacks. The previous tube inversion mechanism has less stroke efficiency, whilst current axial splitting mechanism has relatively low response force, hence absorbed energy. By combining the two mechanisms, it is hoped to overcome the drawbacks of each mechanism. Early work on the proposed combined mechanisms has been presented elsewhere. Here, further study is reported with the main objective of establishing the relationship between dimension ratios and impact performance of the new mechanism under development. Parametric study is carried out based on finite element analysis with dynamic plasticity capability using ABAQUS general purpose finite element analysis software, for a number of cases. The geometry parameters selected are pipe dimensional ratio D1/t, and die dimensional ratio D2/D1, with the same material used, that is structural pipe steel API 5L. The numerical result is validated using experimental result. The result is presented in the relationship between geometry parameters (D1/t and D2/D1) and impact characteristics, i.e., force-displacement curve, energy absorption, and stroke efficiency. The study also presents precautions on certain geometry parameter combinations that yields unwanted deformation. The proposed mechanism by combining the two existing mechanisms is new with improved performance and has a potential application on high-capacity impact energy absorption such as in railway vehicles.