Experimental, numerical and analytical investigations into the internal inversion of mild steel tubes under high velocity axial impact using a die

This paper investigates the internal inversion process of mild steel tubes under axial impact analytically, numerically and experimentally using a die. The analytical model which is based on the energy method, is able to predict the shortening length of the tube and the required force for tube inversion considering tube thickness variation. In order to validate the analytical model, some experimental tests are performed on the steel tubes in a gas gun and the required force for tube inversion is obtained using an impact loading measurement system. The tube inversion process is also simulated using the finite element software Abaqus and finally the obtained results are compared with each other. In the present paper, the effect of impact parameters included the projectile mass and velocity, is investigated on deformation mechanism and energy absorption of the tubes in the internal inversion process. The effect of tube thickness and die radius are also studied in the mentioned process. It is observed that in the situation of constant projectile mass, increasing the impact velocity doesn't have a tangible effect on the inversion force and just increases the tube displacement, but if the impact velocity remains constant, increasing the projectile mass causes increase in the inversion force as well as increased tube displacement. It is also concluded that increasing the tube wall thickness increases the inversion force which makes the tube not to be a good absorbent and decreases the tube displacement. Comparing the experimental, analytical and numerical results provides good agreements between them.