A novel Hopkinson tension bar system for testing polymers under intermediate strain rate and large deformation

Abstract

Hopkinson bar technique frequently encounters technical challenges when dealing with large strain requirements, especially under intermediate strain rate tensile loading. In this work, the striker tube of traditional Hopkinson tension bar was specifically modified to allow the incident wave to circulate through the incident bar with little intervals, forming an ultra-long tensile stress wave. And a short transmission bar with one end fixed was specifically designed as transmission bar, to precisely record the derived ultra-long transmitted wave. Finite element analysis was performed to simulate for the sensitivities of loading system, and the results indicated that the length discrepancy between the striker tube and incident bar affects system accuracy. To validate its capability under intermediate strain rate loading, tensile tests were carried out on a modified rubber under average strain rate 80 s⁻¹, with the strain measurements aid from digital image correlation technology. Excitedly, the system was experimentally demonstrated to achieve wave durations up to 150 ms and strain up to 1,200%. Further discussions were also conducted for potential limitations and extensive extensions.