Design guidelines for the striker and transfer flange of a split Hopkinson tension bar and the origin of spurious waves

Abstract

Characteristics of the stress pulse generated by impact of a hollow striker on the flange of a split Hopkinson tension bar are investigated via an explicit finite element analysis. Design guidelines are extracted for the hollow striker and flange from the viewpoint of eliminating spurious waves located between the incident and reflected pulses. According to design guidelines, it is desirable to have a striker cross-sectional area the same as that of the flange. It is also desirable to make the cross-sectional area of the striker (flange) the same as that of the bar. As for the flange length, it is recommended to be comparable to the diameter of the bar. The magnitude and duration of the primary stress pulse are consistent with the results of a one-dimensional analysis even when spurious waves are present; meanwhile, overly long spurious waves should be avoided to eliminate their superposition with the reflected pulse. Spurious waves appear when general impedance of the striker is higher than the bar. The origin of spurious waves is a series of step-wise residual pulses generated by multiple cycles of striker impact that make the striker keep compressing the flange after the first cycle of impact. Step-wise residual pulses appear in two forms (continuous waves and discrete waves) in spurious waves due to the secondary impacts during the entrance process of step-wise residual pulses to the flange. The consequences of spurious waves in the use of split Hopkinson tension bars are discussed.