Stress transfer mechanism of flange in split Hopkinson tension bar

To reveal the stress transfer mechanism of the flange in a split Hopkinson tension bar, explicit finite element analyses of the impact of the hollow striker on the flange were performed across a range of flange lengths. The tensile stress profiles monitored at the strain gauge position of the incident bar are interpreted on a qualitative basis using three types of stress waves: bar (B) waves, flange (F) waves, and a series of reverberation (R_n) waves. When the flange length (L_f) is long (i.e., L_f > L_s, where L_s is the striker length), the B wave and first reverberation wave (R₁) are fully separated in the time axis. When the flange length is intermediate (~D_b < L_f < L_s, where D_b is the bar diameter), the B and F waves are partially superposed; the F wave is delayed, then followed by a series of R_n waves after the superposition period. When the flange length is short (L_f < ~D_b), the B and F waves are practically fully superposed and form a pseudo-one-step pulse, indicating the necessity of a short flange length to achieve a neat tensile pulse. The magnitudes and periods of the monitored pulses are consistent with the analysis result using the one-dimensional impact theory, including a recently formulated equation for impact-induced stress when the areas of the striker and bar are different, equations for the reflection/transmission ratios of a stress wave, and an equation for pulse duration time. This observation verifies the flange length-dependent stress transfer mechanism on a quantitative basis.