_Article_  
Stress Transfer Mechanism of Flange in Split  
Hopkinson Tension Bar  
[PERSON] 1,*\(\copyright\), [PERSON] 2 and [PERSON] 3  
1 Mechanics of Materials and Design Laboratory, Department of Materials Engineering,  
Gangneung-Wonju National University, 7 Jugheon-ghi, Gangneung, Gangwon-do 25457, Korea  
2 Laboratory of Solid Properties, Modelling, and Simulation, Department of Mechanical Design  
and Engineering, Chonnam National University, 50 Daehak-ro, Yeosu, Jeonnam 59626, Korea; [EMAIL_ADDRESS]  
3 Computational Mechanics and Design Laboratory, Department of Mechanical and Automotive Engineering,  
Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Korea; [EMAIL_ADDRESS]  
Correspondence: [EMAIL_ADDRESS]  
Received: 8 October 2020; Accepted: 26 October 2020; Published: 28 October 2020  
**Featured Application: The flange length-dependent stress transfer mechanism revealed in this study may serve as a solid background for the design of the split Hopkinson tension bar with a flange and hollow striker. Investigation of the transfer mechanism also reveals that there exists a case where the superposed magnitude of the flange and bar waves is simply the sum of the respective wave magnitudes, despite the area mismatch of the respective wave medium, and no reverberation occurs as the flange wave enters the bar from flange structure. This interesting phenomenon occurs if the flange wave arrives at the impact plane during the period when the flange and bar waves are generated under the influence of the area mismatch. This phenomenon is observed when the impact and reflection surfaces are close, which may also serve as a basis for interpreting the wave interaction and its result (impact-induced deformation) at regions near the free surface of a three-dimensional protective structure.**  
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\({}_{\rm n}\)) waves. When the flange length (\(L_{\rm f}\)) is long (i.e., \(L_{\rm f}>L_{\rm s}\), where \(L_{\rm s}\) is the striker length), the B wave and first reverberation wave (R\({}_{1}\)) are fully separated in the time axis. When the flange length is intermediate (\(\sim\)\(D_{\rm b}<L_{\rm f}<L_{\rm s}\), where \(D_{\rm b}\) is the bar diameter), the B and F waves are partially superposed; the F wave is delayed, then followed by a series of R\({}_{\rm n}\) waves after the superposition period. When the flange length is short (\(L_{\rm f}<-D_{\rm b}\)), 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 results 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.  
impact; wave interaction; reverberation; reflection; transmission; general impedance