## 1 Introduction  
The split Hopkinson bar [1] has been widely used for extracting material properties such as the parameters of strain rate-dependent constitutive models [2; 3] which, in turn, are used for the simulation of high strain-rate events such as high-speed transportation crashes, high-speed machining, rock/building blasts, blast impacts, earthquake impacts, ricochets and penetrations [4; 5; 6; 7], and explosions. While the original inception of the split Hopkinson bar was based on the compressive mode [1; 8; 9; 10; 11], modifications have been made thereafter, including the split Hopkinson tension bar (SHTB). The SHTB measures the stress-strain and strain rate-strain curves of versatile materials at strain rates of approximately 400-2000 s\({}^{-1}\). The specimen materials include metals, soft materials such as foams and elastomers, and civil engineering materials [12; 13] such as cement-based composites, rocks, and (reinforced) concrete. To obtain the tensile pulse in the SHTB, the technique using a hollow cylinder and flange is probably the most widely employed [14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45]. The schematic of the SHTB system that employs a hollow cylinder and flange is shown in Figure 1.  
Briefly, the operation principle of the SHTB is sketched in Figure 1; the hollow striker impacts the flange at velocities of approximately 10-30 m/s. Although the detailed stress transfer mechanism is unknown (revealing the mechanism is the object of this study), it is generally believed that the impact-generated compressive stress wave reflects at the rear (left) end of the flange structure to a tensile stress wave. The reflected tensile wave then travels backwards through the flange structure and enters the incident bar. When this tensile stress wave (\(\varepsilon_{\mathrm{I}}\); incident wave) reaches the right end of the incident bar, where the specimen is attached, a part of the tensile stress wave is reflected back to the incident bar as a compressive wave (\(\varepsilon_{\mathrm{R}}\)), while the rest of it passes through the specimen to enter the transmitted bar as a tensile wave (\(\varepsilon_{\mathrm{T}}\)). The transmitted stress wave (\(\varepsilon_{\mathrm{T}}\)) is measured using a strain gauge, from which the nominal stress of the specimen (\(\sigma\)) is obtained using Equation (1). The nominal strain rate (\(\dot{\epsilon}\)) and strain (\(\varepsilon\)) of the specimen can be obtained most accurately from images of the deforming specimen obtained using an ultra-high speed camera and based on the digital image correlation method. Provided that the designs of specimen geometry, gripping method, and tensile pulse shape are calibrated, the strain  
Figure 1: Schematic of: (**a**) hollow striker, flange, and incident bar (\(L_{\mathrm{f}}\): flange length, \(H_{\mathrm{f}}\): flange height, \(T_{\mathrm{s}}\): striker thickness, \(L_{\mathrm{s}}\): striker length, \(D_{\mathrm{b}}\): bar diameter, and \(V\): impact velocity) and (**b**) the overall SHTB system, where \(\varepsilon_{\mathrm{I}}\), \(\varepsilon_{\mathrm{R}}\), and \(\varepsilon_{\mathrm{T}}\) denote the incident, reflected, and transmitted pulses, respectively, with time (\(t\)). rate (\(\dot{\epsilon}\)) and strain (\(\epsilon\)) of the specimen can be obtained from the reflected strain pulse (\(\epsilon_{\text{R}}\)) measured at the incident bar using the strain gauge; Equations (2) and (3) are used for such purpose.