PSI - Issue 47

Ezio Cadoni et al. / Procedia Structural Integrity 47 (2023) 268–273 Author name / Structural Integrity Procedia 00 (2023) 000–000

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Fig. 2. Experimental set-up - Split Hopkinson Tensile Bar: 1. Hydraulic actuator; 2. Pretensioned bar; 3. Blocking system; 4. Input bar; 5. Strain gauges input; 6. Cooling system; 7. Specimen; 8. Strain gauges output; 9. Output bar; 10. Fast camera; 11. Eating system; 12. Recorder system.

Laboratory of the University of Applied Sciences and Arts of Southern Switzerland (Mendrisio) as shown in Fig. 2. It consists of two straight, circular bars with diameters of 10mm and lengths of 9 and 6m . Part of the longer bar (6 m) is used as a pretensioned bar, while the rest (3 m) is used as an input bar. A second bar serves as an output bar. Tungsten alloy specimens are screwed into the input and output bars. By pulling the hydraulic jack, placed at the bar end, the pretensioned bar can store elastic energy and regulate test velocity in relation to load amplitude. Input and output bars are equipped with semiconductor strain gauges to measure strain caused by incident ( I ), reflected ( R ) and transmitted ( T ) pulses acting on the specimen. Engineering values of stress (1), strain (2) and strain-rate (3) are obtained in function of time using one-dimensional elastic stress wave propagation theory: σ eng . ( t ) = E 0 · A 0 A · T ( t ) (1) eng . ( t ) = − 2 C 0 L t 0 R ( t ) (2) ˙ eng . ( t ) = − 2 C 0 L · R ( t ) (3) Ambrell 2.4 kW compact EASYHEAT induction water-cooled heaters were used for the tests at elevated tempera ture [Cadoni and Forni (2019); Cadoni et al. (2022)]. Using this non-contact induction heating, it is possible to supply power precisely to the gauge-length of the specimen, with a power control resolution of 25 W. Specimens were heated at a constant rate of about 3 °C / s to the set temperatures (800 ◦ C- 1100 ◦ C). Three target high strain rates were set at 850 s − 1 , 1400s − 1 and2200s − 1 obtained by imposing, at room temperature, a preloading of 26 kN, 35 kN and 50 kN, respectively. An HBM-Gen2 data acquisition system was used to collect strain gauge signals, while a fast camera was used to record the specimens’ failure at 43kfps at high speed. Tungsten alloys are known for their high melting point, high density, and excellent mechanical properties, mak ing them attractive materials for various applications, including high-temperature environments and high strain rate loading conditions. However, the influence of high temperature on tungsten alloy behaviour under high strain rate loading, particularly in tensile testing, is not well understood. One of the main challenges in studying the influence of high temperature on tungsten alloy behaviour under high strain rate loading is the lack of experimental data. This is because it is di ffi cult to generate the necessary high strain rate loading conditions at high temperatures. Further researches are needed to better understand the e ff ect of temperature on the mechanical properties and microstructure 4. E ff ect of high strain-rate and elevated temperature on direct tensile test