PSI - Issue 13

Ivan Smirnov et al. / Procedia Structural Integrity 13 (2018) 1336–1341 Ivan Smirnov et al. / Structural Integrity Procedia 00 (2018) 000 – 000

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shock loads. Nevertheless, literature examination shows that the dynamic response of NС and UFG materials remains poorly understood (see, for example, Pippan and Hohenwarter, 2016; Garkushin et al., 2010; Skripnyak, 2017). This study presents the results of experimental studies on the mechanical response of UFG pure copper to dynamic loading. The grain refinement was obtained under severe plastic deformation (SPD) by the method of equal-channel angular pressing (ECAP) (Valiev and Langdon, 2006). ECAP can be used to obtain sufficiently bulk billets with homogeneous material properties. The choice of copper is due to the fact that this is a common simple single-phase metal exhibiting good structure repeatability after SPD processing, and the structure of pure copper is well studied for various treatment SPD regimes (Mishra et al. 2007). Dynamic experiments were carried out for the case of uniaxial compression of cylindrical specimens (split Hopkinson pressure bar test) and for the case of impact bending of a beam with a V-shaped notch (Charpy test). The studies were carried out on electro technical pure copper M1 (C11000). The chemical composition: up to 0.001As, 0.001Bi, 0.001Fe, 0.001Ni, 0.04O 2 , 0.001Pb, 0.001S, 0.001Sb, 0.001Sn, 0.001Zn, and Cu+Ag the balance. Four states of the material were considered in the experiments. The first condition (DS) corresponded to the delivery state. The as-received material was produced in the form of cold-rolled hard tempered rods with Ø10 mm (Ural Mining and Metallurgical Company, Russia). The second condition (A) corresponded to the as-received material after annealing at 550 °C for 2 h. Such processing allows a homogeneous and fully recrystallised microstructure to be obtained before processing by ECAP. The third and fourth states were obtained by ECAP. The annealed rods were processed using an ECAP die with an interior channel angle of 120°. The rods were processed through four (4ECAP) or eight (8ECAP) passes using route B C (billet rotation around the longitudinal axis by 90° in the same direction between every pass) at room temperature. The material structure in the delivery state and after eight ECAP passes is shown in Fig. 1. The characteristic parameters of the material with different treatments are given in Table 1. The presented grain sizes were determined by the method of secant lines on the images obtained by SEM. The presented tensile characteristics were obtained by testing samples with working part dimensions of 6×1×20 mm, at room temperature and a strain rate of 0.001 1/s. 2. Materials and experimental procedure 2.1. Materials

Fig. 1. Image of material grains in specimen cross section for the annealed as-received state (a) and for the state after eight ECAP passes (b).

Table 1. Characteristic parameters of copper M1 after different treatments. Structure DS A 4ECAP

8ECAP

Average grain size d [μm] Tensile strength  t ȏ M ƒ Ȑ Tensile yield strength  Ͳ Ǥ 2 ȏ M ƒ Ȑ 284 Total elongation δ [%] 6 45 95 Microhardness HV 323

50 49

0.8 120 389 342

0.7 126 427 354

207

65 38

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