Issue 42

T.V. Tetyakova et alii, Frattura ed Integrità Strutturale, 42 (2017) 303-314; DOI: 10.3221/IGF-ESIS.42.32 308 coefficient of the strain inhomogeneity. For specimens with the width of 12 mm the average value of the b k is around 0.010, and for specimens with the width of 20 mm — 0.011 b k  . Figure 5 : Profiles of the longitudinal strain ( ε yy ), calculated along the flat specimen of Al-Mg alloy at the stage of the yield drop and yield plateau forming 0 u  , mm/min b v , mm/min 0 b b k u v   ε Н , % 0.5 55.2 0.009 1.29 1.0 104.6 0.010 1.20 1.0 97.6 0.010 1.17 5.0 458.5 0.011 1.28 Table 3 : Influence of the crosshead velocity on the Chernov ‒ Lüders band propagation ( 0 12.0 b  mm). 0 u  , mm/min b v , mm/min 0 b b k u v   ε Н , % 1.0 98.4 0.010 1.21 1.0 92.0 0.011 1.22 5.0 422.9 0.012 1.35 10.0 845.1 0.012 1.36 Table 4 : Influence of the crosshead velocity on the Chernov ‒ Lüder’s band propagation ( 0 20.0 b  mm). Profiles of the longitudinal strain were calculated along the longitudinal direction at the elastoplastic deformation stage and the stage of hardening as well. The numerical the Portevin-Le Chatelier bands were observed and characterize on the surfaces of the specimens during tension tests. Fig. 6 shows results for the specimen of Al-Mg alloy with a width of 20 mm and a length of 100 mm, note that the time gap t  between profiles is 2 seconds. Lines 1 ‒ 10 correspond to the moments of the relative levelling-off of the longitudinal strain on the specimen’s surface. The experimental study of the strain fields during the uniaxial tension of specimens of the Al-Mg alloy revealed the quasi-periodic character of the development of plastic deformations under conditions of discontinuous yielding of the material, which included the alternation of the stages of initiation and propagation of the strain bands. These processes were characterized by a high degree of strain inhomogeneity and the existence of relative leveling-off of strain fields [14, 15].