Issue 42

T.V. Tetyakova et alii, Frattura ed Integrità Strutturale, 42 (2017) 303-314; DOI: 10.3221/IGF-ESIS.42.32 307 R ESULTS AND DISCUSSIONS Experimental strain fields analysis during the uniaxial tension of the flat dog-bone specimens his section describes some results on experimental investigation of the spatial-time inhomogeneity due to the Chernov-Lüders behavior during uniaxial tension of flat dog-bone specimens. The longitudinal strain, the local strain rate and temperature fields were analyzed on the specimens’ surfaces according with the stress-strain curves. Fig. 4 shows the ‘σ–ε’ curve and the evolution of local strain rate observed on the surface of the carbon steel specimen ( 0 100 l  mm, 0 20 b  mm, 0 3 h  mm), at the nominal strain rate of 3 1.67 10   s ‒ 1 . It is important, that the stage of the yield drop and the yield plateau forming was under observation, that is, the time range was from 1 t to 9 t (see Fig. 4). At the initial stage the deformation of the material was running uniformly up to the upper yield point, or the yield drop. The initiation of the Chernov- Lüders band caused the rapid jump of the longitudinal strain level registered on the specimen surface from the grip side at moment of transition from the yield drop to the yield plateau, or the lower yield point. At the same time, the load value declined. When the strain band reached the opposite side of the specimen, the configuration of the longitudinal strain fields became almost homogeneous. It is important to note that in the region where the front of the localized strain had passed, the material’s deformation processes stopped until the next deformation stage — the material hardening stage. More details can be found in [13]. Figure 4 : Evolution of local strain rate showing the propagation the Chernov-Lüders bands on the specimen surface during a tension test ( 1 9 t t t   ). The flat dog-bone specimens (Al-Mg alloy) with a width of 12 mm and 20 mm; a gauge length of 50, 75 and 100 mm were tested at the nominal strain rate of 4 1.67 10   s ‒ 1 . Fig. 5 depicts the set of profiles calculated along the gauge length of the specimen with a width of 10 mm, a length 75 mm and a thickness of 3 mm based on the analysis of the strain fields. A time gap between profiles is constant and equals 2.0 t   s. The direction of the Chernov-Lüders band propagation is marked with the arrow ( b v ). The average value of the longitudinal strain ( ε Н ) achieved after the strain band propagation (line 1 , Fig. 5) was around ε 1.26 Н  %. To estimate the influence of the strain rate and specimen geometry (width, length) on the Chernov- Lüders behavior, mechanical tests were carried out with different crosshead velocities ranging from 0.5 mm/min to 10 mm/min. A brief summary of the mechanical tests carried out in the present study described in Table 3 and Table 4, where b k — a T