Issue 42

T.V. Tetyakova et alii, Frattura ed Integrità Strutturale, 42 (2017) 303-314; DOI: 10.3221/IGF-ESIS.42.32 305 Al Mg Mn Fe Si Others 95.2 3.18 0.38 0.27 0.8 0.17 Table 2 : The chemical composition (weight percent) of the Al-Mg alloy. Testing procedure The mechanical tests in the paper were carried out in the Instron 8850 servo-hydraulic biaxial testing system (100 kN/1000 N·m, 30 Hz) and the Instron 5989 electromechanical testing system (600 kN) at room temperature. The 3-D digital image correlation measurement system Vic-3D was used to observe and characterize the inhomogeneous strain fields due to the Lüders and PLC bands. The Vic-3D was used with the set of two high-resolution cameras (Prosilica, 16 Mp) and the set of the high-speed cameras (Gazelle, 4 Mp). The software of the system is based on the digital image correlation technique. The DIC is a highly effective computer-vision-based technique, which provides estimation of the displacement and strain fields on specimen surface by matching the reference subsets in the undeformed image (before loading) with the target subsets in the deformed images (captured during test). The surface of all specimens was painted with finely sprayed white and black dots to increase the image contrast. The thermographic analysis was used to estimate the temperature fields, that is, the infrared camera Flir SC7700 with a resolution of 640×512 pixels was applied. It is important to notice that the software and hardware synchronization of the testing and measurement equipment was carried out with the DAQ device NI USB-6251. Fig. 2 shows the testing and measuring equipment used in the research. Figure 2 : The Instron 8850 servo-hydraulic biaxial test system ( 1 ) with registration of the strain and temperature fields by using the infrared camera Flir SC7700 ( 2 ) and the 3D-digital image correlation measurement system Vic-3D ( 3 ). As written above, the aim of this study is to estimate the influence of the stress concentrators and the stiffness of the loading system ( LS R ) on the effects of the serrated flow, on the initiation of strain bands of localized plastic deformation. So, three groups of specimens are used in this investigation. The first group includes the standard flat dog-bone specimens, which have a width of 12 and 20 mm; a gauge length of 50, 75 and 100 mm; a thickness of 2 and 3 mm. The second group is a set of flat specimens with stress concentrators: a single center hole with a diameter of 3 and 6 mm (see Fig. 3 (a)); two holes with a diameter of 3 mm (Fig. 3 (b)). Finally, the flat specimens with an additional deformable part