Issue 27

T.V. Tretiakova et alii, Frattura ed Integrità Strutturale, 27 (2014) 83-97; DOI: 10.3221/IGF-ESIS.27.10 85 Designation L l B b a r Size, mm 120.0 50.0 22.0 12.0 2.0 5.0 Table 1 : The geometrical parameters of the flat dog-bone specimens of Al-Mg alloy for tests on uniaxial tension. The registration of strain fields’ evolution was conducted by the non-contact 3-D digital image correlation measurement system Vic-3D with the recording rate of 15 images per second and DCP cameras resolution of 4.0 Mp. It is the multi- camera system which can be used for problem solving of deformable solid mechanics: experimental investigation of non- uniform strain fields and analysis of failure conditions in bodies with concentrators of different geometry, research of inelastic material deformation processes in complex strain-stress conditions, study of displacement and strain fields propagation during crack initiation, damage accumulation and material failure, etc. Figure 2 : Experimental setup for uniaxial tension of Al-Mg specimens. The procedure of the uniaxial tension loading experiment with the measuring of surface deformations includes several steps: preparation of specimen’s surfaces by coating with white and black spray paint to generate random pattern; attaching the specimen to the hydraulic fixtures with flat specimen platens; calibration of the stereovision system with the set of target grids; synchronization of the imaging and loading data by using the image acquisition system Vic-Snap and a data collector. All analyses were performed by the software Vic-3D with a subset size of 19×19 pixels 2 and with a step size of 4 pixels between subset centers. Data extraction through image analysis was carried out by using the NSSD criterion (normalized sum of squared difference). The displacement data was converted into strain values by using the Lagrangian strain tensor. R ESULTS ig. 3 shows the representative load-displacement curve of uniaxial tension test on the flat dog-bone tensile specimen with a displacement rate of 5.0 mm/min, which corresponds to an average strain rate of 0.1 min -1 . The curve includes the following stages: the linear elastic stage; the stage of yield drop and plateau forming; the extended stage of material’s hardening; and the post-critical deformation stage. It is important to note that there are a great number of local drops of load or “serrations” on the load versus displacement curves called the Portevin–Le Chatelier effect (PLC) [9]. F