Issue 27

T.V. Tretiakova et alii, Frattura ed Integrità Strutturale, 27 (2014) 83-97; DOI: 10.3221/IGF-ESIS.27.10 83 Study of spatial-time inhomogeneity of serrated plastic flow Al-Mg alloy: using DIC-technique T. V. Tretyakova, V. E. Wildemann The Center of Experimental Mechanics, Perm National Research Polytechnic University, Komsomolsky Av. 29, Perm, 614990, RF cem.tretyakova@gmail.com A BSTRACT . The aim of the present paper is the investigation of temporal instabilities and spatial localization due to the Lüders behavior, the Portevin–Le Chatelier effect and the shoulder or necking effect during uniaxial tension tests of aluminum-magnesium alloy. This paper presents the brief description of the test procedure and experimental results of carrying out research by the combined use of a servo-hydraulic biaxial test system Instron 8850 and a non-contact 3-D digital image correlation measurement system Vic-3D. The digital image correlation 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 evolution of inhomogeneous axial strain and axial strain rate fields has been illustrated for each stage of material’s deformation. To estimate the kinematics of serrated or jerky flow due to the strain bands propagation, the strain versus time curves and strain diagrams are given here. The experimental results show the recurrence in the strain distribution leveling along the specimen gauge. The changing between the macroscopic localization of the plastic flow, namely the running of the Lüders and PLC bands and the recovery of strain field homogeneity, has been observed. K EYWORDS . Portevin–Le-Chatelier effect; Serrated plastic flow; Yield plateau; Aluminum-magnesium alloy; Digital Image Correlation. I NTRODUCTION or projecting and numerical model’s development of structures should be taken into the account not only mechanical and strength characteristics of materials, but also its behavior singularity. There are a lot of studies concerning the deformation and fracture processes in materials, occurring irregularly on all scales of observation: micro-, meso- and macroscopic scales [1, 2]. Theoretical and experimental research of temporal instabilities and spatial localization during the tensile tests of different metals and alloys has been conducted for more than two hundred years all over the world [1–4]. The main types of macroscopic occurrences of the plastic deformation inhomogeneity are: the Lüders bands nucleation at the stage of the yield drop and plateau forming; an irregular plastic flow appearing either as the staircase phenomenon on the stress versus strain curves – the so-called Savart–Masson effect during force loading – or the serrated or jerky flow due to the Portevin–Le Chatelier (PLC) effect during kinematic loading [5–12]. Another widespread example of spatial inhomogeneity is the shoulder or necking effect at the postcritical deformation stage, which F