PSI - Issue 13

Tatyana Tretyakova et al. / Procedia Structural Integrity 13 (2018) 1739–1744 Author name / Structural Integrity Procedia 00 (2018) 000–000

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thickness, and, as a consequence, a macroscopic fracture of material. In recent years, a large number of experimental data have been accumulated on the temperature-rate regions of the serrated yielding effect, the effect of the chemical composition, microstructure parameters, and scale effect for various classes of materials [Wang et al (2017)]. Most of the results are obtained under uniaxial loading, that restraints formulation of adequate predicting models of the inelastic behavior and fracture of structures and materials, taking into account actual operating conditions and plastic flow characteristics. Predicting behavior of materials at set operational conditions, design newmaterials and technologies require a better understanding of principles and specifics of inelastic deformation and fracture in metals under serrated yielding; establishing and describing the relation between instability and macroscopic localization of plastic flow depending on the type of stress state and complex loading. The aim of the present work was to investigate the occurrence of the Chernov-Lüders deformation and the Portevin Le Chatelier (PLC) effect in a carbon steel and an Al-2 % Mg alloy during uniaxial tension tests in dependence on the additional vibration impact based on the registration and analyzing the kinetics of strain and temperature fields, acoustic emission signals. Furthermore, this study is aimed at developing methods on experimental study with multi parameter identification of experimental data by a combined use of the testing equipment, non-destructive methods and non-contact optical systems under specified operating conditions. 2. Materials and methods 2.1. Materials and specimen geometry The materials studied in this investigation is the aluminum-magnesium alloy (GOST 4784-97, 2.2Mg, 0.6Mn, 0.4Fe and 0.4Si, %) and the carbon steel (GOST 1050-88, 99Fe, 0.18C, 0.20Si. 0.35Mn, 0.04Cr, 0.03Ni, 0.04Cu, %). The two groups of plane specimens were manufactured by the method of hydro-abrasive treatment from rolled sheets of Al-Mg alloy and steel 20 of thickness 3.0 mm. Materials were tested in the state as received without additional temperature processing. Uniaxial tension loading experiments (without/with additional vibration impact) were carried out with the dog-bone specimen (the thickness h of the specimen is 3.0 mm, the gauge length l 0 is 14.0 mm, the width b for carbon steel specimen is 30.0 mm and for the Al-Mg alloy 0 20.0 l  mm). 2.2. Experimental procedure Specimens were deformed in tension with a biaxial (tension/torsion) servo-hydraulic testing system Instron 8850 at room temperature and at the rate of 2.0 mm/min. The research program includes mechanical tests on uniaxial tension tests and tensile tests with additional vibration impact. The vibration impact was carried out with the tension load and at the frequency of 4 Hz with a sinusoidal waveform (see Fig. 3, curves u t  ). The evolution of inhomogeneous strain and temperature fields was registered by using the 3D-digital-image correlation measurement system Vic-3D and the infrared camera (with a resolution of 640×512 pixels) Flir SC7700 (see Fig. 1 (a)). The kinetics of deformation bands and some parameters (velocity, width, angle, heterogeneity coefficient, etc.) were investigated through strain and temperature field measurements. The images were captured with a pair of two CCD black/white cameras (Prosilica, 16 Mp resolution) at a frequency of 3 Hz by using a commercial software package called ‘Vic-Snap’. The heterogeneous fields of longitudinal ε yy , transverse ε xx and shear strain ε xy were calculated using the Lagrange tensor with the Oy axis directed along the tension axis and the Ox axis was perpendicular to it. The mechanical behaviour and the regularities of the jerky flow were studied using analysis of stress serrations and the accompanying acoustic emission (AE) by AMSY-6 (Germany). The two wide band sensors AE105A (450-1150 kHz), preamplifiers (40dB) were used for testing. The sensors were attached to the surface of the specimen with the help of a cyanoacrylate glue. The location of mounted AE-sensors is shown in Fig. 1 (b). AE signals were recorded in a continuous mode during the tests. In the case of additional vibration impact, there was registered the decrease of the duration, activity and the energy parameter of AE events [Illkova et al (2014)].