Effect of Strain Aging on Stages of Plastic Strain and Tensile Fracture of Specimens of Steel 08G2B. Part II. Stage of C
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EFFECT OF STRAIN AGING ON STAGES OF PLASTIC STRAIN AND TENSILE FRACTURE OF SPECIMENS OF STEEL 08G2B. PART II. STAGE OF CONCENTRATED STRAIN V. M. Farber,1 V. A. Khotinov,1 O. N. Polukhina,2 O. V. Selivanova,1 A. N. Morozova,3 and D. I. Vichuzhanin4 Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 46 – 50, July, 2020. Periods of the stage of concentrated strain of specimens of low-carbon steel 08G2B with ultrafine structure are studied by joint analysis of stress–strain curves and fields of digital image correlation (DIC). The DIC data and detection of a through crack on the surface of a tensile specimen are used to justify the use of the parameters of the second period of the stage of concentrated strain as criteria of crack resistance. Experimental data are used to determine the main factors representing the influence of strain aging on the level of mechanical properties of the steel.
Key words: strain localization at neck, plastic instability, stage of concentrated strain. length of the concentrated stage dc is almost halved (from 8.4% to 4.4%) and the failure stress sf grows from 345 to 620 MPa. This is accompanied by increase in the ratio sf /sr (0.53 ® 0.76 ® 0.84 for specimens I, II, III, respectively, Fig. 1). The fields of displacement component eyy and the profiles of its distribution over the length of the specimen Lsp on sr and in the concentrated stage are given in the stress–strain diagrams for the respective points in Fig. 2. The evolution of the structure-and-strain picture in the concentrated tension stage is similar for all the specimens studied. The effect of the prehistory of the specimens, which is responsible for the differences in the characteristics of the yield plateau and in the stage of strain hardening, is manifested in the concentrated stage in displacements of single-type processes over the extension scale d (deformation time t). The strain source (SS) is localized rapidly upon transformation of the leading maximum into a functional one, which grows intensely at an increasing rate; its height increases abruptly, and the width at half the height decreases on about the same base (Fig. 3). Within the macroapproach, the strain hardening in the uniform stage is described by the Hollomon equation [2]:
INTRODUCTION In the first part of the work, we have considered two kinds of Luders deformation on yield plateau. It has been shown that the deformation inside a Chernov–Luders band at the start of its formation is ³ 14%. The stress–strain curve describing the stage of strain hardening has been divided into linear and exponential regions. We have also analyzed the factors determining the functioning of these stages. The chemical composition of the studied steel 08G2B, the heat treatment modes and the test methods are described in [1]. RESULTS The plastic flow of metal in the concentrated stage is determined by the processes occurring on the yield plateau and in the stage of uniform strain. Specimens with different strain aging effects (SAE), which are characte
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