PSI - Issue 5

Tatyana Tretyakova et al. / Procedia Structural Integrity 5 (2017) 318–324 Tatyana Tretyakova et al. / Structural Integrity Procedia 00 (2017) 000 – 000

319

2

necking effect at the postcritical deformation stage [Vildeman et al (2016)]. During uniaxial tension tests this irregular plastic flow results in the bands of localized plastic deformation, or the Chernov- Lüder’s bands [Krishtal (2004), Avril et al (2008)]. Inhomogeneous plastic flow reduces the surface quality of the material, causes the premature corrosion and increases the probability of unstable failure. Material characterization has always played one of the main role and many procedures have been developed through the recent years to solve high-precision measurement and identification issues. The developing of the methods on experimental mechanics allows providing estimations of mechanical behavior of the metals and alloys under complicated thermomechanical impacts, which are close to the operating conditions. In this paper, the aim is to study the temporal instabilities of the plastic flow and postcritical deformation in specimens with concentrators based on the analysis of the inhomogeneous strain and temperature fields, to study the processes of the damage accumulation and crack propagation during uniaxial tension tests. In order to analyze the damage tolerance of materials and structural integrity, the real evolution of the postcritical deformation zone was identified on the surface of the specimens with concentrators based by using nondestructive testing methods. The experimental database can be used in numerical investigations of the spatial-time inhomogeneity of the plastic deformation, the mechanical behavior of metals and alloys with considering of the real conditions of the impact. 2.1. Material The experimental studies were carried out on the carbon steel (C1010). The chemical compassion is Fe ‒ 98.7 %, C ‒ 0.2 %, Si ‒ 0.23 %, Mn ‒ 0.39 %, Cr ‒ 0.14 %, Cu ‒ 0.2 % . The microstructure of the material is shown in Fig. 1; the average grain size was 27 µm. The phase analysis revealed that the proportion of the ferrite of the steel as a structural component was 70 % and perlite – 30 %. The flat specimens were cut from a sheet metal of C1010 by water jet cutting. Material was tested in the state as received without additional temperature processing. The research program included tests on the uniaxial tension of the flat dog-bone tensile specimens with the gauge length and width of 100 mm and 20 mm accordingly, the thickness of 3 mm. The samples were made in accordance with the Russian Standard GOST 1497-84 «Metals. Test Methods on Tension». The main part of the experimental program included the tension tests of the flat specimens with concentrators of different geometry. Sketches of the samples with a single hole, a central crack-like notch and with a rhomb-shaped notch are illustrated in Fig. 1. 2. Material and experiment procedure

a

b

Fig. 1. (a) microstructure of the carbon steel (C1010); (b) sketch of the flat specimens with concentrators of different geometry: a single hole, a central crack-like notch and a rhomb-shaped notch.