PSI - Issue 23

M.R. Tyutin et al. / Procedia Structural Integrity 23 (2019) 559–564 M.R.Tyutin , L.R.Botvina, V.P.Levin and I.O.Sinev/ Structural Integrity Procedia 00 (2019) 000 – 000

560

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structures and machine parts, requires a comprehensive and step-by-step analysis of the evolution of real damage of structural materials by a direct method for various types of loading and establishing a correlation of obtained data with physical characteristics. In (Botvina et al. 2017, 2016), the results of such analysis on structural steel specimens are presented. Authors used a set of research methods, including the method of acoustic emission, magnetic memory, optical microscopy and statistical image analysis. This work is devoted to the analysis of changes in the magnetic and acoustic characteristics of non-destructive testing and to the establishment of the relationship of physical parameters with real damage, as well as to the study of the kinetics of damage in specimens of low-carbon and stainless austenitic steels.

Nomenclature b AE

slope coefficient of the amplitude distributions of the acoustic emission signals

Ṅ AE

accumulation rate of acoustic emission signals intensity of the resulting self-magnetic field

H r

H EC

magnetic field intensity, estimated by the eddy current method

H C S *

coercive force

relative area of the damaged surface

2. Materials and methods

The study was carried out under tension conditions on flat specimens (with sizes 220x40x6 mm, gauge section sizes are 80x20 mm) from structural low-carbon 0.2%C steel and austenitic stainless Cr-Ni-Ti steel commonly used in industry. Table 1 presents the chemical composition and standard mechanical properties of the investigated steels.

Table 1. Chemical composition (%, mass.) and standard mechanical properties of studied steels

σ YS , МПа

σ U , МПа 435,3±4,2

Steel

C

Si

Mn

Ni

Cu

Cr

Mo

Ti

El., %

36,7±3,1 71,3±3,1

283±4,7

Low-carbon

0,169

0,212 0,278

0,357 0,909

0,0354

0,0693

0,0468

-

-

234,2±4,1

593±6,1

Stainless

0,07

9,52

0,358

18

0,246

0,35

The acoustic emission (AE) parameters and the self-magnetic field intensity were evaluated in the process of deformation. The magnetic field intensity by the eddy current method and the coercive force were measured at different stages during stops in loading. The percentage of martensitic phase in stainless steel was evaluated by eddy current technique. Damage assessment of the studied steels was performed using an optical microscope during stops at different stages of deformation. The following characteristics were evaluated:

 accumulation rate of acoustic emission signals Ṅ AE ;

 slope coefficient of the amplitude distributions of the AE signals ( b AE -value) (Botvina and Petersen 2001; Botvina et al. 2005, 2016; Shiotani, Bisschop, and Van Mier 2003; Carpinteri, Lacidogna, and Puzzi 2009);  intensity of the resulting self-magnetic field ( H r ), estimated by the metals magnetic memory method (Dubov et.al. 2012);

 magnetic field intensity ( H EC ), estimated by the eddy current method;

 coercive force ( H C );  length ( l c ), total number (Σ N c ) of microcracks and relative area of the damaged surface ( S *).