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

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localization (Botvina and Petersen 2001; Botvina et al. 2005). Thus, the analysis of changes in the b AE -value allows one to obtain additional information about the kinetics of the processes of fracture and emission of acoustic signals, which is difficult to analyze only by the AE activity (Botvina et al. 2015). a b

c

d

Fig. 1. Stress-strain diagrams of smooth specimens from low- carbon (а -b) and austenitic stainless (c-d) steels, combined with deformation dependencies of AE activity, b AE -value and self-magnetic field intensity H r (a, c), as well as the deformation dependencies of the magnetic field intensity evaluated by eddy current method H EC and coercive force H C (b, d). Thus, the assessment of physical characteristics showed that the sensitivity of the applied methods of non destructive testing varies significantly at different fracture stages. The characteristics of the metal magnetic memory and acoustic emission exhibit the greatest changes at the initial stage of fracture at the yield point, while the eddy current parameter and coercive force most informatively reflect the processes occurring at the stages of strain hardening and the multiple damage development. The main results of damage assessment at tension of the steels under study are given in (Botvina et al. 2017). Analysis of the obtained results showed that the dependences of the relative area of the damaged surface ( S *) on the deformation (fig. 2a) are significantly different for low-carbon and stainless steels. At the initial stage of loading, the damage in stainless steel is higher than in low-carbon one. With further deformation, damage in low-carbon steel becomes substantially higher (fig. 2a). This indicates a higher rate of damage accumulation in last one. The kinetic damage curve of low-carbon steel was plotted according to the Kachanov-Rabotnov relation. As can be seen from the Figure 2b, the diagram is described by a power low with the index m equal to 13.5 (see equation 1). There were not enough experimental points to plot a kinetic damage curve for stainless steel, we plan to perform a similar analysis later.