PSI - Issue 28

L.R. Botvina et al. / Procedia Structural Integrity 28 (2020) 2118–2125 L.R. Botvina et l./ Structural Integrity Procedia 00 (2019) 0 –000

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g h Fig. 2. Deformation curve (measured at N/N f =0, marked with dash line), deformation ,dependencies of the damaged surface area S* and acoustic parameters at different values of N/Nf for specimens of steel 15Cr2MnMoV (a, c, e, g ) and low-carbon steel (b, d, f, h ) : the total number of AE signals (a, b), intensity of AE signals (c, d), b AE -value (e, f ) and the cumulative energy of AE signals (g, h) 3.2. Dependences of damage accumulation on the relative deformation From Fig. 2 it follows that sharp changes in acoustic parameters at the end of stage II of the deformation process occur at a relative deformation equal to ε * ~0.35-0.4, corresponding to the beginning of intensive development of damage, S* , measured at N/N f =0 . Observation of microcracks patterns in specimens made of low-carbon steel shows (Fig. 3) that at ε * ~0.35 the density of microcracks increases, their coalescence begins, and the opening increases.

a c Fig. 3 Microcracks patterns at different values of the relative deformation of the specimen from low-carbon steel in the initial state at N/N f =0: a) 0,35; b) 0,78 and c) 0,95. The minimum measured length of microcracks was ~5 μm b