PSI - Issue 59

Pavlo Bulakh et al. / Procedia Structural Integrity 59 (2024) 253–258 Pavlo Bulakh / Structural Integrity Procedia 00 (2019) 000 – 000

257

5

No specimen

Material

m 0

m z

m θ

m rel.z

m rel. θ

m z /m θ

ε zp , %

23.11 18.88 42.34 40.34 32.15 40.34 32.92 27.97 83.958

37.58 32.32 64.79 63.59 46.64 56.62 51.06 44.93 93.583

0.218 0.211 0.382 0.718 0.345 0.289 0.308 0.319 0.258

0.355 0.361 0.585 0.799 0.544 0.419 0.432 0.495 0.415

0.625 0.584 0.653 0.897 0.634 0.689 0.712 0.645 0.623

18.4 18.6 13.8 6.08 14.2 14.2 14.8 15.0 14.45

N3 N1

89.57

110.75

N2

117.0

N3 N4 N5 N6

111.17 131.09 103.07 108.31

15Kh2NMFA

The above-mentioned differences in the relative values of the homogeneity coefficients m rel. θ and m rel.z are quite clearly correlated with the photographs of the metal microstructure of the neck of the specimen in the longitudinal and transverse sections before failure, presented, as an example, for one of the studied steels in Fig. 3. These photographs show the difference between the microstructures of the damaged metal in the longitudinal (unidirectional structure) and transverse (multidirectional) directions.

b

a

Fig. 3. The microstructure of the deformation neck of the 15X2MFA steel specimen in the longitudinal section (a) and cross-section (b) before fracture.

These data indicate a higher level of damage to the metal in the transverse direction of the specimen, that is, to a lesser degree of loosening of the metal compared to damage in the longitudinal direction at a certain critical value of the longitudinal strain ε zp (Giginyak et al. (2010), Marushchak et al. (2015)). The specified multidirectional structure in the transverse direction is probably a more favorable environment for the development of shear deformation in contrast to a unidirectional structure. Based on the obtained data, the diagrams m rel.z /m rel.  – ε ip were constructed (Fig. 4). At the same time, only the three largest values of ε ip for each studied material, which are closest to the ε ip determined after the fracture of the specimen, were used. Based on the results of this work, we can assume that the critical value of the ratio m μ corresponds to the limit state of individual structural elements of the metal, which is determined experimentally for the studied material.