PSI - Issue 36

V. Kharchenko et al. / Procedia Structural Integrity 36 (2022) 277–283 A.V. Sereda et al. / Structural Integrity Procedia 00 (2021) 000 – 000

279

3

indentation method as a more efficient non-destructive control test procedure. The non-destructive control methods for the mechanical characteristics of high-strength steels can be used as an initial approval of metal products. 2. Materials and Methods of Investigation The sheet products of high- strength steels 28GkhNMP (Armox 500Т), 20GR (Xardox 450) with 10 mm in thickness and steels 30Kh2SN2MFА (steel 71), 28GRA (Miilux 500) of 6 mm in thickness as delivered (used for special-purpose structures) are used to approbate the procedures of the strength characteristics for high-strength steels from the instrumented indentation results. Figure 1 illustrates the scheme of the cutouts and specimens for testing.

Fig. 1. Scheme of cutouts and specimens for testing: 1 – uniaxial tension, 2 – hardness and indentation measurement, 3 – metallographic investigations..

The investigation of the mechanical characteristics of sheet materials was performed using various methods, namely: uniaxial tension, Brinell hardness, and instrumented indentation method in two orthogonal directions (along and across). The uniaxial test specimens were cut in two orthogonal directions. The tests were performed in compliance with ISO 6892-1:2019 using Instron 8802 at room temperature. Here the proportional cylindrical specimens were used. The strain measurement was performed via automatic strain registration using the strain gauge transformer. The strength characteristics from the test data were determined according to. The test specimens using the Brinell hardness and instrumented indentation were made also in two orthogonal directions from the same metal sheets (see Fig.1). The hardness tests were made on the stationary hardness testing machine KhPO with balls of 2.5 and 10 mm complying with standard DSTU EN ISO 6506-1:2019. Instrumented indentation was carried out according to ISO 14577-1:2015 in the cyclic loading mode with a ball of 2.5 mm on laboratory setup UTM-20HT (Katok et al. (2019)) designed at the G.S. Pisarenko Institute for Problems of Strength of the NAS of Ukraine. A mobile setup RIIT-02 was designed to determine the strength characteristics of structural materials for technical items under factory conditions using the instrumented indentation method (Kharchenko et al. (2009)). The procedure involves the obtaining of correlation dependencies between the mechanical characteristics, which were received from the uniaxial tensile test results and cyclic indentation diagram parameters. 0,2 p R indent was determined in indentation by the procedure in (Haggag (2007)). The correlation dependence between the evaluated offset yield limit and parameter А from the tensile test data was obtained for carbon steels. It defines the material plasticity limit in the equation describing the indentation diagram in coordinates

F

D d

«

–

»:

2

d

0 , 2  a A b  +

R p0.2 indent =

,

(1)



0 , 2

0,2 b  are the coefficients that are experimentally determined according to standard ( SОU -56-28

0,2 a  and

where 2018).