PSI - Issue 20

N.A. Makhutov et al. / Procedia Structural Integrity 20 (2019) 63–74 N.A. Makhutov and V.V. Zatsarinnyy / Structural Integrity Procedia 00 (2019) 000–000

66

4

Table 1. The average experimental characteristics of the mechanical properties of steel 15H2NMFA at room temperature. Characteristic MMP σ в , MPa σ т , MPa σ 0,2 ,MPa S k , MPa Ψ k ,% δ ,% Average 690 559 582 1642 78,2 23,8 Coefficient of variation, ν 0,0266 0,0371 0,0381 0,0258 0,01 Values at P=0,05 660 525 545 1576 77 21,7 Values at P=0,01 648 511 529,5 1548 76,4 20,8 Table 2. The values of the coefficients of variation of the basic mechanical properties of steel 15H2NMFA at room and elevated temperatures. Characteristic v � в v � ��� v � Т v � � � � ������ v � � ������� Temperature, 0°С 20 350 20 350 20 350 20 350 20 350 20 Experimental 0,0266 0,0401 0,0379 0,0593 0,0372 0,0735 0,01 0,0724 0,0313 0,0724 0,0215 Some peculiarities of fracture resistance at the neck of a specimen S k can be noted (Fig. 2). In case no direct experimental data about S k values is available the correlation relationship between S k and basic MMP characteristics - σ B , ψ k – may be used Makhutov (1981). � � � в �� � ��� � � � (1) Average experimental S k value at Р = 50% probability is 1643 MPa, whereas the average calculated value defined according to (1), with the use of average values of characteristics, is S kcalc = 1448 MPa. The calculation curve of normal distribution for S kdirect built according to (1) for the same range of probabilities (30 values) is presented (in comparison with S kexp experimental value) on the Fig. 2. As S k direct < S k exp , the application of the calculation expression (1) contributes to safety factor. In order to ascertain the impact of ultimate plasticity ψ k (plasticity grows with the increase of probability P - ψ k direct and vice versa – ψ k inverse ) on the course of the curves describing S k distributions according to formula (1) two distributions S k direct and S k inverse (Fig. 2) were computed. It is apparent that the average values of both computed distributions are lower and constitute about 0.88 of S k experimental values (Table 3). Table 3. Comparison of the average experimental and calculated characteristics of the rupture strength in the neck S k for steel 15H2NMFA. Type of characteristic, S k S k , MPa (average) Coefficient of variation, ν Sk Error, Δ Sk (ratio of exp. value) , %

ψ� k

0 0

78,3

Experimental, S kэ

1643

0,0251

̅ � ���� ̅ � ��� � ����� ν ���� ν ��� � ���� ̅ � ���� ̅ � ��� � ����� ν ���� ν ��� � �����

ν ψk

0,009*

Calculated , S k direct

1448

0,0313

78,3

Calculated inverse, S k inverse .

1448

0,0215

ν ψk 0,009* Note . In the “Error” column the numerator is composed of average calculation values �� �� � �� � � and coefficients of distribution variations ν calc , and the denominator – of average experimental values �� � exp and their variation coefficients ν exp. * – the variation coefficient accepted in calculations.