PSI - Issue 28

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

2124

7

the values obtained at other stages. In a stronger 15Cr2MnMoV steel, the accumulated number of AE signals is higher than in low-carbon steel, and b AE -value increases with an increase in the relative number of cycles in stages III-IV, in contrast to low-carbon steel. The dependences of the main acoustic parameters on the relative durability of 15Cr2MnMoV steel are well described by exponential functions with values R 2 = 0.95÷0.98:

/ dN dt

exp( 3,1 /

)

N N



   

(2)

AE

f

exp( 1, 3 / ) N N  

N





(3)

AE

f

exp( 2, 3 / ) f N N    

(4)

The acoustic activity of low-carbon steel is also well described by an exponential function with the coefficient of determination R 2 = 0.99:

/ dN dt

exp( 5, 7 / ) N N



   

(5)

AE

f

From the ratios (2), (5), it follows that the exponent in relation for low-carbon steel is about twice as large as for 15Cr2MnMoV steel. This may be cause of a sharper decrease in the average intensity of acoustic signals in low-carbon steel with an increase in relative durability. The above relations can be used to diagnose the state of material under cyclic loading by means of estimation of changing the parameters of acoustic emission. The more universal parameter, as can be seen from Fig. 4 a, b, is the average activity of acoustic signals. Conclusions 1. The stages of changes in acoustic emission characteristics during the tensile fracture of two structural steels with bainite and ferrite-perlite structure after preliminary cyclic loading to different values of relative durability were studied. 2. The relations connecting the parameters of acoustic emission with the relative number of pre-loading cycles were established. 3. General and particular dependences of changes in the acoustic emission characteristics of the steels studied with changes in the relative number of pre-loading cycles were discussed.

Acknowledgements The study was supported by the Russian Science Foundation (project № 19-19-00674). References

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