PSI - Issue 65

Kuskov K.V. et al. / Procedia Structural Integrity 65 (2024) 133–138 Kuskov K.V./ Structural Integrity Procedia 00 (2024) 000–000

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3

3. Results and discussion

The test results are presented in Tables 2-5.The Locati method provides the fatigue curves family construction for the failure probabilities of 10, 50 and 90%. The S-N curves are taken as the average conditional curve (see Agamirov L. V. and Vestyak V. A. (2020); Jihed Zgal et al. (2016); Trofimov O.F. (2012); Fabian Weber at al. (2023)). They are taken from the literature data. The upper and lower fracture points of the fatigue curve are calculated according to the equations (see Metodicheskie ukazaniya (1990); Taranova E. S. and Tyurin S. A. (2012); Lyalyakin V. P. (2021)):

N N G l G * 3 2 

lower limit

(1)

N N G U G

* 1,5  upper limit

(2)

where N G * - is the abscissa of the S-N curve fracture point. Further, the sums of relative durability are calculated for each curve according to formula 3. ( / ) i i n N 

(3)

where i n - is the number of cycles at the loading stage; i N - is the number of cycles corresponding to the fatigue curve. The fatigue curve fracture point is chosen 2*10 6 cycles (see Metodicheskie ukazaniya (1990)) for the studied steels. The fatigue strength of steels for various roughness directions is determined according to the graphs plotted in coordinates Σ(n i /N i ) - σ -1 . Figure 3 shows an example of such graph for the 30KhGSA steel. Table 6 shows an example of processing fatigue test results using the Locati method for plotting graphs in coordinates Σ(n i /N i ) - σ -1 . The three sample values are averaged. The results are shown in table 7.

Table 2. Accelerated test results for steel 35

Cycle numbers, unit.

Stage Stress, МPа

Sample 1 Series 1

Sample 2 Series 1

Sample 3 Series 1

Sample 1 Series 2

Sample 2 Series 2

Sample 3 Series 2

136.4 181.8 227.3 272.8 318.2 363.7

72000 72000 72000 72000 42350

72000 72000 72000 72000 33920

72000 72000 72000 72000 54600

72000 72000 72000 72000 72000

72000 72000 72000 72000 72000

72000 72000 72000 72000 71690

-

-

-

3000

5703

-

Table 3. Accelerated test results for steel 30KhGSA

Cycle numbers, unit.

Stage Stress, МPа

Sample 1 Series 1

Sample 2 Series 1

Sample 3 Series 1

Sample 1 Series 2

Sample 2 Series 2

Sample 3 Series 2

251.5 335.4 419.2 503.0 586.9 670.7

72000 72000 72000 72000 72000

72000 72000 72000 72000 72000

72000 72000 72000 72000 72000

72000 72000 72000 72000 72000

72000 72000 72000 72000 72000

72000 72000 72000 72000 72000

5400

9210

6340

6630

8630

5070