PSI - Issue 13

Marijana Milković et al. / Procedia Structural Integrity 13 (2018) 1861 – 1866 Marijana Milkovi ć / Structural Integrity Procedia 00 (2018) 000–000

1864

4

� �� �  m] (trans) �� �� � [MPa]

��� �  m] (long)

Table 1. Test conditions and measurement results from specimen „2“ # N [-] Nt [-] F max [kN]  max [MPa]

R [-]

V [MPa] 13.778 15.333 16.667 17.556

f [Hz]

20.333 29.6667 34 31.6667

0.35239 0.29083 0.27078 0.29222

0.27289 0.33156 0.32956 0.33144

- -

- -

- -

- -

0 0 1 000 10 997 11 997 16 997 67 000 117 741 167 741 706 226

0 0

1 2 3 4 5 6 7 7 8 9

5 5 5 5 5

0.1 0.1 0.1 0,1 0,1 0,1 0,1 0,1

92 92 92 90 90 90 90 90

4.589 4.589 4.589 4.489 4.489 4.489 4.489 4.489

1 000 9 997 1 000 5 000

- - -

- - -

- - -

- - -

50 003 50 741 50 000 538 485

15.333 23.333 22.778

34.2222 9.88889 17.4444

0.31006 0.27661 0.28922

0.34228 0.30856 0.28529

10 10 10

� �� �  m] (trans) �� �� � [MPa]

��� �  m] (trans)

Table 2. Test conditions and measurement results from specimen „3“ # N [-] Nt [-] F max [kN]  max [MPa]

R [-]

V [MPa] 13.778 14.778 15.889 - - - - 24.889

f [Hz]

20.3333 31.3333 41.6667 - - - - 13.4444

0.35239 0.31689 0.30706 - 0.27961 0.28361 0.299 0.2795

0.27289 0.34811 0.29417 - 0.29356 0.31517 0.32089 0.28389

- -

- -

- - 92

- -

- -

- -

1 2 3 4 5 6 7 8

5 5

0.1 0.1 0.1 0.1 0.1 0.1

4.598 5.497 5.497 5.497 5.497 5.497

1 000 6 000 56 000 106 000 156 000 658 122

1 000 5 000

110 110 110 110 110

10 10 10 10

50 000 50 000 50 000 502 122

Figure 3.a) shows the results of measured average values of roughness and residual stresses on specimen „2“ vs. the number of cycles on electropolished surface (2) and the surface that was not electropolished (2+). Figure 3.b) shows the results of measured average values of roughness and residual stresses on specimen „3“vs. the number of cycles on electropolished surface (3) and the surface that was not electropolished (3+). It can be seen that residual stress level of polished surface is always higher than on electropolished one. The manufactured surface conditions have influence only on initial magnitude of residual stress, while level of residual stress degradation is the similar respect to difference between electropolishing and no-electropolishing surface. Both parameters values of roughness and residual stresses are decreasing during fatigue with increasing number of cycles. In order to observe degradation process on the surface of tensile specimen some lines are graved by electron beam, as is shown in figure 4.a) and 4.b). SEM investigation of surface at left upper corner of graver sign of the specimen 3 at magnification x2000 after 6 000 cycles shows figure 5.a), and with the same magnification after 658 122 cycles figure 5.b). a b

Fig. 3 Change of surface conditions due to fatigue: average values of roughness and residual stresses depending on the number of cycles of a) specimen „2“, b) specimen „3“