PSI - Issue 13

Fidan Smaili et al. / Procedia Structural Integrity 13 (2018) 1347–1352 Fidan Smaili, Tomaž Vuherer / Structural Integrity Procedia 00 ( 2018) 000 – 000

5

1351

R2

 18

 12

K t

R2

 18

 12

K t

K t

K t

 10,35

b  16,35

K t

a

c

Fig. 7. (a) Weld with stress concentration K t ; (b) specimen for rotary bending test with K t ; (c) Specimen for bending test with K t

K t

R3  10,35

 16,35

Artificial defect were made at the bottom of the groves of the specimens by diamond Vickers indenter. Figure 8 shows details of artificially made defect, where diagonal is 200 µm and depth is 28 µm. Parameter area which is normal projection on loading plane and its value is 54 µm. Artificial defect was prepared on each specimens by indenting after CG HAZ or FG HAZ microstructure preparation. R3

d

h

a c Fig. 8. (a) Geometry of the of defect (d = 200 mm and h = 28 µm) ; (b) Vickers impress (SEM), determination of the area parameter (54 µm) Non propagating crack initiated from the artificially made defect (Vickers impress) occurred on the specimen with CG HAZ microstructure, which is rotary bended and loaded by bending stress 664 MPa with R ratio -1 what is below fatigue limit. Specimen did not break after 2 million cycles. Non propagating crack is shown in Figure 9a and marked by red arrows. Photo is taken on SEM microscope QUANTA 3D. Figure 9b represent Crack propagation from artificially made defect in FG HAZ where is shown top view taken by Leica Wild 10 M microscope Specimen was loaded with bending stress 700 MPa what is above the fatigued limit, which is 525.

r

r

r

a b Figure 9. Non propagating crack initiated from the artificially made defect made by Vickers impress (SEM); (a) left side; (b) right side

4. Conclusions

 Influence of the CG HAZ and FG HAZ microstructures on threshold and fatigue crack propagation were analyzed on simulated HAZ microstructures in furnace on steel CT 781.