PSI - Issue 19

Kim Bergner et al. / Procedia Structural Integrity 19 (2019) 140–149 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

145

6

fatigue investigations of the bending specimens from the bulk material and of the specimens with surface roughness and with casting skin (rim zone and surface roughness) are shown in Fig. 6.

Table 3. S-N curve parameters of EN-GJS-400-15 bending specimens

S-N curve parameters

σ a [MPa]

k [-]

N k [-]

T σ [-]

R = 0

EN-GJS-400-15 Bulk material

1∙10 6 1∙10 6 1∙10 6 1∙10 6 1∙10 6

12.0

201 165 109 114 111

1:1.10 1:1.13 1:1.32 1:1.32

Surface roughness

9.0

Rim zone (GE_I + GE_II) GE_I: Pearlitic Rim

10.9 11.9 12.5

GE_II: Ferritic Rim 1:1.30 In order to consider the varying thickness of rim zones in cast components within the fatigue assessment, a rim zone factor n RZ was determined for each fatigue test. The rim zone factor n RZ describes the deviation in stress-direction between the individual fatigue results and the S-N curve for rim zone free material and is calculated by equations (3) and (4). = , , =0 (3) , =0 = . ∙ ( ) 1 (4) Plotting the rim zone factor against the mean rim zone thickness t RZ of each tested specimen shows a good correlation for rim zone thicknesses up to 2 mm, Fig. 7, which can be expressed by equation (5). = 0.0798 ∙ 2 ± 0.3924 ∙ + 1 (5)

Fig. 7. Relation between rim zone factor n RZ and mean rim zone thickness t RZ

2.6. Results of the strain-controlled fatigue tests

Table 4. Parameters of the strain life and cyclic stress strain curves

Material

E [MPa]

b

c

n'

K'

 f '

 f '

Bulk material (EN-GJS-400-15) 159 000

564.5 557.9

0.08632 0.00923

-0.0836 -0.1396

-0.5895 -0.3794

0.1418 0.3683

799.0 3133

Rim zone

130 000