PSI - Issue 19

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

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Table 5. Used fatigue approaches and their parameters

1. FKM guideline

2. Strain-life approach (FEA with rim zone)

3. Strain-life approach (rim zone factor)

FE-Model

Load-strain relation

Material behavior

Linear-elastic

Elastic-plastic

Elastic-plastic

n  ,rim zone = 1.33 n  ,bulk material = 1.29 K R,  rim_zone  = 0.9 K R,  bulk material  = 1

Support factor

n  = 1.25

n  = 1.25

Surface roughness factor

K R,  = 0.9

K R,  = 0.9

Mean stress sensitivity

M = 0.41

M = 0.41 n RZ = 0.7

M  = 0.22

Rim zone factor

-

-

2. Strain-life approach considering the rim zone in the FE analysis For the strain-life approach, the local stresses and strains were derived in elastic-plastic FE analyses with an addition layer for the rim zone with a thickness of t RZ = 1 mm. The rim zone layer is modelled with a material behavior shown in Fig. 9; the material behavior for the bulk material is shown in Fig. 8. In this approach, two hot spots were evaluated, one in the rim zone and one in the bulk material. The damage parameter P SWT according to [16] was used to consider mean stresses. This P SWT shows a mean stress sensitivity of M = 0.41 in the range from R = -1 to R = 0. For the calculation of the stress-strain hysteresis, the Masing-Memory [17, 18] behavior was used. 3. Strain-life approach considering the rim zone factor The FE model used to derive the stresses and strains for the third fatigue approach is modelled without an additional layer for the rim zone. Instead, the whole specimen is modelled with bulk material, Table 5. The rim zone is considered in this approach using the rim zone factor n RZ .