PSI - Issue 43

Robert Szlosarek et al. / Procedia Structural Integrity 43 (2023) 41–46 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

44 4

Fig. 3. (a) section view of the finite element model; (b) simulation procedure.

The fatigue material data are taken out of the reference Boller and Seeger (1987). Table 1 depicts the used parameters. In the reference the parameters were determined by 45 tests of cyclic loading with R=-1. The yielding and fracture limit of the material in the reference is similar to the used material.

Table 1. Material parameters used in the fatigue analysis. Parameter

Fatigue strength coefficient ′ Fatigue strength exponent Fatigue ductility exponent Fatigue ductility coefficient ′ Cyclic strain hardening exponent ′ Cyclic strength coefficient ′

Value 1193 -0.11 -0.553 0.6601

(MPa)

(-) (-) (-) (-)

0.185 1296

(MPa)

3. Results 3.1. Numerical contact pressure distribution

Fig. 4 depicts the contact pressure distribution of several preloads of the bolt. The stress scale is normalized to the yielding limit of the material. For preload of 0 kN arises no pressure in the contact zone. With an increasing preload the contact pressure also increases. Notably is that for low preloads there is a maximum at the outer circumference of the contact zone and for high preloads at the inner circumference. This is motivated by the geometry of the nut. The pressure disk of the nut is inclined whereas the outer circumference is at bottom. Due to the preload the pressure disk gets deformed to a plain plate. The contour plots also show that for a preload of 225 kN the yielding limit at the inner circumference is exceeded. This indicates a sticking between the nut and the sheet material. Similar findings are visible by observing the contact zone between the spacer and the sheet. The results indicate that the borehole is knuckled by the bolt joint.