PSI - Issue 42

Florian Garnadt et al. / Procedia Structural Integrity 42 (2022) 1113–1120

1119

F. Garnadt et al. / Structural Integrity Procedia 00 (2019) 000–000

7

(a)

(b)

(c)

cruciform specimen

K t,I =3.4 � �

I =1.7 mm -1

K t,I =4.2 � �

I =1.97 mm -1

Fig. 5. Summary of the main results, (a) in terms of the notch support factor for di ff erent specimen and notch geometries, loading levels and conditions, (b) validation of the computed notch support factors based on the proposed modelling approach of ECG and (c) the cruciform specimen with a center borehole used for transferability check under uni- and biaxial loading.

dimensions and boundary conditions are given by Fig. 6 (a). Plane strain elements were chosen in this two dimensional FE model to represent the loading situation in the thick-walled structure. The result for the crack initiation plus the ECG in this application example is shown in Fig. 6 (b) in form of a shifted fatigue life curve for 1 mm crack depth. Notch support factors can be derived by these results as well. Additionally, curves for other crack depths of interest, e.g., 2, 5 or 10 mm, can be generated by the proposed modelling approach, which then can be used for lifetime assessment. More details on this application example with an additional variation of borehole diameter, material and a mesh sensitivity study are given in Garnadt et al. (2021).

(a)

(b)

U

Exp. fatigue life curve without notch

Shifted fatigue life curve by ECG model for application

10 min

� eq,loc

2 mm

d=4 mm

200 mm

10 mm

a =1 mm

Global Displacement U

10 min

5 mm

U

200 mm

Fig. 6. Application example for the ECG model, (a) 2D representation of a borehole in a thick-walled casing under uniaxial load (displacement controlled) with a dwell time of ten minutes at maximum and minimum load, (b) impact of notch support on the fatigue life curve at 1 mm crack depth by computationally generated cycle numbers and fatigue life curves for additional crack depths.

7. Conclusions

The notch increases the number of cycles for ECG under creep-fatigue loading conditions at high temperature. Based on the investigations of round bar specimens with notch, it turned out that the defined notch support factor for a crack depth of 1 mm depends linearly on the stress gradient. The notch support increases with a higher stress gradient.