PSI - Issue 43

Matthias Oberreiterr et al. / Procedia Structural Integrity 43 (2023) 240–245 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

244

5

Table 3 Summary of defect sizes as well as calculated fatigue strength for a probability of occurrence of 50% compared to experimental results

50%

[µm] [-] σ , ,50% [-]

Tiryakioğlu σ , ,50%

[-] Murakami σ , ,50%

[-] Experiments Δ Tiryakioglu

[%] Δ Murakami [%]

Position & Defect

A, P, frac. A, P, CT B, P, frac B, P, CT

94.9

0.86 0.89 0.37 0.88 0.62 0.97

0.96 0.97 0.57 0.58 0.93 0.80

0.84 0.82 0.53 0.53 1.00 0.93

1.00 1.00 0.56 0.56 0.97 0.97

3.6 2.5

16.2 17.7

105.8 487.7 483.4 120.2 184.9

-1.9

5.8

5.6 4.6

-3.5 -2.4

C, P+I

C, P+I+B

17.8

4.7

Fig. 4 (a) Fatigue assessment methodology by Tiryakioğlu and (b) C omparison of methods by Murakami and Tiryakioğlu with experimental data

In contrast, the model of Murakami results in conservative fatigue design of ‘P osition A ’ for defect sizes evaluated by fractography and CT by about 16% up to 18%, see Tab. 3. But ‘P osition B ’ , possessing larger defects, can be estimated conservatively by 5.8%, using a model with 2 = 0 , as proposed by Aigner et al. (2018). ‘ Position C ’ can be well assessed by Eq. 3. Considering pores (P), inclusions (I) and bifilms (B) leads to a slightly conservative fatigue design by 4.7%. In contrast, considering only P+I lead to non-conservative fatigue strength of -2.4%. Fig. 4b represents the comparison between the appl ied models of Tiryakioğlu , denoted with T in the legend, and Murakami, marked with M. The green colored area represents the interval for maximum 10% conservative fatigue design, whereas the red colored section represents the opposite non-conservative border. Additionally, the effect of different set-values for probability of survival is indicated as data-point label. The calculated and experimental scatter bands show the same tendency as the mean value, but can lead to more conservative, or non-conservative, fatigue designs for high or low probabilities of survival. 4. Conclusions A detailed application of fatigue strength assessment models by Tiryakioğlu and Murakami is presented within this study. Extreme value defect distributions are evaluated both by fractography and computed tomography. Furthermore, the fracture initiating mechanisms were analyzed to define statistical input parameters for fatigue assessment. Finally, a self-organizing-map can visualize the link between local casting process settings and fatigue failure mechanisms. • The defect distribution of fractographic investigations can be well represented by computed tomography taking the largest defects in critical layers into account.