PSI - Issue 17

Moritz Hartweg et al. / Procedia Structural Integrity 17 (2019) 254–261 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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a

b

Fig. 6. Run of the calculated angle (a) and corresponding specimen (b).

In case of multiple crack initiation sites, the calculated angle can give no information about the position of the individual cracks. The resulting angle gives just an information about the main emphasis of the summarized area of all initiated cracks. In figure 7a the run of the calculated angle smoothed with a gliding average over 10 points for the specimen shown in figure 7b is shown. The specimen shows 7 individual cracks and the run of the angle exhibits a constant value of about 150° between 20,000 and 80,000 cycles, showing that obviously the two cracks in the lower right are dominating in this period. After that the angle decreases, indicating that additional cracks are formed and become dominant.

a

b

Fig. 7. Run of the calculated angle and fracture surface of a specimen with multiple crack initiation sites.

The scatter of the calculated angle is also decreasing with the cycle number (figure 7a). Obviously, the reduction of the scatter indicates the formation and propagation of cracks, even in specimens with multiple cracks. Starting from about 80,000 cycles a continuous decrease of the scatter due to crack propagation can be observed. The strong decrease of the scatter in the first 10,000 cycles maybe attributed to an early crack initiation. In that case, the following period