PSI - Issue 28

4

Levke Wiehler et al. / Procedia Structural Integrity 28 (2020) 925–932 Author name / Structural Integrity Procedia 00 (2019) 000–000

928

If Q front (Q back ) increases while Q back (Q front ) decreases or remains constant, a crack is initiated near the frontside (backside).

case (a):

case (b): case (c): If both quotients drop, a crack is initiated in the center of the notch. If both quotients rise, cracks are initiated on both sides of the specimen. These criteria can be used to describe the first crack as well as subsequent cracks.

3.2. One-sided crack To be able to make a precise statement about time and location of the crack initiation, the first 30,000 cycles are examined in detail (fig. 3). In sample 1, both quotients initially remain constant until the first overload after 15,000 cycles. At that point, the quotient Q back increases significantly, while the quotient Q front decreases. According to the categorization in figure 2, the first crack is expected near the back of the specimen.

crack

Q front Q back

1.008

1.006

1.004

Q front or Q back

1.002

1.000

0.998

0.996

0.994

0

5,000

10,000 15,000 20,000 25,000 30,000

cycle number

Fig. 3. Run of the quotients Q front and Q back , specimen 1.

Fig. 4. Fracture surface with overload marks and potential probes, specimen 1.