PSI - Issue 37

Jürgen Bär et al. / Procedia Structural Integrity 37 (2022) 336–343 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 1. (a) Positions of the potential probes on the front back and narrow side of the specimen; (b) the wires were spot welded in a distance of y 0 =1.5 mm to the notch root; (c) Location of the potential probes in relation to the fracture surface.

To force a crack initiation at defined positions, secondary notches in form of laser cuts were introduced in the notch root. As shown in figure 2 three different crack initiation sites were investigated: crack initiation in the center, at one edge and at a quarter of the thickness.

Fig. 2. Positions of the secondary laser-notches in the notch root.

For the potential drop measurement, a constant current was conducted through the specimen leading to a potential at the beginning of about U 0 = 0.2 mV. A detailed description of the measurement technology is given by Campagnolo et al (2019) and Hartweg and Bär (2019). For each cycle the maximum and minimum value of the potential was measured. Relative potentials P i were calculated by dividing the actual potential difference U i (with i= front, back and narrow) by the initial voltage U i,0 , defined as the mean value of the potential of the first 20 cycles at the beginning of the experiment (see equation 1). = ,0 ℎ ,0 = 2 1 0 ∙ ∑ 2 =0 1 i = front, back and narrow (1) The relative Potentials were used to determine Quotients by dividing P front and P back by P narrow (equation 2) as suggested in the work of Wiehler and Bär (2020): = and = (2) To compare the real crack geometries with the potential drop measurements the crack surfaces were analyzed by Sem investigations. The marks on the crack surfaces produced by the overloads were colored to enhance the visibility.