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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The relative potential P i was calculated from the actual potential U i and the potential of the crack-free specimen U i,0 (mean potential of the first 10 cycles) using equation 1: = ,0 (1) The use of the relative potential P i overcomes the differences in the measured potentials U i caused by small variations of the distance between the measuring contacts and different contact resistance between the specimen and the measuring wires. 3. Results Figure 2 shows the fracture surface of a specimen with a fatigue crack emanating from a secondary notch in form of a laser cut at the position of potential probe 1. The crack expansion was marked by introducing overloads starting from 10,000 cycles in intervals of 5,000 cycles. The size of the fatigue crack was measured along the overload marks using an image analysing program.

Fig. 2. Crack surface with a laser cut at the position of potential probe 1 with overload marks.

Figure 3 shows the change of the 3 relative potentials P i as a function of the relative broken area for several specimens with a single crack initiated at the position of potential probe 1. It is clearly visible that potential 1 increases more than potential 2 and 3, which show nearly the same increase. This clearly indicates that the position of crack initiation has a strong influence on the measured potential drop.