PSI - Issue 54

Naveen Kumar Kanna et al. / Procedia Structural Integrity 54 (2024) 196–203 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 4. Laser notch profile produced with the laser engraving system depicting nearly smooth notch root without any keyholes.

2.2. Mechanical testing and fracture surface analysis The experiments were carried out on a servo hydraulic testing machine with a dynamic loading capacity of ±8 kN. The samples were tested with a base load amplitude of 3-5 kN with a stress ratio of -1 at a frequency of 40 Hz. In order to mark the size and geometry of the cracks on the fracture surface, overloads have been introduced with an amplitude of 8 kN in intervals of 10,000 cycles. The potential drop across the potential probes at the spot-welded grips is measured with the help of amplifiers of the control electronics. The recorded potentials are plotted in Fig. 5 as a function of the loading cycles.

Fig. 5. Recorded potential probe data of the 3 potential probes

Three potential probes are opted to calculate the crack depth a with potential P 1 and crack width c with potentials P 2 and P 3 . However, in the experiments, there were no systematic differences between the potential measured in the center (P 1 ) and the two potentials measured on the outside (P 2 and P 3 ). Therefore, the differences present are due to experimental scatter and a particular potential probe could not be used to determine the crack depth a or the crack width c by the differences in the measured potential values. For this reason, a normalization technique has been considered by taking the relative potential. The relative potential was calculated with Eqn. (3), by dividing the actual potential with the mean value of the first 20 cycles where there was no crack. To reduce the scatter among the measured potentials, a mean value of the 3 relative potentials was calculated and used for further evaluation. = , 0 (3)