PSI - Issue 13

Kiiko V.M. et al. / Procedia Structural Integrity 13 (2018) 1433–1437 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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2. Experimental setup

We set up the problem for determining the equipotential line geometry in a sample without a crack and a sample with a lateral crack. The specimen is simulated with electrically conductive paper. We apply an electric voltage to the flat sample along the ends, and an electric current passes through it (Fig. 1). We establish a picture of the equipotential line distribution as follows. Two wires with probes are connected to a voltmeter. One probe is fixed at the desired point (e.g., at the edge of the sample), and the other probe is moved along the surface of the sample, starting from the stationary probe such that the voltage between the probes is zero. The trajectory of the moving probe gives an equipotential line (Fig.1). A crack is modeled by a cut in the paper. We show the results of two variants of a crack-cut in Figs. 1b and 1c.

a c Fig. 1. Equipotential lines in a specimen when passing an electric current through the specimen vertically: (a) without a crack, (b) with a side crack, and (c) with a central crack. We consider a flat electrically conductive sample containing a side crack (Fig. 2a). In the vicinity of the crack, we select a point M where the fixed probe is placed. Moving the other probe along the edge of the sample, we find a contact point N where the voltage between the points M and N is zero as indicated by the voltmeter attached to the probes. The points M and N are then on one equipotential line. b

a b Fig. 2. (a) Schematic of converting the growth Δ l = l 2 - l 1 of the crack length l in a shift Δ x of the movable contact and (b) a technical realization. V is a voltmeter, I is an electric current, A and B are electrical contacts.