PSI - Issue 41

R. Nobile et al. / Procedia Structural Integrity 41 (2022) 421–429 Riccardo Nobile et al. / Structural Integrity Procedia 00 (2019) 000 – 000

423

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Table 1. Mechanical properties of AISI 316L austenitic stainless steel. (0.2%) Yield Stress σ y [MPa] Young’s modulus E [GPa]

Ultimate tensile strength σ u [MPa]

Poisson’s ratio ν

170

485

0.3

193

The experimental equipment adopted for the real-time monitoring fatigue tests includes a power supply generator and a digital acquisition data unit Agilent model 34970(Fig. 2), which has 6 ½ digits (22 bits) of resolution and a basic accuracy of 0.004 % with extremely low reading noise. In addition, three thermocouples T-type were applied in the center of the net section and in correspondence of the two notch tips. For the tests, insulating tabs were built and glued to the ends of the specimen to ensure perfect isolation of the specimen from the testing system.

(a) (b) Fig. 2. (a) Specimen with electrical contacts and location of the three T thermocouples; (b) experimental setup of fatigue monitoring by ERC measurements on the specimens AISI 316L. To measure the electrical resistance, a direct current of 3000 mA was injected through two external electrodes into the specimen, while the resistance is determined by measuring the voltage drop between two internal electrodes in the typical four-wire configuration. The electrodes used in this research consist of conductive copper adhesive tape. Figure 3a-b shows the positioning of the electrodes and the circuit used for measuring the electrical resistance of the specimen, in which the resistances R 1 , R 2 , R 3 and R 4 are the parasitic resistances due to wires and electrical contact, while R sp is the resistance of the specimen detected between the internal measuring electrodes.

(a) (b) Fig. 3. (a) Contacts scheme: four-electrode configuration and location (TC: thermocouples); (b) circuit for measuring electrical resistance.