PSI - Issue 42

Guilherme Saldanha et al. / Procedia Structural Integrity 42 (2022) 631–638 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Finally, the endodontic instruments' rotary movement was guaranteed by using a WaveOne ™ control system. This equipment was used to program the rotational speed and the torque applied to the instruments, namely: • Group A - 3 files Hyflex Glidepath 10/.05 | 300 rpm | 1.8 N.cm • Group B - 3 files Hyflex OneFile 25/~ |400 rpm | 2.5 N.cm • Group C - 2 files Hyflex CM 20/.04 | 500 rpm | 2.5 N.cm 2.2. Eddy Currents testing Concerning the non-destructive tests' assessment, a known defect with 0.1 mm in depth and 0.35 mm in width was introduced in a Ni-Ti endodontic file, 5 mm away from its tip (Fig. 3). Moreover, a Ni-Ti wire with a diameter equal to 0.6 mm was used as a reference for the experimental tests and several artificial defects were introduced in 2 regions (Fig. 4), namely: (1) Multiple defects along a 1 mm length, 15 mm from the tip, with the largest being 40 m deep; (2) A single defect, 5.5 mm from the tip, 0.2 mm wide and 100 m deep. Then, two customized types of probes were used to generate the Eddy Currents, namely absolute and differential, made of 10, 15, 20, 25, 30 and 40 coils and subjected to exciting frequencies ranging from 1 to 9 MHz (Fig. 5), while relative motion between the endodontic file (or the wire) and the coils resulted in a scanning speed of 1.2 mm/s. The exciting coils were responsible for generating the primary magnetic field and detecting the secondary magnetic field generated by the Eddy Currents. All windings were close to 2 mm long for both probes, and copper wire with a diamet er equal to 150 μm was used. Generally, the differential type of probe has a better signal-to-noise ratio than the absolute type of probe and is more sensitive to small defects since one section of the material is being compared with the next. The impedance reading of the probes was performed by the Nortec 500D device from Olympus (Fig. 5). This is a commercial equipment developed for performing NDT, which works as an alternating current generator and allows real-time readings of the electrical impedances of the probes. Finally, in addition to the experimental tests, numerical simulations of the eddy current tests were performed using the Ansys Maxwell software.

Fig. 3. Artificial defect introduced in a HyFlex CM instrument, 5 mm away from the tip. (a) Top view, (b) Side view.

Fig. 4. Location and dimensions of the defects introduced in a 0.6 mm diameter NiTi wire..