PSI - Issue 17

Ekaterina M. Zubova et al. / Procedia Structural Integrity 17 (2019) 822–827 Ekaterina M. Zubova et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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2.2. Experimental procedure

Mechanical tests were performed on an universal electromechanical system Instron 5882 at room temperature and at the rate of 2.0 mm/min. Continuous recording of AE data and waveform data was carried out by using the multi channel AMSY-6 system from Vallen Systeme GmbH. Piezoelectric sensors AE144A (frequency range 100-500 kHz) and preamplifiers (gain 34 dB) were used. The data sampling rate was 10 MHz. The sensors were attached to samples using a Wacker Silicon vacuum silicone grease and rubber bands. The photo of the sample in the grips of the testing machine and sensors' location is shown in Fig. 3.

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AE Sensors

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1 – Instron 5882 system 2 – Vic-3D system 3 – Specimen

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Fig. 3. Experimental set-up with a combined use of the testing and registration equipment (a); location of AE sensors on specimen surface (b).

Registration of inhomogeneous fields of displacements and deformations on the sample surface was carried out using the Vic-3D noncontact three-dimensional digital optical system (Correlated Solutions), whose mathematical apparatus is based on the method of digital image correlation (DIC) [Wildemann et al. (2016)]. Due to the fact that the method of digital image correlation based on the idea of measuring the deformation of the material by tracking the distortion at the pattern of random points on the surface, the sample surface should have a contrasting fine color, which is applied on and the sample before the test. In preparing the surface of the sample, a contrasting fine stain was applied to the surface using white and black matte spray paint. To do this, first applied a white matte base on the surface of the samples, after which a set of black dots was applied. Video shooting was carried out with the help of two digital black and white Q-400 cameras with a resolution of up to 4 Mp, the shooting speed was 15 frames per second. The test system and the AMSY-6 system were synchronized to record the applied load. AE data registration was carried out using a special hardware option that allows squaring and signal integration, as a result of which the signal energy parameter value can be obtained. In this case, the energy parameter is calculated in energy units ( , 1 = 10 − 14 V 2 • ) [AMSY-6 Handbook]. This parameter was described in the works [Wildemann et al (2016), Shilova et al (2014), Tretyakova et al (2019)]. With the help of a special program module, all waveforms were processed and the peak frequency (fast Fourier transform characteristic) were extracted. Peak frequency is a frequency feature reported in kilohertz, which is defined as the point in the power spectrum at which the peak magnitude is observed. [Grosse et al. (2008)]. 2.3. AE data analysis