PSI - Issue 64

Tahreer M. Fayyad et al. / Procedia Structural Integrity 64 (2024) 708–715 Tahreer M. Fayyad / Structural Integrity Procedia 00 (2019) 000–000

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distribution of colour intensity that is both random and exhibits considerable variation in surface texture, the area under examination on the test specimens was first sprayed with white paint and subsequently with black sparkle glitter spray paint. This variety was intended to furnish each speckle with a distinctive pattern, a critical factor in enhancing the matching accuracy by minimizing the potential for measurement deviation and noise. Fig. 2 (a) displays the sprayed area and includes a magnified view of a region within this area.

Control unit

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LED

Tripod

Camera

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Fig. 2. (a) Test beam; (b) DIC test system The StrainMaster Portable system was used to collect the raw images during testing. The system consists of a device control unit with integrated AD converter, a single-camera and two LED illumination units, all mounted on a tripod, and a laptop computer to run the LaVision software DaVis 10.2. The set up of the system is shown in Fig. 2 (b). The camera was directed toward the middle of the beam where flexural cracks were expected to develop. The obtained spatial resolution differs according to the region of interest and the exact distance between the camera and the surface of the test beam. To transition from pixel measurements to millimetres, an accurately dotted calibration card was employed. This card features a grid of dots arranged with precision. The precision of the dot spacing is claimed to be 1μm. For the purpose of converting pixels in digital images into corresponding metric measurements, the card was positioned on the specimen's surface (Fig. 2 (a)). A second camera was used to capture the behaviour over a wider beam surface ensuring comprehensive data coverage and no missed information regarding the development of other cracks. 2.3. Vibration testing set up Before commencing the damage testing, vibration tests were conducted using rubber hammer testing, where beam dynamic responses due to the hammer tapping were collected to determine beam frequency. As illustrated in Fig. 3, the beam is simply supported and two MEL Data Loggers with a sampling frequency of 512 Hz are used to capture the dynamic accelerations, with Sensor-B located at the 1/4 span, and another Sensor-E located at the 1/2 span. Fig. 3(b) also outlines the sensor layout for damaged beam.

(a) (b) Fig. 3. (a) Healthy beam testing; (b) Damaged beam testing