PSI - Issue 28

Michael Jones et al. / Procedia Structural Integrity 28 (2020) 2078–2085 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2.2. Test Setup and Procedure A novel method was used to acquire data from the multiaxial tensile tests, based on the work of Sancho et al. (2019). This involved image capture of the specimen to determine the edge profile of the specimen as it deformed. The test setup is illustrated in Figure 2. Tests were carried out in a furnace so that the specimen could be kept at a temperature of 550°C throughout. Images were captured using a Nikon D7200 and 200 mm f/4D lens positioned in front of the furnace window. In order to obtain accurate results, it was necessary to produce strong contrast between the specimen and the background so that the edges were clearly defined in the image. To aid this, a sheet of metal sprayed white was positioned behind the sample. The outer surface of the specimen naturally tinted and darkened in colour due to the oxidation at high temperature. The combination of these two effects yielded the necessary level of contrast.

Figure 2 – Illustration of test setup with camera positioned to acquire images of the specimen cross section.

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Figure 3(a)-(b) – An example of an image (a) taken directly by the camera, (b) postprocessed using darktable to improve contrast and (c) thresholded for analysis.