PSI - Issue 25

Daniel J. Cruz et al. / Procedia Structural Integrity 25 (2020) 316–323

318

Daniel J. Cruz et al. / Structural Integrity Procedia 00 (2019) 000–000

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In this study, a new mini-tensile approach was developed to perform tensile tests on miniature specimens, which include Digital Image Correlation technique to visualise the strain pattern. This paper is organised as follows: first, a series of preliminary tensile tests are shown using di ff erent types of miniaturised geometrie; second, a new mini tensile equipment is exhibited to perform uniaxial tests in sheet metal; finally, some results of tension-compression tests are presented.

2. Preliminary Tensile Tests

In order to verify the accuracy when using miniaturised specimens, a series of preliminary tensile tests were per formed. A prototype, Fig. 3a, was used with developed specimen geometry on a mesoscale. The sheet metal material used for this study was a magnesium AZ31B with 0.6 mm thickness. For mini-tensile tests, dimensions and geome tries are not yet standardized and they vary according to di ff erent authors. Thus, in these tests, two types of geometries were chosen: the first with a width of 2 mm and a uniform length of 12 mm (SS-2x12 mm) - Fig. 4a; the second with the same width but with a smaller length (SS-2x2 mm) - Fig. 4b. The manufacturing process chosen to obtain the geometry of specimens was milling process. To evaluate the accuracy and repeatability three specimens were tested, for each geometry, The tests were performed at room temperature, with a crosshead speed capable of achieving a strain rate of about 10 − 3 s − 1 in both types of geometry.

(b)

(a)

Fig. 3: Experimental setup used in the preliminary tensile tests

(b) SS-2X2

(a) SS-2X12

Fig. 4: Di ff erent types of geometry used in the preliminary tests; all units are in [mm]

Digital Image correlation (DIC) technique has been used to acquire the full field strain map of the miniature samples. To improve the accuracy of the image correlation, high contrast speckle pattern with the average size of 5 pixel per speckle was applied. Images were recorded using a Point Grey Gazelle 4.1 MP Mono Camera with Rodagon 80 lens. Samples were illuminated using a combination of a 250W spotlight and a LED flashlight. Post-processing of the images was performed via VIC-2D from Correlated Solutions. The camera setup and post-processing parameters are included in the Tab. 1.