PSI - Issue 25

Daniel J. Cruz et al. / Procedia Structural Integrity 25 (2020) 316–323 Daniel J. Cruz et al. / Structural Integrity Procedia 00 (2019) 000–000

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4. Uniaxial Tests on Mini Sample Tester Device - MSTD

Cyclic experimental tests with direction reversal, such as tensile tests followed by compression or vice versa, are fundamental tests for the identification of the mechanical behaviour of metallic materials. To evaluate the MSTD behaviour some cyclic tests were performed. For that purpose, specimens of HC220 sheet with 1.1 mm thickness, and the geometry SS-2x2 mm were tested, Fig. 4b. As in the preliminary tests the Digital Image Correlation technique (DIC) was used to acquire the full-field strain map with the same experimental setup and parameters. As represented in Tab. 3 the test began with a compression loading (step 1) until a maximum force of F max = − 1300 N was reached. At this point, the loading direction was inverted and the specimen began to be loaded in tension (step 2). When the maximum force of F max = 1300 was reached the direction was inverted again and this sequence was repeated (step 3 and step 4). The engineering curve obtained for this sequence is represented in Fig. 8. The material behaviour in the plastic phase is visible both in compression and tension. It is also visible that, during the tests, a plastic accumulation occurs and is responsible for the curve gap. This behaviour is expected and it is due to the type of control used - load control.

Table 3: Test sequence steps performed for HC220 steel Step 1

2

3

4

Designation

Compression

Tension

Compression

Tension to failure

F max [ N ]

F max = − 1300 N

F max = 1300 N

F max = − 1300 N

-

Fig. 8: Results of HC220 compression-tension tests

The strain distribution obtained by Digital Image Correlation is shown in Fig. 9 at the end of compression (step 1) and tension (step 2). It is possible to note that there is a little non-uniformity of the strain in compression. This can be explained by the occurrence of the buckling phenomenon. The strain distribution on step 2 is more uniform. These results indicate that the MSTD is operational and well developed because it was possible to perform tension and compression tests with satisfactory results.