PSI - Issue 56

Cosmin Florin POPA et al. / Procedia Structural Integrity 56 (2024) 176–183 Popa Cosmin-Florin/ Structural Integrity Procedia 00 (2019) 000–000

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The DIC strain measurement on both sides of the specimen also compensates for any twisting or rigid body motion during loading, since the strain values collected on either side are averaged together for the subsequent material property calculations.

3. Results and discussion The purpose of this paper was to observe the difference in behavior between specimens made with contour and those without contour in shear. The first step involved defining the mechanical properties of the PETG material. For this study, the specimens were designed with a contour. Tensile specimens were then manufactured and tested using the same Zwick machine, with a loading rate of 2 mm/min. Figure 3 illustrates the Force-Displacement graph obtained from the tensile testing.

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Without Contour With Contour

Force [N]

Force [N]

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Displacement [mm]

Displacement [mm]

Fig. 3 The Force - Displacement curve at tensile test

Fig. 4 The Force – Displacement curves at shear test

The second step involved conducting shear tests on the Zwick machine. For each specimen, images were captured using DIC. With the help of Instra4D software, the position of maximum shear stress was detected, allowing for a comparison between the strain shape and the experimental values. Once a test was completed, the process was repeated six times for each type of specimen. Fig. 4 shows the Force-Displacement curves for both specimens, the red curve is for the specimen with contour and the blue curve is for the specimen without contour. The difference between curves is about 30% in maximum force. Specimens without contour highlighted a more brittle behavior compared with those with contour. To compute the displacements measured by DIC, two points were fixed on the specimens, Fig. 5. First point 1 was fixed on the upper side of the specimen and the second point 2 was fixed on the bottom side of the specimen. With Instra4D software it was possible to measure the displacement and extract the measurement data. For both specimens, the points were fixed at the same distance. In Fig. 5, the displacements provided by the DIC from the two points near the shear zone are shown. On the graph are overlapped pictures in 3 stages. The pictures were taken in the first step where the force and displacement were 0. The second picture is in an intermediate stage, the value of displacement corresponding to point 1 is 0.38 mm. On the graph, the same picture is around 0.8 mm taken from the machine, and for this, the force is 295 N. The third stage was just before the fracture, the value of displacement is around 1.4 mm (for point 1) and the force is 592 N.