PSI - Issue 28

Najat Zekriti et al. / Procedia Structural Integrity 28 (2020) 1745–1754 Najat Zekriti and al/ Structural Integrity Procedia 00 (2019) 000–000

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3.2. The effect of loading speed To identify the influence of the strain rate on crack propagation velocity, we carried out a series of tensile tests on the both of our samples extruded and printed with different speed loading as shown in following figures. a. b.

Fig.5. Tensile tests curves with different speed loading (a) extruded ABS; (b) printed ABS

To identify the behavior of different samples extruded and printed, we measure the variation of crack length in function of time. A digital camera carries out the measurement optically. Fig.6.

Fig.6. Variation of crack length in function of time.

The previous figure shows the evolution of the crack according to the time. Both ABS have almost the same appearance, as we can notice that the crack spreads in a stable way then it accelerates exponentially thus causes a sudden rupture of the specimens. However, the extruded samples are more fragile than the printed ones that take more time to break. Therefore, we can say that the printed ABS is less fragile due to the filament orientation. . The ABS is approaching a completely fragile behavior at high speeds. Indeed, when the loading speed is high, the surfaces of craze quickly move away, which justifies the sudden rupture of the ABS. The macromolecular chains do not have enough time to reorient themselves within the crazes. Thus, the fibrils bridging the many cracks break because of the micro voids born around the defect, which results in the decrease of the tenacity of the ABS.