PSI - Issue 28

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Fatima Majid et al. / Procedia Structural Integrity 28 (2020) 1719–1726 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig.6. Tensile tests curves with different speed loading

3.3. Crack propagation The figure 7 represent the evolution of crack length in function of time for all samples. At the beginning, the crack spreads linearly and the both samples adopt a same behavior. We can see at the figure the evolution of the crack according to the time for the different crosshead speeds. First, we can notice that the crack spreads in a stable way then it accelerates exponentially thus causes a sudden rupture of the specimen 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 that are born around the defect, which results in the decrease of the tenacity of the ABS. Whereas a sample subjected to low loading speed does not break rapidly, it slowly deforms under the action of the mechanical energy provided by the external stresses and the thermal energy due to the molecular motions. Fibrils act as energy absorbers. It can thus be concluded that the rate of loading is a parameter that controls and influences the behavior of amorphous polymers. Depending on the loading speed, the ABS adopts either a ductile or a fragile behavior.

Fig.7. crack length in function of time.