Issue 49

A. En-najiet alii, Frattura ed Integrità Strutturale, 49 (2019) 748-762; DOI: 10.3221/IGF-ESIS.49.67 758 As mentioned previously, the rubbery state is owing to the amorphous phase; it is a consequence of the molecular mobility, which allows the chains to be unfolded in the direction of the applied stress, thereby causing deformation. When this constraint is released, it returns to the initial state. A higher cross-linking ratio results in a greater length of the chains between two cross-linking nodes. However, if the nodes of the cross-links are removed, the memory of the initial state disappears, as well as the reversibility of the deformation. In the following, similar to the damage study in the industrial zone, the flow evolution in the thermoforming zone is reported using the same three parameters. In this zone, we define the fraction of life θ for the curves of the stress and Young's modulus, as follows [16]: Ti Tg θ Tc Tg    (6) where: Tg :glass temperature; Tc :critical temperature; and Ti :instantaneous temperature. Moreover, for elongation, we use the following expression for the determination of the fraction of life [16]: Ti Tg θ' 1 Tc Tg     (7)  Adimensional loss of mechanical properties by fraction of life The variation in the ABS mechanical properties as a function of the fraction of life is illustrated in Fig.12. Figure 12: Adimensional loss of ABS mechanical properties in non-industrial zone. The loss of the adimensional stress and Young's modulus increases with the temperature and becomes increasingly important when approaching the thermoforming temperature. However, we note evolution of the adimensional elongation, which appea to indicate that the molecular chains are deformed, and the mechanical behavior of the material resembles that of caotechoutic material. The comparison between the theoretical model (previously defined by Eqn. (3)) and experimental results, illustrated in Fig. 13exhibits strong agreement, which allows us to confirm the effectiveness of the model used in our study for the mechanical behavior of ABS material.