Issue 49

A. En-najiet alii, Frattura ed Integrità Strutturale, 49 (2019) 748-762; DOI: 10.3221/IGF-ESIS.49.67 757 mechanical behavior of the components. In this section, we present a reliability study to reduce the probability of sudden failure. The reliability R is a statistical parameter, which follows the evolution of the material deterioration. The relationship between these two parameters can be expressed as follows: R (β) + D (β) = 1 (5) [21]. Using Eqn. (5) to plot the different reliability curves corresponding to the various parameters studied, the following figures illustrate the variations in the reliability and damage as a function of the fraction of life in the industrial zone. We note that the damage always evolves in the opposite direction to the reliability as the temperature increases. Figure 11: Evolution of damageand reliability as function of fraction of life . The present work provides the opportunity to discuss the mechanical behavior of a well-known polymer that is extensively used in industrial areas; specifically, in the manufacture of cars. To facilitate quality control without the need for an expensive dynamic test, we conducted a study to compare the mechanical characteristics with the aid of elevated temperature tensile testing. The analysis of the static and thermic tests allowed us to evaluate the negative effects of the increase in temperature on the ABS mechanical behavior more significantly. Indeed, the curves in Fig. 11illustrate that the stress and Young's modulus parameters exhibit comparable damage, regardless of the fraction of life. To overcome the challenges of dynamic tests, we modified the unified theory controlled by elongation, to consider a new parameter relating to the mobility of molecules and the constriction of material. Although the results obtained from the three parameters are in harmony, the use of elongation remains less precise and exhibits a phase shift compared to the other parameters (Young's modulus and stress). Thermomechanical behavior of ABS material in thermoforming zone (non-industrial zone, T>Tg) The degradation of the mechanical properties is always remarkable. The elastic stress, ultimate stress, tensile strength, and elasticity decrease more significantly as the temperature increases, and the material begins to deform permanently. The intrinsic softening zone corresponds to the beginning of the nonlinear distortion (this softening of the plastic flow threshold is mainly owing to the change in the material microscopic structure), and this deformation continues with a remarkable increase in temperature. Thereafter, it falls towards the point at which it stabilizes and remains constant with an increasing elongation. The plastic deformation is owing to the material rubbery state, and this deformation is localized on the section of the sample in a region known as the curing zone. The rubbery state is a result of the amorphous phase, and exists in practically all polymers; it generally begins around the glass transition temperature and is limited by the melting temperature or thermal decomposition temperature. In the amorphous phase, the molecular organization is constantly changed by displacement of the molecules, owing to thermal activation or the applied stress (constraint). This state change with respect to the vitreous state described above is accompanied by rupturing of certain weak bonds (Van der Waals) between molecules by means of thermal agitation, and a significant increase in the polymer volume. This results in greater ease of movement of the molecules, so that the very low molecular mobility in the vitreous state increases with an increasing temperature.