Issue 49

A. En-najiet alii, Frattura ed Integrità Strutturale, 49 (2019) 748-762; DOI: 10.3221/IGF-ESIS.49.67 749 move more freely as the temperature increases. The same damage model was adopted to follow the flow process according to the fraction of life that represents the critical material parameter. This study also includes a comparison between the static (experimental) damage models and unified theory (theoretical) damage models. K EYWORDS . ABS; Damage; Flow; Stress; Reliability; Temperature; Thermomechanical behavior; Tensile testing. I NTRODUCTION he prediction and evaluation of material thermomechanical behavior have long been serious concerns. Thus, numerous models have been developed in to quantify the damage caused by steel materials, with reference to either linear or nonlinear models. Miner (1944) was the first author to formulate a fatigue damage law mathematically, and its linear formulation of the damage as a function of the fraction of the total work absorbed by the material made it a simple and obvious law to use. Other authors, including Quoc et al. (1971), proposed modeling of the damage depending on the loading conditions, stress level, and material characteristics. The models of Henry (1955), Lemaitre and Chaboche (1979), and Gatt (1961) can also be cited as representative damage models. Zgoul and Habali (2008) applied these different theories to steel materials and their alloys. To adapt these theories to polymer materials, we applied these to anacrylonitrile butadiene styrene (ABS) thermoplastic polymer. A substantial amount of research has been conducted on this material to quantify its mechanical behavior. Gonzalo et al (2015) evaluated the effect of the ultrasonic fatigue endurance of polymeric material ABS, and the general mechanisms of crack initiation and propagation, when specimens were tested by being immersed in water and oil, to limit the temperature increase induced by the high mechanical vibration of ultrasonic fatigue testing. Joseph et al. studied the effects of the toxicity of ABS combustion products. Bohatka et al (1995) evaluated the damage formation differences during fatigue crack propagation in ABS polymer, using tests both fulfilling and not fulfilling the linear elastic fracture mechanics requirements, which related to differences in the crack propagation behavior through the crack layer. Boldizar et al. (2003) studied the degradation of ABS during repeated treatments and accelerated aging, whereby the ABS material was subjected to a series of six combined cycles of extrusion and air aging as well as high temperatures, and observed changes in the tensile and flow properties. From the second to the sixth cycle, the elongation at break decreased considerably owing to aging, while it increased as a result of the extrusion step. Shen et al. (1966) and Merah et al. (2003) studied the temperature and weld-line effects on the mechanical properties of chlorinated PVC(CPVC).They investigated the effects of temperatures ranging from -10 to 70°C and injection- molded weld lines on the mechanical properties of CPVC used in pipe fittings. In their studies, they demonstrated that brittle fracture occurred at temperatures below room temperature, while ductile failure occurred at temperatures above 23°C. At temperatures below 50°C, the fracture stress increased in small amounts. A significant increase in the fracture deformity occurred between 50 and 70°C. Plastic deformation at these high temperatures was accompanied by considerable shrinkage. Our work is based on thermomechanical characterization of the material. Several series of tests were carried out in a temperature range of 25 to 170°C, passing through the glass transition temperature (Tg) close to 110°C. For each temperature value, the curves relating to the thermomechanical characteristics such as the stress, elastic modulus, and elongation were plotted to identify the measurements in question for analyzing the material thermomechanical behavior. Thereafter, an extensive analysis of the damage was performed using static damage-reliability modeling. The results of comparing the damage of three parameters, namely the ultimate stress, elastic modulus, and elongation, according to the fraction of life, allowed us to predict the thermomechanical behavior of this polymer in the industrial and thermoforming zones. MATERIAL AND EXPERIMENTAL METHODS he material used in this work was ABS, which is an amorphous polymer produced by emulsification or bulk polymerization of acrylonitrile and styrene in the presence of polybutadiene. T T