Thèse de doctorat en Sciences des matériaux industriels
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Experimental study and modeling of flow of thermoplastics composites in industrial conditions of injection molding
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In view of the research performance materials and industrial process control processing, this work is the experimental study and modeling of the flow of thermoplastic composites in industrial layout by injection. The first part deals with experimental study in industrial conditions formatting injection of rheological behavior and the study of flow in simple geometries, polypropylene composites reinforced with short glass fibers. At first we highlighted the influence of thermomechanical processing parameters by injection on the viscosity and elasticity of different materials using a rheometer online. These tests showed that the viscosity of composites in the molten state evolved, in a non-linear, depending on temperature, shear rate and the rate of fiber. This part is complemented by an analysis of pressure losses in non-isothermal conditions. Furthermore, results of rheological measurements have been used to determine a thermodependent rheological behavior law of the composite at different rates of fiber. This law has been used to simulate the filling phase of the mold cavity during the cycle of injection molding. In the second part, we present an experimental study both qualitative and quantitative distribution and orientation of fibers during different phases of injection molding. We conducted an experimental study of the distribution of lengths of fibers during the plasticizing phase. This work allowed us to highlight the impact of certain parameters for adjusting the press on fibers break and locate critical location of fiber degradation. Then we conducted a thorough experimental study of the distribution and orientation of fibers in injected plates, depending on the conditions of injection, the composition of the composite material and the geometry of the part. We have demonstrated the presence in the thickness of the plate, a structure "core-skin" to five layers with a central layer oriented transversely to the direction of flow, two intermediate layers mainly oriented in the direction flow and finally two layers of skin slightly less oriented than the intermediate layers. The thicknesses of these layers vary depending on injection conditions (temperature, speed). The last part of this work is devoted numerical simulation of the filling phase of the process of injection molding of composites PP / VF, based on a law deduced from rheological experiments. We are particularly interested in predicting the orientation of short glass fibers in a rectangular plate injected, depending on injection conditions (temperature, pressure and speed), on the polymer composition and on geometry of the part. On the other hand, we have highlighted the influence of injection parameters on the evolution of pressure, temperature and the average velocity in the mold cavity. The simulation results are compared with experimental measurements.