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Numerical simulation of the heating stage of thermoplastics in thermoforming requires a good knowledge of the behavior of the materials used. To this end, a study is being conducted on the characterization of the viscoelastic behavior of a circular membrane, made of high-density polyethylene (HDPE), under the combined effect of temperature and the force of gravity. The experimental tests were carried out in a convection oven for five temperatures (100, 110, 120, 130 and 140 C). For the numerical characterization of the viscoelastic behavior, two viscoelastic models were considered: the classic Kelvin-Voigt model and the new three-parameter modified Burger's model (Jeffrey model) that we propose. The mechanical parameters of both models were identified using the Levenberg-Marquardt algorithm. The thermal-dependency of the viscosity was characterized by two thermal models: the Arrhenius law and the William-Landel-Ferry (WLF) equation.

Stress behaviour of the vehicle suspension system has received much attention in recent years due to its effect on life time of different parts, especially lower suspension arm. These stresses can be reduced by optimizing and design variables of automotive lower arm suspension system as well as its materials metallurgical parameters. The high strength-to-weight ratio of aluminium casting alloys makes them materials of choice. The studied model is selected to be close to real operation of automotive suspension system. The main objectives of this study are to propose the proper variables required in design of suspension system parts and to reduce the stresses on lower arm-suspension system by materials and design optimum selection. The agreement of the vibration model of vehicle, design variables for optimization and the materials selection validates its positive effect on the mechanical and quality performance of applied parts made of aluminium alloys.

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