Mechanical Testing and Material Modeling of Thermoplastics: Polycarbonate, Polypropylene and Acrylonitrile-Butadiene-Sty
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Mechanical Testing and Material Modeling of Thermoplastics: Polycarbonate, Polypropylene and Acrylonitrile-Butadiene-Styrene J.L. Bouvard, H.R. Brown, E.B. Marin, P. Wang, and M.F. Horstemeyer Center for Advance Vehicular Systems (CAVS) Mississippi State University, Mississippi State, MS 39762, U.S.A. ABSTRACT The work presents some results of an ongoing research program aimed at building a material database and material models for specific types of polymers. Results for three thermoplastics are the focus of the present article: polycarbonate, polypropylene, and acrylonitrile-butadiene-styrene. Uniaxial compression / tension tests at room temperature and different strain rates have been performed to characterize their mechanical response. A ratedependent material model has been developed and implemented in a finite element code to predict such mechanical behavior. The model predictions have shown good agreement with the tests results. INTRODUCTION The automotive industry is currently interested in using lighter and impact resistance materials in vehicular systems, as they would make vehicles more fuel efficient without compromising safety standards. In this context, polymeric materials are a good option for this application. In fact, currently polymers represent 20% of the total weight of a car, with thermoplastics and thermosets being about 10% to 15% of this weight. Based on these statistics, it has been found that by substituting 10lb of other materials using polymers, the fuel efficiency can be improved by 0.11 to 0.14%, an important aspect that makes polymers a material of choice in the automotive industry [1]. In the present study, mechanical characterization tests were performed on three thermoplastics largely used in the automotive industry. The goal was to capture their structureproperty relationships under different loading conditions. The particular results (stress-strain curves) presented here were obtained at room temperature and at low to medium strain rates. Also, material modeling efforts were started to capture the experimentally determined mechanical behavior. The current material model used an internal state variable formalism, and followed closely a widely used theory for amorphous polymers [2] but framed in a thermodynamic setting [3]. The model was implemented in the finite element code ABAQUS and applied to predict the strain-rate dependent response of the three thermoplastics. EXPERIMENTAL PROCEDURE The three thermoplastics selected for the study are: (i) an amorphous polycarbonate (PC) known under the trade name Hyzod from Sheffield Plastics, (ii) an isotactic polypropylene (PP) provided by Poly Hi Solidur Inc., (iii) a copolymer acrylonitrile butadiene styrene (ABS) supplied by King Plastic Corp. The compressive and tensile specimens were cut from sheets of 1” thickness.
Low and medium strain rate tests were conducted at room temperature (RT) on an INSTRON 5882 electro-mechanical load frame machine. The tests were strain-controlled, with the strain measurements being perform
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