Along with an increase in the applications of thermoforming to products with more complicated configurations and higher precision, the simulation of this process has become strongly required. In this research, the thermoforming process which consists of blowing, stretching and vacuuming was employed using acrylic-modified PVC sheet. For the achievement of a profitable computer simulation, the employed process was observed in detail. Tne variation of extension ratio in each position of a

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... sheet in successive stages was investigated and the mean strain rate was obtained as nearly 0.1 (1/s). The variation of the temperature of the specimen sheet was measured. Thickness distributions of the sheet after each forming stage was also investigated. Then, an examination of the high-temperature and largestrain behavior of acrylic-modified PVC sheet as a function o£ the forming conditions was performed by uniaxial tensile testing. According to the obtained results by the tensile test, the stress-strain curves depend on the extension rate and especially on the temperature of the specimen. Furthermore, the loading curve is different from the unloading curve and also the deformation generated in the loading can not be recovered completely after the unloading. In conclusion, the visco-plastic behavior and the influence of the sheet temperature must be considered to model the material behavior in the employed thermoforming process for the computer simulation.