Viscoplastic material modeling in the FEM simulation of the thermoforming process of polymer

Elongational deformation is a dominating deformation mode in thermoforming process. Therefore, an accurate material model should be established based on the observation of polymers elongational deformation behavior. However, it is very difficult to find such a research work concerning experiment and modeling of elongational deformation, in a high temperature and high strain rate range, studying combined effect of strain rate, strain hardening, and temperature. Hence, the uniaxial tension tests were conducted for ABS material using the newest type of Meissner rheometer. The tests have been conducted for the constant strain rates varying from 0.01 to 1 (l/s), at the temperatures ranging from 150 degrees C to 200 degrees C. Based on the test data a new material model was proposed. This model could take into account the effects of strain hardening, strain rate sensitivity, variation of the hardening index, and temperature changes. Thermoforming of a square cup, under different initial temperature distribution, was simulated employing the proposed material model and compared with the experiment. The simulated thickness distribution agreed with the experimental data quite well.