Solid Element Formulation Using Integral Visco-Elastic Model and Application to Sheet Forming Simulation

Three-dimensional viscoelastic FEM code was developed to simulate thermoforming processes of polymer sheet. The integral constitutive equation known as the K-BKZ model, where the stress is considered the integral of the time domain and some functions, is adopted and the model is newly formulated to solid element. In order to adequately represent the real physical response of polymers, the entire domain history is needed to keep in memory to carry out the integration. A scheme to optimize time step of memory function is proposed. Thermoforming of a circular cup and traveler's case were simulated and compared with the experimental results. The validity of this method is demonstrated by comparing the experimental results.