Modeling and numerical simulation of residual stresses and birefringence in injection molded center-gated disks

An appropriate physical modeling and the corresponding numerical analysis system were developed to predict residual stresses and birefringence in injection molded parts such as a center-gated disk. The Leonov constitutive equation is adopted in order to predict flow-induced residual stresses and birefringence. Also the linear viscoelastic and photoviscoelastic constitutive equation taking into account density relaxation phenomena is employed to investigate the thermally induced residual stresses and birefringence. In the preliminary study, constrained quenching was investigated to consider only thermally induced residual stresses and birefringence. Residual stresses are tensile at the center, become compressive near the surface and then return to tensile again at the surface. Flow-induced birefringence has two peaks each of which originated from the filling and packing stages, respectively, and the thermally induced peak has a little flat shape over the whole thickness. Free volume theory was effective in predicting thermally induced residual stresses and birefringence.