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The Simulation of Internal Stresses of Injection Molded Crystalline Polymers during Cooling Stage

Based on the theoretical analysis about the morphology and the effect of crystallinity on the development of internal stresses for injection molded crystalline polymers, the internal stresses have been simulated by means of a new four elements viscoelastic mechanical model. Considering the crystalline orientation of injection molded parts, the parts are viewed as orthotropic solids to simulate the stresses in both longitudinal and transverse directions. Viewing crystalline polymers as the composites composed of strengthening crystalline phase and softening amorphous phase, the material parameters, such as elastic modulus and viscosity, have been deduced with the rule of mixtures for composites. The results show that internal stresses along the longitudinal direction are obviously larger than the transverse direction in the skin region of the parts. The difference between these two directions decreases in the core region because of the existence of a number of spheric grains.