| Transparent injection molded parts have been used widely more and more for its outstanding cost performance. However, residual stresses diminish its utility-properties badly, especially in the mechanical and optical performance. The present study pays close attention to the residual stresses and optical performance of the transparent injection molded parts.In the injection process, residual stresses are caused by complex thermal and mechanical history. It is usually regarded that residual stresses include thermal-induced stress and flow-induced stress, but at present the generation cause, development and interactivity are not completely clear yet. So thermal-induced residual stress and flow-induced residual stress are still calculated separately and then made a simple linear superposition to obtain total residual stresses. The study attempts to research the residual stress distribution and quantification method combined experiments and numerical simulation, in the hope of making some contribution to the engineering practice and theoretical study.Photo-elastic experiment is a kind of effective method without damage for the residual stress measurement of amorphous materials. The residual stress distributions of a series of polycarbonate injection molded plates, from thin to thick, are gained by photo-elastic experiment. It's discovered that when the parts thickness increases, the residual stress distribution shows regular changes:1. When the thickness is less than a certain value, the residual stresses distribute and develop along the flow direction;2. When the thickness is more than another certain value, the residual stresses distribute and develop surrounding inside the part shape;3. When the thickness is between the above two threshold limit values, the foregoing two trends exist together;4. The thickness threshold limit values are related to the injection polymer materials, and then the residual stress distribution shape is determined by the polymer and thickness of the parts.
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