The effects of melt temperature on the residual stress of thermoplastic polyurethane(TPU)sheets during the injection molding process were studied by birefringence. The results indicate that the residual stress in the near gate area is higher than that in the far gate area and decreases with the increase of the melt temperature. The residual stress of cross section in the two directions is characterized. The injection molded TPU sheets have obvious skin-core structure and zero stress layer. The thickness of core layer increases with the melt temperature rising. The results of residual stress analysis show that the residual stress of core layer is dominated by the flow residual stress, while it is the result of superposition of flow and thermal residual stress in the surface layer. Besides, the warpage deformation is directly related to the distribution of residual stress. The change of the dimensions of the TPU sheets is directly caused by the release of flow residual stress.
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