Bulk viscosity describes the irreversible resistance to the rate of volume change. Bulk viscosity, which is more than ten thousand times higher than shear viscosity, has been ignored in the field of polymer processing for the past decades. Bulk viscosity may play an important role for compressible polymer melts undergoing strong compression during processing, especially during the packing and holding stage in injection molding. In this study, bulk viscosity of an amorphous Polystyrene melt is investigated through measurements, modeling, and implementation in an injection molding simulation. The results demonstrated that bulk viscosity can be derived from a cooling rate-controlled PVT (pressure-specific volume–temperature) measurement. A new pressure-specific volume–temperature–cooling rate model was developed to obtain smooth and reliable bulk viscosity results. Furthermore, a Cross-William–Landel–Ferry–Arrhenius model was found capable of describing the dependence of temperature, rate of volume change, and mechanical pressure on bulk viscosity of this polymer melt. The proposed modeling was first verified using the non-equilibrium PVT and then was implemented into an injection molding simulation. Simulation results showed that the effects of bulk viscosity not only prevent the material from changing its size but also reduce mechanical pressure variations during the injection molding packing stage.

中文翻译：

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聚苯乙烯熔体体积粘度的测量和建模

体积粘度描述了对体积变化率的不可逆阻力。体积粘度比剪切粘度高一万多倍，在过去的几十年里，在聚合物加工领域一直被忽视。体积粘度对于在加工过程中经受强烈压缩的可压缩聚合物熔体可能起着重要作用，尤其是在注塑成型的保压和保压阶段。在这项研究中，通过测量、建模和在注塑模拟中的实施来研究无定形聚苯乙烯熔体的体积粘度。结果表明，体积粘度可以从冷却速率控制的 PVT（压力比体积 - 温度）测量中得出。开发了一种新的压力比体积-温度-冷却速率模型，以获得平稳可靠的体积粘度结果。此外，发现 Cross-William-Landel-Ferry-Arrhenius 模型能够描述温度、体积变化率和机械压力对这种聚合物熔体的体积粘度的依赖性。建议的建模首先使用非平衡 PVT 进行验证，然后实施到注塑成型模拟中。模拟结果表明，体积粘度的影响不仅可以防止材料改变其尺寸，还可以减少注射成型保压阶段的机械压力变化。以及对该聚合物熔体的体积粘度施加机械压力。建议的建模首先使用非平衡 PVT 进行验证，然后实施到注塑成型模拟中。模拟结果表明，体积粘度的影响不仅可以防止材料改变其尺寸，还可以减少注射成型保压阶段的机械压力变化。以及对该聚合物熔体的体积粘度施加机械压力。建议的建模首先使用非平衡 PVT 进行验证，然后实施到注塑成型模拟中。模拟结果表明，体积粘度的影响不仅可以防止材料改变其尺寸，还可以减少注射成型保压阶段的机械压力变化。