黏弹性熔体充模流动诱导残余应力模拟
Simulation of residual stress in viscoelastic mold filling process
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摘要: 流动诱导残余应力是塑料制品产生应力开裂以及翘曲变形等现象的重要原因,对成型过程中流动诱导残余应力研究具有重要意义.推导了基于黏弹性eXtended Pom-Pom本构关系的能量方程,进而建立了描述黏弹性流体非等温充模流动的气一液两相模型.用同位网格有限体积法进行了求解,得到了凝固层和剪切速率分布,给出了充填结束时影响制件力学性能的流动诱导残余应力.结果表明,型腔中凝固层的厚度与注射速率有关,注射速率越大,充模时间越短,凝固层越薄.在制品表层紧邻模壁的地方,剪切速率和残余应力几乎为零;在制品次表层的位置,制件内剪切速率和流动残余应力也较高;而在远离模壁的地方,剪切速率和流动残余应力也较小.Abstract: Flow induced residual stress is the major reason for stress cracking and warping of plastic products, the study on which is significant to overcome the flaws of products. In this paper, the energy equation based on Extended Pom-Pom constitutive relationship is deduced. A non-isothermal viscoelastic-Newtonian two-phase fluid model for mold filling process of viscoelastic materials is set up. The conservative interface capturing technique and the flow field solving method are coupled to perform a dynamic simulation. The distribution of the frozen skin layer and the shear rates are given. The flow induced residual stress is predicted and analyzed. The numerical results show that the thickness of the frozen skin layer is dependent on the injection velocity and a higher injection velocity corresponds to a thin frozen skin layer. Near the walls of the product, the shear rate and the residual stress are almost zero. At the position of subsurface, the shear rate and the residual stress reach their largest values. At the positions far away from the walls of the product, the shear rate and the residual stress are small.
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