新型热塑性复合材料的结构设计及制造过程的数值模拟

发布时间：2018-04-03 16:35

本文选题：复合材料　切入点：结构　出处：《华东理工大学》2017年博士论文

【摘要】：聚合物基复合材料的结构设计和制造技术是目前关注的两大主要方向。本文通过不同的工艺制备了两种新型的热塑性复合材料,并对他们的结构-性能关系进行研究,以满足对汽车复合材料轻质高强的需求。同时本文将数值模拟技术应用到热塑性复合材料的制造过程,对双钢带压机的传热和浸渍两大工程问题进行了研究。本文分别采用预混粉体浸渍工艺和在线混合工艺制备长纤维增强热塑性复合材料(LFT),并与单向连续纤维带(EF)层合,最终得到E-LFT,并研究其多尺度结构对力学性能的影响。在宏观上,EF层对强度、模量以及韧性的贡献不同,对韧性的贡献最大;在微观上,纤维长度的增加有利于E-LFT力学性能的提高,而分布的纤维长度优于均一的纤维长度;介观上,纤维束能够起到增韧的作用。E-LFT能够在保证强度和刚度的基础上,大幅提高韧性,而分层破坏是高韧性的重要原因。然后通过对比不同的增强体分布形式对力学性能的影响,探讨层合及分布对热塑性复合材料的意义。层合过程不仅比传统混杂容易,而且能够充分体现复合材料的可设计性。本文分别采用薄膜浸渍和混合纤维两种浸渍工艺制备GMT实心坯料,经过充分膨化和有限压缩得到LWRT,并研究其多相结构对力学性能的影响。其中孔隙率对LWRT力学性能的影响很大,它可以通过面密度和厚度进行调控。必须有足够的纤维长度才能提供较高的力学性能。界面对LWRT的力学性能影响非常显著,相容剂的加入不仅提高了纤维和基体的界面剪切强度,而且提高了基体在纤维表面的分散性,这可以通过界面自由能理论解释。本文对双钢带压机中的传热过程进行了数值计算。采用离散坐标(DO)模型模拟红外加热管对钢带的预热过程,得到钢带的升温曲线,并研究了加热系统的结构对辐射传热的影响,其中包括红外加热管的位置、直径和数量、保温层的厚度、钢带和辊筒的接触热阻,最终得到优化的结构。除了辐射作用,空气的自然对流也会对钢带的预热产生影响。物料层中的相变传热则是双钢带压机中的另一个重要问题。考虑相变潜热的基础上,模拟物料在双钢带压机运行过程中的传热过程,并得到钢带运行速度对预热和冷却过程的影响,最终选择合适的钢带运行速度。本文又通过CFD模拟了纤维织物代表体积单元的浸渍过程。结合有限体积法和VOF方法对气-液两相界面进行追踪,求解多孔介质两相流问题。该方法能够清晰地捕捉到气泡的形成和排除,获得树脂体积分数随时间的变化,从而预估完成浸渍所需的时间。本文考察了压力、粘度以及纤维束孔隙率等参数对浸渍速率的影响。
[Abstract]:The structure design and manufacturing technology of polymer matrix composites are two main directions of attention.At the same time, the numerical simulation technology is applied to the manufacturing process of thermoplastic composite material, and the heat transfer and impregnation of double steel strip press are studied.In macroscopically, the contribution of EF layer to strength, modulus and toughness is different, but the increase of fiber length is beneficial to the improvement of mechanical properties of E-LFT, while the distributed fiber length is better than that of homogeneous fiber length.Then the significance of lamination and distribution to thermoplastic composites is discussed by comparing the effect of different reinforcement distribution on mechanical properties.The lamination process is not only easier than the traditional hybrid process, but also can fully reflect the design of composite materials.In this paper, GMT solid billets were prepared by film impregnation and mixed fiber impregnation, and the effects of multiphase structure on mechanical properties were studied.The porosity has a great influence on the mechanical properties of LWRT, which can be controlled by surface density and thickness.Sufficient fiber length is required to provide higher mechanical properties.The influence of interface on the mechanical properties of LWRT is very significant. The addition of compatibilizer not only improves the interfacial shear strength of fiber and matrix, but also improves the dispersion of matrix on the surface of fiber, which can be explained by the theory of interfacial free energy.In this paper, the heat transfer process in double steel strip press is numerically calculated.The preheating process of infrared heating tube to steel strip was simulated by using discrete coordinate DOA model, and the heating curve was obtained. The influence of heating system structure on radiation heat transfer was studied, including the position, diameter and quantity of infrared heating pipe.The thickness of the insulation layer, the contact thermal resistance between the steel strip and the roller is finally optimized.In addition to radiation, the natural convection of air also affects the preheating of the strip.Phase change heat transfer in material layer is another important problem in double steel strip press.Considering the latent heat of phase change, the heat transfer process of the material in the operation of the double strip press is simulated, and the influence of the running speed of the strip on the preheating and cooling process is obtained. Finally, the suitable running speed of the strip is selected.In this paper, the impregnation process of fiber fabric representing volume unit is simulated by CFD.The gas-liquid two-phase interface was traced by the finite volume method and VOF method to solve the two-phase flow problem in porous media.This method can clearly capture the formation and removal of bubbles and obtain the change of resin volume fraction with time, thus predicting the time required to complete the impregnation.The effects of pressure, viscosity and fiber bundle porosity on the impregnation rate were investigated.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB332

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