长纤维增强聚合物的轻量化设计. 由于纤维基体分离的影响而带来的技术挑战
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- 毕设文献翻译全球汽车制造商的目标是减轻汽车的重量，因为由于消费者需求和政府规定，更多的电器、功能和安全特性被整合在一起。随着电动火车、全电动汽车或混合动力汽车的增加，电池的重量显著增加了汽车的总重量。未来汽车的目标是减轻重量，以实现更严格的碳排放法规[1-3] ，同时仍保持良好的性能。纤维增强聚合物(FRP)为大规模生产提供了较高的机械性能和较低的成本。通过与其他轻质材料的智能结合，FRP 使未来轻质设计成为可能。
Virtual process simulation tools for processing of discontinuous FRP minimize unnecessary process steps during component design and evaluation. Commercially available simulation tools are used to model numerous effects during processing. In the field of fiber reinforced polymers, the resulting fiber parameters (orientation, length, content) inside the composite are of great value, especially for the use in structural and safety-related components. By using the predicted fiber parameters in the process simulation, the component behavior can be precisely simulated for multiple scenarios, such as crash and fatigue. Current simulation tools have multiple models available for the prediction of fiber orientation [4] and fiber length degradation [5]. With increasing fiber length, a non-uniform fiber density distribution appears throughout the component. Current simulation tools do not adequately represent this phenomenon.
不连续 FRP 加工的虚拟过程模拟工具，最大限度地减少了零件设计和评估过程中不必要的加工步骤。商业上可用的模拟工具被用来模拟加工过程中的许多效果。在纤维增强聚合物领域，由此得到的纤维参数(取向、长度、含量)在复合材料中具有重要的价值，特别是在结构和安全相关部件中的应用。通过在过程模拟中使用预测的纤维参数，可以精确地模拟多种情况下的组件行为，如碰撞和疲劳。目前的模拟工具具有多种模型可用于预测纤维取向[4]和纤维长度退化[5]。随着纤维长度的增加，整个组件中出现不均匀的纤维密度分布。目前的模拟工具并不能充分代表这种现象。
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The effect of FMS has been mentioned in earlier publications [7-8], but it is not thoroughly examined to date. Fiber content experiments with BMC by Schmachtenberg et al. [7] show an increase in fiber content over a flow path in relation to the processing parameters. Experiments with Londoño et al. [8] show a significant change in fiber content in a breaker box. Londoño gives a first introduction to complex forces working at the rib geometry and the principle of the complex interaction between fibers and matrix. He describes the two governing forces during mold filling of rib geometries. According to Londoño, the fibers are squeezed into the rib according to Darcy’s Law (Eq.1), which describes the flow of a fluid through a porous medium in relation to the fluid velocity (V), the porosity (κ), viscosity (η) and the pressure gradient (dp/dx). Bakharev and Tucker [9] predict the permeability of a glass fiber bed (Eq.2).
FMS 的效果在早期的出版物[7-8]中已经提到，但迄今为止尚未彻底检查。Schmachtenberg 等[7]用 BMC 进行的纤维含量实验表明，与加工参数相比，在流动路径上纤维含量增加。Londoño 等人的实验[8]显示断路器箱中纤维含量的显着变化。Londoño 首次介绍了在肋骨几何形状上工作的复杂力以及纤维和基质之间复杂相互作用的原理。他描述了肋骨几何形状充模过程中的两种控制力。根据 Londoño 的理论，纤维根据达西定律(Eq. 1)挤入肋骨，达西定律描述了流体在多孔介质中的流动与流体速度(v)、孔隙度(κ)、粘度(η)和气压梯度(dp/dx)的关系。Bakharev 和 Tucker [9]预测了玻璃纤维床的渗透率(Eq. 2)。
(1) (2)
(1)(2)
The hydrodynamic force on the fiber at the rib entrance can then be calculated as the pressure on
在肋骨入口处的纤维上的流体动力可以计算为
the effective fiber area, as described in Londoño et a. (3), where is the closing speed of the press, Lrib the width of the rib and L the length of the fiber bundle.
有效纤维面积，如 Londoño 等(3)中所描述的，这里是压力机的闭合速度，Lrib 是肋骨的宽度，l 是纤维束的长度。
(3)
(3)
According to Londoño et al. [8], the force counteracting the fibers getting squeezed into the rib geometry is represented by the force (F) needed to bend fibers into the rib (Eq. 4), where (Cf) is a constant, (E) the Young’s modulus, (EI) the moment of inertia, (δ) the deflection of the fiber and (Lr) the free length of deflection.
根据 Londoño 等[8]的理论，抵消纤维挤入肋骨几何形状的力可用将纤维弯入肋骨所需的力(f)表示(Eq)。4) ，其中(Cf)为常数，(e)杨氏模量，(EI)转动惯量，(δ)光纤的挠度，(Lr)自由挠度长度。
(4)
(4)
Londoño introduces a Fiber-Matrix Separation constant Θ, which describes the ratio of fiber deflection force to hydrodynamic foces (Eq. 5). FMS occurs for values of Θ << 1, when the fiber bending forces are higher than the hydrodynamic forces and the matrix is squeezed out of the fiber bed.
Londoño 引入了纤维矩阵分离常数 θ，描述了纤维偏转力与流体力学力的比值(Eq)。5).当纤维弯曲力大于流体力学力，基体被挤出纤维床层时，当 θ < 1时，发生 FMS。
(5)
(5)
A suggested continuum model describes the interaction of the fibers and the polymer matrix as a two phase flow (Figure 1). Hereby, the fibers and the polymer matrix are divided into two separate domains, which are displayed as an elastic fiber domain (grey, velocity vector v) and a viscous polymer matrix domain (red, velocity vector u). These two domains interact as described in the Fiber Matrix Separation constant. The ratio of elastic fiber forces to viscous hydrodynamic forces Θ describes the differences in flow of the two phases. A simplified description of the counteracting forces is shown in Figure 2 . During Fiber Matrix Separation, the elastic fiber forces excel the hydrodynamic forces, leading to a reduced fiber content in the flow front and an agglomeration along the flow path.
建议的连续介质模型描述了纤维和聚合物基体作为两相流的相互作用(图1)。在此基础上，将纤维和聚合物基体分为两个独立的区域，分别表示为弹性纤维区域(灰色，速度矢量 v)和粘性聚合物基体区域(红色，速度矢量 u)。这两个域如纤维矩阵分离常数中所述相互作用。弹性纤维力与粘性流体力的比值 θ 描述了两相流动的差异。反作用力的简化描述如图2所示。在纤维基体分离过程中，弹性纤维受力大于水动力，导致流动前沿纤维含量降低，沿流动路径形成团聚。
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Figure 1: A continuum model of a two phase flow of matrix (red) and fiber phase (grey)
图1: 基质(红色)和纤维相(灰色)两相流动的连续模型
Figure 2: Interaction of the elastic fiber and viscous matrix domain in a continuum model for Fiber Matrix Separation
图2: 纤维基质分离连续模型中弹性纤维和粘性基质域的相互作用
In this paper, the effect of Fiber Matrix Separation is examined in compression molding experiments with long glass fiber reinforced thermoplastic materials. The selected mold geometry features a series of different ribs with alternating design. The effect of differing material properties and rib designs on Fiber Matrix Separation is analyzed. In this context, the fiber properties are measured using traditional processes like pyrolysis as well as state of the art CT imaging. The gathered data is then analyzed and compared to the process simulation results.
本文在长玻璃纤维增强热塑性材料的压缩成型实验中，考察了纤维基体分离的影响。所选择的模具几何形状具有一系列不同的肋骨与交替设计。分析了不同材料特性和肋条设计对纤维基体分离的影响。在这种情况下，纤维性能的测量使用传统的过程，如热解以及国家最先进的 CT 成像。然后分析收集的数据并将其与过程模拟结果进行比较。
Material
材料
Compression molding experiments were performed with glass mat thermoplastic sheets (GMT) supplied by Quadrant, Lenzburg, Switzerland. GMT is manufactured by impregnating a needled glass mat with thermoplastic resin in a belt press. The advantage of GMT is the high achievable fiber length in the final part. In comparison to other LFTs, the GMT is not extruded prior to the compression molding, hence fiber damage and attrition is reduced. In order to analyze the influence of fiber properties during processing, GMT materials with varying fiber contents and fiber lengths are used. An overview of the used materials is given in Table I.
采用瑞士伦茨堡 Quadrant 公司提供的玻璃垫热塑性薄板(GMT)进行了压缩成型实验。GMT 是通过在带式压力机中用热塑性树脂浸渍针状玻璃垫而制造的。GMT 的优势在于最后部分的纤维长度是可以达到的。与其他 lft 相比，GMT 在压缩成型之前不会被挤出，因此纤维损伤和磨损减少。为了分析加工过程中纤维性能的影响，使用了不同纤维含量和纤维长度的 GMT 材料。表一给出了所用材料的概述。...
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