長纖維增強聚合物的輕量化設計. 由于纖維基體分離的影響而帶來的技術挑戰
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- 畢設文獻翻譯全球汽車制造商的目標是減輕汽車的重量，因為由于消費者需求和政府規定，更多的電器、功能和安全特性被整合在一起。隨著電動火車、全電動汽車或混合動力汽車的增加，電池的重量顯著增加了汽車的總重量。未來汽車的目標是減輕重量，以實現更嚴格的碳排放法規[1-3] ，同時仍保持良好的性能。纖維增強聚合物(FRP)為大規模生產提供了較高的機械性能和較低的成本。通過與其他輕質材料的智能結合，FRP 使未來輕質設計成為可能。
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.
不連續 FRP 加工的虛擬過程模擬工具，最大限度地減少了零件設計和評估過程中不必要的加工步驟。商業上可用的模擬工具被用來模擬加工過程中的許多效果。在纖維增強聚合物領域，由此得到的纖維參數(取向、長度、含量)在復合材料中具有重要的價值，特別是在結構和安全相關部件中的應用。通過在過程模擬中使用預測的纖維參數，可以精確地模擬多種情況下的組件行為，如碰撞和疲勞。目前的模擬工具具有多種模型可用于預測纖維取向[4]和纖維長度退化[5]。隨著纖維長度的增加，整個組件中出現不均勻的纖維密度分布。目前的模擬工具并不能充分代表這種現象。
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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]中已經提到，但迄今為止尚未徹底檢查。Schmachtenberg 等[7]用 BMC 進行的纖維含量實驗表明，與加工參數相比，在流動路徑上纖維含量增加。Londoño 等人的實驗[8]顯示斷路器箱中纖維含量的顯著變化。Londoño 首次介紹了在肋骨幾何形狀上工作的復雜力以及纖維和基質之間復雜相互作用的原理。他描述了肋骨幾何形狀充模過程中的兩種控制力。根據 Londoño 的理論，纖維根據達西定律(Eq. 1)擠入肋骨，達西定律描述了流體在多孔介質中的流動與流體速度(v)、孔隙度(κ)、粘度(η)和氣壓梯度(dp/dx)的關系。Bakharev 和 Tucker [9]預測了玻璃纖維床的滲透率(Eq. 2)。
(1) (2)
(1)(2)
The hydrodynamic force on the fiber at the rib entrance can then be calculated as the pressure on
在肋骨入口處的纖維上的流體動力可以計算為
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.
有效纖維面積，如 Londoño 等(3)中所描述的，這里是壓力機的閉合速度，Lrib 是肋骨的寬度，l 是纖維束的長度。
(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.
根據 Londoño 等[8]的理論，抵消纖維擠入肋骨幾何形狀的力可用將纖維彎入肋骨所需的力(f)表示(Eq)。4) ，其中(Cf)為常數，(e)楊氏模量，(EI)轉動慣量，(δ)光纖的撓度，(Lr)自由撓度長度。
(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 引入了纖維矩陣分離常數 θ，描述了纖維偏轉力與流體力學力的比值(Eq)。5).當纖維彎曲力大于流體力學力，基體被擠出纖維床層時，當 θ < 1時，發生 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.
建議的連續介質模型描述了纖維和聚合物基體作為兩相流的相互作用(圖1)。在此基礎上，將纖維和聚合物基體分為兩個獨立的區域，分別表示為彈性纖維區域(灰色，速度矢量 v)和粘性聚合物基體區域(紅色，速度矢量 u)。這兩個域如纖維矩陣分離常數中所述相互作用。彈性纖維力與粘性流體力的比值 θ 描述了兩相流動的差異。反作用力的簡化描述如圖2所示。在纖維基體分離過程中，彈性纖維受力大于水動力，導致流動前沿纖維含量降低，沿流動路徑形成團聚。
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Figure 1: A continuum model of a two phase flow of matrix (red) and fiber phase (grey)
圖1: 基質(紅色)和纖維相(灰色)兩相流動的連續模型
Figure 2: Interaction of the elastic fiber and viscous matrix domain in a continuum model for Fiber Matrix Separation
圖2: 纖維基質分離連續模型中彈性纖維和粘性基質域的相互作用
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.
本文在長玻璃纖維增強熱塑性材料的壓縮成型實驗中，考察了纖維基體分離的影響。所選擇的模具幾何形狀具有一系列不同的肋骨與交替設計。分析了不同材料特性和肋條設計對纖維基體分離的影響。在這種情況下，纖維性能的測量使用傳統的過程，如熱解以及國家最先進的 CT 成像。然后分析收集的數據并將其與過程模擬結果進行比較。
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.
采用瑞士倫茨堡 Quadrant 公司提供的玻璃墊熱塑性薄板(GMT)進行了壓縮成型實驗。GMT 是通過在帶式壓力機中用熱塑性樹脂浸漬針狀玻璃墊而制造的。GMT 的優勢在于最后部分的纖維長度是可以達到的。與其他 lft 相比，GMT 在壓縮成型之前不會被擠出，因此纖維損傷和磨損減少。為了分析加工過程中纖維性能的影響，使用了不同纖維含量和纖維長度的 GMT 材料。表一給出了所用材料的概述。...
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