Discontinuous carbon fibre composites for automotive applications
Discontinuous carbon fibre composites for automotive applications
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用于汽车应用的不连续碳纤维复合材料
DOI：
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发表时间：
2006
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通讯作者：
L. Harper
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作者：
L. Harper
越来越严格的排放目标鼓励汽车制造商优先考虑减少车辆质量。碳纤维成本的下降正在提高轻质碳基车身板系统在广泛生产量范围内的可行性。在目前的工作中，已经开发出一种自动化工艺，用于制造中等批量生产水平（30-50，000 ppa）的随机纤维预制件。
本论文旨在了解碳纤维层压板的机械和物理性能的直接纤维预成型生产的关键微观结构参数的影响。研究的主要参数是纤维长度，丝束长丝数和层压厚度。一个统计过程模拟已被开发来预测预成形件的密度变化，并与实验拉伸性能的结果进行了比较。
实验研究表明，有一个显着的减少面密度变化，并因此增加了拉伸性能与较短的纤维（115毫米至6毫米）和较厚的层压板（1.5毫米至4毫米的恒定体积分数）。较短的长度提高了预成型件的覆盖率，并提供了更高的拉伸强度，而较厚的层压板减少了未加强的区域，导致应力集中的存在。当使用廉价的24 K束时，通过气动方式诱导丝束细化，以减少平均长丝数并最大限度地提高机械性能。通过最大限度地提高刚度和强度，可以分别增加20%和45%。
提出了一个分析刚度模型来预测丝束数对面内弹性常数的影响。长丝计数和平面外的纤维取向分布确定从光学显微镜，并纳入一个多层次的森田中为基础的模型。对于含有大纤维束的层合板，预测值与实验值相差在8%以内，而对于含有高度纤维束的层合板，预测值与实验值相差在10%以内。为了更准确地预测纤维束的强度，根据纤维束内的纤维数，提出了一个临界纤维束长度的表达式。实验结果证实，临界丝束长度与丝束支数成正比。
定向纤维预成型在机械性能、重量节省潜力和成本方面已与其他竞争工艺进行了比较。一个全尺寸的演示器组件已经使用各种碳复合材料解决方案制造出来，这些解决方案都可以提供40%到50%的重量节省，与钢具有相同的弯曲刚度，并大大提高了抗凹陷性。定向纤维预成型已经显示出对于中等体积应用的半结构和结构部件的巨大前景，特别是当引入定向纤维时。这项工作的结果可以直接用于工业应用，以提供一种具有成本效益的轻质钢替代品。
Increasingly stringent emissions targets are encouraging vehicle manufacturers to prioritise reduction of vehicle mass. The falling cost of carbon fibre is increasing the viability of lightweight carbon-based body panel systems across a broad range of production volumes. In the present work an automated process has been developed for the manufacture of random fibre preforms at medium volume production levels (30-50,000ppa).
This thesis seeks to understand the influence of key microstructural parameters on the mechanical and physical properties of carbon fibre laminates produced by directed fibre preforming. The principal parameters studied are fibre length, tow filament count and laminate thickness. A statistical process simulation has been developed to predict preform density variation and the results are compared with experimental tensile properties.
Experimental studies have shown that there is a notable reduction in areal density variation and consequently an increase in tensile properties with shorter fibres (115mm to 6mm) and thicker laminates (1.5mm to 4mm for a constant volume fraction). Shorter lengths improved preform coverage and gave higher tensile strength, whilst thicker laminates reduced the presence of unreinforced areas which cause stress concentrations. Tow filamentisation has been induced by pneumatic means to reduce the mean filament count and maximise the mechanical performance when using inexpensive, 24K bundles. By maximising the level of filamentisation both stiffness and strength can be increased by 20% and 45% respectively.
An analytical stiffness model is presented to predict the effect of tow filament count on the in-plane elastic constants. Filament count and out-of-plane fibre orientation distributions are determined from optical microscopy and are incorporated into a multi-level Mori-Tanaka based model. Predictions are within 8% of the experimental data for laminates containing large fibre bundles and 10% for laminates with highly filamentised bundles. An expression for critical bundle length has been developed for more accurate strength prediction, based on the number of filaments within the bundle. Experimental results confirm that the critical tow length is proportional to the tow filament count.
Directed fibre preforming has been benchmarked against other competing processes in respect of mechanical properties, weight saving potential and cost. A full-scale demonstrator component has been manufactured using a variety of carbon composite solutions, which can all provide 40 to 50% weight saving for an equivalent bending stiffness to steel and greatly improved dent resistance. Directed fibre preforming has shown great promise for both semi-structural and structural components for medium volume applications, particularly when aligned fibres are introduced. The results from this work can be directly scaled for industrial application to provide a cost effective, lightweight alternative to steel.