Characterisation of discontinuous carbon fibre preforms for automotive applications
Characterisation of discontinuous carbon fibre preforms for automotive applications
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汽车应用不连续碳纤维预制件的表征
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发表时间：
2013
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通讯作者：
Giridharan Kirupanantham
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作者：
Giridharan Kirupanantham
原材料成本高、劳动力成本高和周期时间长限制了传统帘布层复合材料在汽车行业的使用。本论文旨在确定低成本不连续纤维复合材料（DFC）在结构应用中的潜力。 DFC 的性能取决于增强材料的均匀程度和纤维端部的不连续性，这会导致应力集中；从而限制了材料的机械性能。这项工作的重点是由机器人喷涂工艺制造的不连续碳纤维预成型件模制而成的层压板的材料特性。通过这项工作的最终成果，已经确定了适合汽车应用的设计方法。还考虑了航空航天的设计程序。
已经开发出一种分析模型来确定不连续碳纤维预成型复合材料的拉伸刚度和强度。该模型可用于汽车和航空航天设计方法来定义材料属性，但必须考虑许多其他因素。预成型件的面积质量已被确定为实现目标压实水平的控制因素。薄部件的均匀性差阻碍了获得高体积分数的能力，而高体积分数决定了机械性能。事实证明，与连续纤维复合材料相比，基体对 DFC 的性能影响更大。增韧树脂对于提高均质性较差的 DFC 的拉伸强度特别有效。 DFC 的损伤容限通过冲击测试后的开孔和压缩进行了评估。与连续纤维同类产品相比，观察到更高的性能保留。 DFC 更高的损伤容限可能会导致结构应用中的重量减轻。然而，当前基于传统层压板的安全系数可能过于保守，可能导致过度设计，从而限制了材料的潜力。
The high cost of raw materials, high labour costs and lengthy cycle times have limited the use of conventional ply-based composites in the automotive industry. This thesis seeks to identify the potential of using low cost discontinuous fibre composites (DFCs) for structural applications. Properties of DFCs are governed by the degree of homogeneity of the reinforcement and discontinuities at the fibre ends, which cause stress concentrations; thereby limiting the mechanical performance of the material. This work focuses on material characterisation of laminates moulded from discontinuous carbon fibre preforms manufactured by a robotic spray process. Through the culmination of this work, a suitable design methodology for automotive applications has been identified. Design procedures for aerospace have also been considered.
An analytical model has been developed to determine the tensile stiffness and strength of a discontinuous carbon fibre preform composite. The model can be used within automotive and aerospace design methodologies to define material properties, but a number of other factors must be considered. Areal mass of the preform has been identified as the governing factor in achieving target compaction levels. Poor homogeneity in thin parts prevents the ability to achieve high volume fractions, which determines mechanical performance. It has been demonstrated that the matrix has a greater influence on the properties of DFCs when compared to continuous fibre composites. Toughened resins were particularly effective in improving tensile strength of DFCs that exhibited poor homogeneity. Damage tolerance of DFCs has been evaluated through open-hole and compression after impact testing. Higher property retention was observed compared to continuous fibre equivalents. Greater damage tolerance of DFCs could lead to increased weight-saving in structural applications. However, current safety factors based on conventional laminates may be too conservative and could lead to over-engineering thus limiting the potential of the material.