Vibration analysis of composite airframe structural elements

制造更舒适、更低成本、更环保的飞机是下一代商用机队航空设计师的目标。纤维增强塑料(FRP)由于其良好的特性，在完成这些任务中发挥了关键作用，从而大大减轻了重量并改善了有效载荷。在这些材料的层状结构中设计出了另一个优点，当面对直接影响舒适性的噪音和振动抑制的需求时；橡胶层可以在制造过程中集成到层叠结构中，并通过使它们在使用中经受高剪切变形来开发它们的减振性能。脱层可能是复合材料层合板中最常见的损伤，因为其层间强度较弱。由于制造工艺不完善或在使用过程中受到冲击，可能会从细小的裂纹中产生分层。众所周知，分层的存在会导致强度和刚度的退化，以及层合板振动特性的变化。一般说来，所有缺陷，尤其是分层，都会降低固有频率，如果降低的频率接近工作频率，则可能会引起共振。在一个动态的环境中，我们必须能够预测频率和振型的变化。我的研究计划的总体目标是提高我们对与机身结构相关的结构动力学和振动的了解，特别是对完好和损坏/有缺陷的层合复合材料/夹层结构元件的了解。期望取得的成果有三个方面：提供知识、模型和强大的工具，以便更好地了解与损伤、层合复合材料的振动性能以及损伤对结构性能的影响相关的问题；开发成本效益高的改进的分析、半分析和数值模型以及专用的模态分析工具，以达到预期的精度；以及最后但并非最不重要的是，在结构动力学/振动和复合材料领域培训HQP，该领域的需求在未来多年将继续增长。

Making more comfortable, low cost, environmentally friendly aircraft is the goal of the aeronautical designers for the next generation commercial fleets. Fibre-Reinforced Plastics (FRPs) play a key role in the achievement of these tasks, allowing considerable weight savings and improvements in payload, owing to their favourable specific properties. A further advantage has been devised in the laminar structure of these materials, when the needs for noise and vibration damping, directly influencing comfort, have been faced; rubbery layers can be integrated into the laminate structure during the fabrication process, and their damping properties exploited by subjecting them to high shear deformations in service. Delamination is probably the most frequently occurring damage in composite laminates due to its weak interlaminar strength. Delaminations may develop from small cracks due to either imperfect fabrication processes or impact during service. The presence of the delaminations is known to cause strength and stiffness degradation, as well as changes of the vibration characteristics of the laminates. All defects, in general, and delaminations, in particular, reduce the natural frequency, which may cause resonance if the reduced frequency is close to the working frequency. It is imperative that we should be able to predict the changes in the frequency, as well as the mode shape, in a dynamic environment. The overall aim of my research program is to improve our understanding of the structural dynamics and vibration associated with airframe structures, in general, and the intact and damaged/ defective laminated composite/sandwich structural elements, in particular. The desired outcome is 3-fold: To provide knowledge, models and powerful tools, which will give a better understanding of the problems associated with the damages, the vibrational behaviour of laminated composites and the effects of damage on structural behaviour; To develop enhanced and cost efficient analytical, semi-analytical and numerical models and a dedicated modal analysis tool for desired precision; and last but not least, to train HQP in the field of structural dynamics/vibration and composites which will continue to grow in demand for many years to come.