Vibration analysis of composite airframe structural elements

制造更舒适、低成本、环保的飞机是下一代商用飞机的航空设计师的目标。纤维增强塑料（frp）在实现这些任务中发挥着关键作用，由于其良好的特定性能，可以大大减轻重量并提高有效载荷。当需要直接影响舒适性的噪声和振动阻尼时，这些材料的层流结构具有进一步的优势；橡胶层可以在制造过程中集成到层压板结构中，并且在使用过程中通过使其承受高剪切变形来利用其阻尼特性。由于层间强度较弱，分层可能是复合材料层板中最常见的损伤。由于制造工艺不完善或在使用过程中受到冲击，小裂纹可能会产生分层。已知分层的存在会导致强度和刚度退化，以及层压板振动特性的变化。一般来说，所有缺陷，特别是分层，都会降低固有频率，如果降低的频率接近工作频率，可能会引起共振。在动态环境中，我们必须能够预测频率以及模态振型的变化。我的研究计划的总体目标是提高我们对与机体结构相关的结构动力学和振动的理解，总的来说，特别是完整和损坏/有缺陷的层压复合材料/夹层结构元件。期望的结果有三个方面：提供知识，模型和强大的工具，这将更好地理解与损伤相关的问题，层压复合材料的振动行为以及损伤对结构行为的影响；开发高性价比的分析、半分析和数值模型以及专用模态分析工具，以达到所需的精度；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，这些领域的需求将在未来许多年继续增长。

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.