Vibration Modelling and Analysis of Intact and Defective Composite Airframe Structural Elements

目前，航空运输在全球范围内提供了5660万个就业岗位，经济活动相当于全球gdp的3.5%，每年运送26亿人次，预计未来20年空中交通量将增长2.6倍2。相反，人们越来越担心航空对环境的影响越来越大，这使得社会对更环保的飞机的需求比以往任何时候都大。此外，环境绩效正在成为市场竞争力中越来越重要的因素。***复合材料，包括纤维增强塑料（frp）和纤维金属层压板（FML），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。此外，通过将多层阻尼材料集成到层压板结构中，可以实现直接影响乘客舒适度的噪声和振动衰减。玻璃纤维复合材料由于其高刚度和相对较低的成本也是生产风力涡轮机叶片的首选材料，碳纤维被用作高级复合材料的增强材料。分层和裂纹可能是复合材料层合板中最常见的缺陷。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，都会降低结构刚度，从而降低系统的固有频率，如果降低的频率接近工作频率，则可能引起共振。在动态环境中，预测频率和模态振型的变化是非常必要的。***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/振动的理解，一般来说，特别是完整和有缺陷的层压复合材料结构元件。期望的结果有四个方面：为了更好地了解与损伤相关的问题，层合复合材料的振动行为以及损伤对结构行为的影响；开发新的增强和成本效益（半）分析和高度收敛的数值模型和专用模态分析工具，以达到所需的精度和准确性；制定一个方案，能够预测缺陷的临界数量/大小/位置，这对容错/故障安全设计至关重要；最后，在结构动力学/振动和复合材料领域培训HQP，在未来的许多年里，需求将继续增长。******1ATAG“航空：超越国界的利益（2012）”，基于2010年的估计。***2JADC《全球商业航空运输市场预测20122031》（2012）

Air transportation currently supports 56.6 million jobs worldwide and economic activity equivalent to 3.5% of the global GDP1, carries 2.6B passengers a year, with the volume of air traffic expected to grow 2.6-fold in the next 20 years2. Conversely, there are growing concerns about the increasing environmental impacts of aviation, making the social need for more environmentally friendly aircraft greater than ever. Also, environmental performance is becoming an increasingly important factor in market competitiveness. ***Composites, including Fiber-Reinforced Plastics (FRPs) and Fiber-Metal laminates (FML), play a key role in the achievement of these tasks, allowing considerable weight savings and improvements in payload, owing to their favorable specific properties. Also, noise and vibration attenuation, directly influencing passenger comfort, can be achieved by integrating layers of dampening materials into the laminate structure. Glass fiber composites are also material of choice for the production of wind turbine blade due to their high stiffness and relatively low cost, and carbon fiber is used as reinforcement for advanced composites. *** Delamination and crack are probably the most frequently occurring defects in composite laminates. Delamination may develop from small cracks due to either imperfect fabrication processes or impact during service. The presence of the delamination is known to cause strength and stiffness degradation and changes in the vibration characteristics of the laminates. All defects, in general, and delamination, in particular, reduce the structural stiffness and consequently natural frequency of the system, which may cause resonance if the reduced frequency is close to the working frequency. It is imperative to be able to predict the changes in the frequencies and mode shapes in a dynamic environment.*** The overall aim of my research program is to improve our understanding of the structural dynamics/vibration associated with airframe structures, in general, and the intact and defective laminated composite structural elements, in particular. The desired outcome is 4-fold: To gain a better insight into the problems associated with the damages, the vibrational behavior of laminated composites and the effects of damage on structural behavior; To develop novel enhanced and cost efficient (semi-)analytical and highly convergent numerical models and dedicated modal analysis tools for desired precision and accuracy of results; To develop a scheme capable of predicting the critical number/size/location of defects, critical to fault-tolerant/fail-safe designs; and finally, to train HQP in the field of structural dynamics/vibration and composites, continuing to grow in demand for many years to come.******1ATAG “Aviation: benefits beyond borders (2012)”, estimation based on 2010.***2JADC “Worldwide Market Forecast For Commercial Air Transport 20122031” (2012)