Abstract

Due to the significant increase in composite materials that can be used in aviation structural elements, there is a strong need for their operational control. It is estimated that a significant part of the average modern aircraft lifecycle costs is related to inspection and repair, thus it is important to perform efficient and cost-effective maintenance and monitoring techniques to reduce lifetime costs. This study is concerned with integral state monitoring of aircraft structures made from composite materials. It deals with techniques for damage monitoring and quality control, equipment observation, planned prototype testing and research into the vibration properties of different composite structures. Operation, maintenance and condition forecasting of components, such as aircraft composite blades, airplane spoilers, ailerons, aircraft airframe components, are the areas that should be properly investigated, in order to enhance the future of the industry.
The aim of this research is to investigate usable signs of vibration characteristics that can reflect the effects of the damage and integral changes of advanced composite structures. The main goals are a universal approach to integral condition monitoring for all kinds of composite materials and research into the vibration property alterations of a new generation of composite materials during their operation. The modern generation of large aircraft can be designed with all-composite fuselage, frames and wing structures. The main advantages of composite materials are their high strength, relatively low weight, corrosion resistance and flexibility in implementation. Control and diagnostics of this kind of composites require deep knowledge of composite structures, materials, their failure behaviour, and tooling. Aerospace structures are suffering from damage as a result of fatigue, overloading, partial or integral material destruction and degradation in consequence of environmental factors, and extemporaneous incidents such as seismic events or impacts.
There is also uncertainty connected to understanding the outcome of operational damage of aircraft composite structures. Non-destructive inspection and evaluation techniques are recommended in many cases, but still, represent significant downtime and labour costs and, in many cases, require highly skilled personnel to perform them. Linked to structures and onboard built-in structural health monitoring systems could be used for improving the reliability and safety of composites while reducing lifecycle costs and improving the design and manufacture processes. However, they also have their own disadvantages like the cost of implementation, cost of operation of the system itself and impact to the structure during production and maintenance.
This research is therefore mainly focused on vibration properties of advanced composite materials and simple control procedures that can be conducted by an engineering technician during light maintenance checks (including both routine and detailed inspections). The decision on the schedule for the checks to be performed can vary by aircraft type, the cycle count, or the number of hours flown since the last check. Another important subtask is the prediction of the object condition in operation. A significant part of the research is concerned with the collection of statistical information, and experiments with different objects made of composite materials, using the proposed methodology. An additional part is linked to the optimization of equipment for the future demands of the industry in operational control and diagnostics.
It is concluded that the technique of combining wavelet analysis is an effective and appropriate tool for vibration analysis to determine the modal parameters of free and forced oscillations, especially in the integral control of composite structural elements. The novel aspect of the research is the practical experimental work that has been executed on real advanced composite material objects (metal-polymer-metal composites as well), and its subsequent analysis.