This paper presents details of a novel photoelectric system for intelligent structural health monitoring in aircrafts.
Through light intensity-based experiments about loads and damages of an aircraft composite structure conducted in this
paper, the potential for structural health monitoring of the composite material is discussed. Firstly, the paper
demonstrates the design of a novel photoelectric system including an optical part and a circuit part. The former part
consists of a light resource group and fiber optical sensors. And the latter part of this system is composed of a monitoring
host and a computer, both of which work together under the instructions given by self-designed software. The schematic
hardware diagram and the flow chart of the main program of the software are specified in this paper. In order to assess
the monitoring effect, the loads experiments are carried out at different locations of a test object in which special optical
fibers are buried. Finally, the degrees of loads and damages are measured and the experimental results are discussed.
Results obtained offer feasibilities of employing the proposed photoelectric system as a monitoring device for load and
damage detection in intelligent composite structures.
With the increasing development of material technology and electronic
integration technology, optical fiber and its using in smart structure have become hot
in the field of material research. And liquid-core optical fiber is a special kind of
optical fiber, which is made using liquid material as core and polymer material as
optical layer and protective covering, and it has the characteristics of large core
diameter, high numerical aperture, large-scope and efficient spectrum transmission
and long life for using. So the liquid-core optical fiber is very suitable for spectrum
cure, ultraviolet solidification, fluorescence detection, criminal investigation and
evidence obtainment, etc, and especially as light transfer element in some new
structures for the measurement of some signals, such as concentration, voltage,
temperature, light intensity and so on. In this paper, the novel liquid-core optical fiber
is self-made, and then through the test of its light transmission performance in free
state, the relation between axial micro-bend and light-intensity loss are presented.
When the liquid-core optical fiber is micro-bent axially, along with the axial
displacement's increase, output power of light is reducing increasingly, and
approximately has linear relation to micro-displacement in a range. According to the
results liquid-core fiber-optic micro-bend sensor can be designed to measure
micro-displacement of the tested objects. Experimental data and analysis provide
experimental basis for further application of liquid-core optical fiber.
Composite material has been applied widely in aeronautics, astronautics and some other fields due to their high strength, light weight and antifatigue and etc. But in the application, composite material may be destroyed or damaged, which may have impact on its further applications. Therefore, study on the influence of behavior of composite material damage becomes a hot research. In this paper, the common composite material for aircraft is used as the test object, and a study is conducted to investigate the influence of vibration behavior of composite material damage. The authors adopt the method of light-carrier wave and time-average holography. Compared the interference fringes of composite materials before and after damage, the width of the interference fringes of hologram of the damaged composite material is narrower than that of the fringes before. It means that the off-plane displacement of each point on the test object is larger than before. Based on the elastic mechanics theory, the off-plane displacement is inverse to the bending stiffness, and the bending stiffness of the test object will decrease after it is damaged. In other words, the vibration property of the composite material changes after damages occur. The research results of the paper show that the results accord with the analysis of theory.
Based on current trends in research on techniques for repairing composite materials, this paper focuses on the compatibility between a light-cured repair material and composite materials. The repair material used in this study is intended to find applicability in techniques for repairing damaged composite materials. Test pieces of the composite material were excited by a sinusoidal acoustic source at a frequency of 1058 Hz. Time-average holographic interferograms were photographed in original, damaged, and repaired samples. By analyzing the three interferograms according to the principles of holographic interferometry, the utility of the light-cured repair material is shown.