Abstract
This paper evaluates the precision of polarisation imaging technology for the inspection of carbon fibre composite components. Specifically, it assesses the feasibility of the technology for fibre orientation measurements based on the premise that light is polarised by reflection from such anisotropically conductive surfaces. A recently commercialised Sony IMX250MZR sensor is used for data capture by using various lighting conditions. The paper shows that it is possible to obtain sub-degree accuracy for cured and dry woven and unidirectional materials in ideal conditions, which comprised dark field illumination. Indeed, in ideal conditions, the average relative angles can be measured to an accuracy of 0.1–0.2°. The results also demonstrate a precision of the order 1° for more general illumination, such as dome illumination and ambient lighting, for certain material type/lens combinations. However, it is also shown that the precision varies considerably depending on illumination, lens choice and material type, with some results having errors above 2°. Finally, a feasibility study into the inspection of three-dimensional components suggests that only limited application is possible for non-planar regions without further research. Nevertheless, the observed phenomena for such components are, at least, qualitatively understood based on physics theory.
Highlights
The use of composite structures in various industries has increased in recent decades due to their advantages over conventional materials
In the case of carbon fibre composites, the Fresnel theory breaks down. This is because the dominating cause of polarisation is no longer geometry of the surface and capture environment, as in most previous research, but rather the individual fibres affecting the directionality of the electric field of the reflected light
The results presented in this paper have been produced by using the following carbon fibre reinforced polymer (CFRP) sample types to represent a broad range of application areas in various industry sectors:
Summary
The use of composite structures in various industries has increased in recent decades due to their advantages over conventional materials. CFRP usage is becoming increasingly popular in other areas such as maritime, civil and automotive engineering [1] Due to this increased use of CFRP—in addition to its higher manufacturing costs—the need for inspection and repair technologies for such materials has increased . This is important since the strength and stiffness of composite parts are highly dependent on the placement and orientation of fibres during manufacture [2]: a 5° angular error in orientation, for example, can result in a 20% reduction in component strength [3]. Precise measurement of fibre orientation plays an important role during manufacturing quality assurance
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