Optical Material Characterisation of Prepreg CFRP for Improved Composite Inspection

Abstract

Automated fibre layup techniques are often applied for the production of complex structural components. In order to ensure a sufficient component quality, a subsequent visual inspection is necessary, especially in the aerospace industry. The use of automated optical inspection systems can reduce the inspection effort by up to 50 %. Laser line scan sensors, which capture the topology of the surface, are particularly advantageous for this purpose. These sensors project a laser beam at an angle onto the surface and detect its position via a camera. The optical properties of the observed surface potentially have a great influence on the quality of the recorded data. This is especially relevant for dark or highly scattering materials such as Carbon Fiber Reinforced Plastics (CFRP). For this reason, in this study we investigate the optical reflection and transmission properties of the commonly used Hexel HexPly 8552 IM7 prepreg CFRP in detail. Therefore, we utilise a Gonioreflectometer to investigate such optical characteristics of the material with respect to different fibre orientations, illumination directions and detection angles. In this way, specific scattering information of the material in the hemispherical space are recorded. The major novelty of this research are the findings about the scattering behaviour of the fibre composite material which can be used as a more precise input for the methods of image data quality assessment from our previous research and thus is particularly valuable for developers and users of camera based inspection systems for CFRP components.

Sensor-guided machining of large-scale CFRP components based on resin transfer molded features

“…Thus, the observed reflections are a combined interaction of the different effects, e.g., multiple diffuse reflection, scattering, refraction, and partial absorption of the incoming rays, as well as the superposition of the rays reflected by the surfaces or intermediate layers. In the research the influence between inclination angle, polarization and fiber shape [53,55,66,67], the orientation to the fiber [56,68] as well as the structure of several fiber layers [44,53,55] is discussed. Depending on the application, it may be sufficient to estimate the behavior using empirical values [7,53,54].…”