FTIR SPECTROSCOPY AS A NONDESTRUCTIVE TESTING METHOD FOR CFRP SURFACES IN AEROSPACE

摘要

Lightweight design is a key enabler to improve products in aerospace. Carbon fibre reinforced plastic (CFRP) is a material to meet the requirements for lightweight design, for example due to its specific strength. The favoured joining technology for CFRP parts is adhesive bonding. The bond strength is strongly influenced by the surface properties. Therefore there is a need for nondestructive testing (NDT) methods to characterise the CFRP surface properties. In this work it was investigated, if Fourier Transform Infrared (FTIR) spectroscopy is a suitable NDT technology to characterize CFRP surfaces. A commercial handheld FTIR spectrometer was used. The information in the resulting FTIR spectra appears in different spectral regions, which leads to a complex interpretation of the spectra. For this reason, the collected spectra were used to build regression models with the Partial Least Squares (PLS) algorithm in order to predict material properties from the FTIR spectra. The focus of the presented investigations is the detection of thermal damage, the detection of contaminations, such as hydraulic fluids, and the measurement of moisture uptake within the laminate. Especially for thermal damage it could be shown that there is a good prediction quality on the interlaminar shear strength (ILSS). Furthermore the moisture uptake at homogenously saturated samples could be successfully quantified and an indicator for samples stored in a hydraulic fluid could be identified.