X-Ray Refraction Topography of Impact Damage of CFRP Laminates

Abstract

X-ray refraction topography is a new method for non-destructive testing in the field of X-ray methods. The refraction effect is based on the X-ray beam deflection at micro-surfaces of materials with different electron densities. At the interface of fibres in CFRP laminates X-ray waves are deflected similar to visible light in a lens. In this case, X-ray refraction essentially is caused by the differences in the index of refraction between the fibres and the surrounding matrix material. Depending on the interface concentration of bonded and debonded fibres in the composite the refraction factor C gives a measure for the specific inner surface density. It is determined by the relative difference between the measured refraction intensity IR and the absorption level IA. The knowledge of the amount of inner surfaces in a composite allows to characterise precisely the fibre/matrix-damage state and may help to predict the mechanical behaviour.

We present a series of two-dimensional X-ray refraction topographs of impacted 0°/90°-CFRP laminates. Unlike in ultrasonic testing there is no shadowing effect on the successive layers by delamination echoes. The refraction image inspections show that the fibre/matrix-damaged areas increase significantly with increasing impact energies. From the analytical investigation, we conclude a refraction value C which is proportional to the absorbed impact energy per layer. Furthermore, the X-ray refraction setup is sensitive to separate the orthogonal arranged fibre orientation. The presented X-ray refraction topographs show the selectively damaged composite states of both (0° and 90°) fibre directions and therefore give a more detailed information about the mechanical performance of CFRP laminates.