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Non-destructive evaluation of advanced materials by synchrotron radiation refraction topography
(2002)
High performance composites and other light weight materials are generally a comple problem to the performance of nondestructive testing methods. X-ray refraction provide unconventional X-ray scattering techniques to meet the actual demand for improve nondestructive characterization of these advanced materials. Scanning the samples across collimated narrow incident X-ray beam permits to image integral micro-structures (a present) with a resolution of 10 µm. Investigations of samples after strain-induced micro cracks and fibre debonding in impact damaged epoxy are shown.
The physics of X-ray refraction are analogous to the well known refraction of light b optical lenses and prisms, governed by Snell's law. The special feature is the deflection a very small angles of few minutes of arc, as the refractive index of X-rays in matter i nearly one. Due to the density differences at inner surfaces most of the incident X-rays ar deflected. As the scattered intensity of refraction is proportional to the specific surface of sample, a reference standard gives a quantitative measure for analytical determinations.
Figure 1 represents a two-dimensional damage distribution of an impact in a 0/90° CFR laminate of 3 mm, thickness. Unlike in ultrasonic testing, there is no shadowing effect o the successive layers. By use of X-ray refraction the exact concentration of debonde fibres is calculated for each position. Additionally the refraction allows the selection of th fibre orientation.
Micro damage structures of fiber reinforced polymers (FRP) can be characterized nondestructively by X-ray refraction topography, which images inner surfaces. The damage accumulation after fatigue treatment of short glass fiber reinforced polybutylene terephthalate (PBT-GF) is correlated to the applied load and the number of cycles. Micro cracks and fiber/matrix debonding during fatigue can be detected separately due to their different direction of X-ray small angle scattering. The residual strength over the crack surface decreases by a linear decay as 30 %, 60 % and 90 % of the materials lifetime is passed.
HYJECT
(2002)
Quantitative X-ray refraction topography is applied for improved nondestructive evaluation of advanced high performance ceramics. The method is based on X-ray small angle scattering by refraction of X-rays due to density differences of microstructures in heterogeneous materials. It determines the amount of inner surfaces and interfaces within the range of µm to nm dimensions. As the scattered refraction intensity is proportional to the inner surface density of a sample, a reference standard gives a quantitative measure for analytical requirements. X-ray refraction scanning topography visualizes integral interface properties at 10 µm spatial resolution by two-dimensional computer images. Characteristic microstructure parameters, i.e. density fluctuation, porosity and pore size distribution of several examples of SiO[2]-and SiC ceramics at different stages of sintering are presented.