X-ray refraction topography and computed tomography for NDE of lightweight materials (Keynote Paper)

Abstract

X-Ray Refraction Topography techniques are based on Ultra Small Angle Scattering by micro structural elements causing phase related effects like refraction and total reflection at a few minutes of arc as the refractive index of X-rays is nearly unity (1⋅10 -5 ). The extraordinary contrast of inner surfaces is far beyond absorption effects. Scanning of specimens results in 2D-imaging of closed and open pore surfaces and crack surface density of ceramics and foams. Crack orientation and fiber/matrix debonding in plastics, polymers and ceramic composites after cyclic loading and hydro thermal aging can be visualized. In most cases the investigated inner surface and interface structures correlate to mechanical properties. For the exploration of Metal Matrix Composites (MMC) and other micro structured materials the refraction technique has been improved to a 3D Synchrotron Refraction Computed Tomography (SR-CT) test station. The specimen is situated in an X-ray beam between two single crystals. Therefore all sample scattering is strongly suppressed and interpreted as additional attenuation. Asymmetric cut second crystals magnify the image up to 50 times revealing nanometer resolution. The refraction contrast is several times higher than "true absorption" and results in images of cracks, pores and fiber debonding separations below the spatial resolution of the detector. The technique is an alternative to other attempts on raising the spatial resolution of CT machines. The given results yield a much better understanding of fatigue failure mechanisms under cyclic loading conditions.

Detection system for microimaging with neutrons

“…The macroscope design has successfully been applied for synchrotron-based microimaging by the Federal Institute of Materials Research and Testing (Bundesanstalt für Materialforschung und -prüfung, BAM) [73], and then followed by other groups [74,75], to achieve visible light magnifications between 1× and 5× and Numerical Aperture (NA) around 0.4. Based on the combination of a visible light microscope with a folded optical beam path and a transparent thin film single crystal scintillator, synchrotron detectors of this type approach a resolution limit close to the diffraction limit of visible light [76].…”