Tools and Measures for High Precision Quantitative Computed Tomography (QCT) with Light Weight Composite Materials

With the growing use of CT systems in industrial non-destructive testing the spectrum of applications is widening. In order to optimize a CT system with respect to quantitative accuracy of the reconstructed values, the complete chain of data processing was analysed by the Fraunhofer EZRT during the research project "ZeLuR". Two new methods were developed that both allow for a highly accurate reconstruction of material properties. First, we implemented a helical data acquisition. In order to achieve the non-planar helical trajectory the object is rotated and shifted in vertical direction for each projection. The Feldkamp-type cone-beam reconstruction algorithm was adapted to the helical projection data. The advantages of the helical CT are shown with the reconstruction of a CD spindle. The second major focus of our work has lain on the development of dualenergy methods. With industrial applications there is a broad variety of materials, structures and object sizes, a dual energy CT system has to be prepared for. The aim of this work is to establish dual-energy CT as a tool for accurate quantitative measurement of an arbitrary object's composition. As test object a mixed material cube was used which is made of two materials. The result of the dual-energy evaluation is shown. Introduction Today, Computed Tomography (CT) is used for industrial testing predominantly as a reliable method to detect flaws, cracks, holes and others. The evaluation of 3-dimensional volume data is based on grey values that are usually reconstructed with an arbitrary scale. Inclusions or defects show up by a higher respectively lower grey value than the surrounding material, i.e. qualitatively as hyperrespectively hypodense regions. With the growing use of CT systems in industrial non-destructive testing the spectrum of applications is widening. On the other hand, new, light-weight composite materials become increasingly important especially in the production of aircrafts and automobiles. The inspection of this class of materials cannot be performed anymore by simply evaluating relative grey value contrasts. The quality standards for industrial inspection impose the request for a quantitative measurement of physical material properties such as mass density or the contribution of single composites for each reconstructed point in the 3D volume. For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=81 International Symposium on NDT in Aerospace December 3-5, 2008, Fürth, Germany