Micro- and nano-X-ray computed tomography

Micro- and nano-X-ray computed tomography

06. 12. 2018

X-ray computed tomography is an advanced imaging technology allowing non-destructive object visualisation and analysis. Microtomography allows the scanning of internal 3-D structures with high spatial resolution without any damage (mechanical or electrical) to the scanned object. A complete idea of the internal structural arrangement of the whole object volume can be obtained for a wide range of materials, making this method suitable for the detection of shapes of internal and external structures, inhomogeneities, cavities, and the material porosity.

The area of use for computed tomography is very wide and it can be applied in the mechanical, material, and electrotechnical engineering and building fields, as well as in a number of other non-industrial areas. Tomography analyses help in the areas of development, quality control, and resolving technological problems of individual parts, as well as in the development of complex technological units, reverse engineering, and inspection of inner/outer dimensions. Computed tomography also finds applications in the fields of plastics, ceramics, and light metal casting, component production, process control, and preparation.

A vital area of applied computed tomography is medicine, where this technology is used to study bones and implants, though it can also be found other fields like archaeology (research of museum artifacts), anthropology, conservation, forensic science, legal engineering, criminology, the food industry, etc.

Typical options of the tomographic data analysis are as follows:

1. Analysis of pores and inclusions

This analysis is used to detect and visualise pores and inclusions (defects) in the material of the scanned object. Usually it is possible to define volume, position, size, and surface area of the detected defect. Colour coding is usually used for easier orientation among individual defects.

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2. Measuring dimensions and geometrical tolerances

Definition of inner and outer dimensions, and the availability and accuracy of such knowledge are major requirements in all the fields where the dimensional parameters play central roles. Thanks to coordinate measuring, it is possible to determine the surface of an object based on the threshold values adopted to the local grey levels. To measure dimensions and geometrical tolerances, filtering tools are available, which fit geometric shapes like circles, planes, cylinders, cones, or spheres to the volume data. The advantage of dimension measurements based on tomography data compared to standard methods like Coordinate Measuring Machines (CMM), or mechanical or optical 3D scanners, is that this method provides the ability to measure dimensions or shapes of inaccessible places of the part, such as the height and recess diameter of a hole (see the picture below).

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3. Thickness measurement

Wall thickness analysis can investigate objects in areas, in which wall thickness is in a range between minimum and maximum allowable values. The results of analysed components are colour-coded according to the measured distances between the walls and are displayed as tomographic sections and 3D models.

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4. Analysis of fibre-reinforced composites

This module allows a range of important information on the composite material structure to be obtained using a non-destructive method. This may be take the form of local and global orientation and concentration of fibres, a deflection from the pre-defined reference orientation, a local orientation of fibres in a projections plane, or many other statistical parameters like the fibre distribution. The results may be displayed and recorded in many ways, including colour-coded fibre imaging in 2D or 3D, or using a histogram showing fibre distribution by orientation.

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Finally, it might be reiterated that the range of applications of computed tomography is very wide and this technology has only been gaining popularity in recent years.

Jiří Kouřil

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