X-ray computed tomography (XCT) is a promising technique that enables the possibility of achieving the virtual model of an object, in non-destructive way, by irradiating it with X-rays. The object is rotated between an X-ray source and a detector and radiographs are acquired at different angles, which are computed in order to reconstruct the volumetric data. The object under examination, unlike other techniques, does not come into contact with the instrumentation. This characteristic, along with the possibility to evaluate both the external and the internal geometries of an object, made XCT a widely used technique in the industrial field for non-destructive testing and material characterization and, lately, in the field of manufacturing metrology. Since XCT is increasingly used to perform dimensional analyses of industrial components characterised by complex shape and internal features, there is a need for internationally accepted standards and regulations in order to provide traceable measurements and robust procedures for the metrological performance verification of XCT system. Moreover, in order to meet the industry requirements, the process of accuracy enhancement of XCT based dimensional measurements is fundamental. The concept of measurement traceability is of the primary importance and its achievement is linked to the determination of the measurement uncertainty. However, the measurement chain of XCT is subject to a large number of influence factors, e.g. the geometry and the material of the object to be measured, the hardware components, the post-processing of the data, the surrounding environment and the operator, which must be identified and investigated. Among these quantities, the geometrical configuration of an XCT system, i.e. the relative position of the main hardware components, is of the most importance. This thesis aims at investigating two of these influence quantities in order to characterize their effects on the measurement results, enhancing the accuracy of XCT-based dimensional measurements. In particular, the geometry of a specific configuration of an industrial XCT system is studied with the scope of developing a method for the characterization of such geometry. An experimental campaign was performed with the aim of investigating the effect of the object material on dimensional measurements. At the scope, a set of calibrated objects were designed, manufactured and calibrated.

Study of the effects of the system geometric errors and the workpiece material on X-ray computed tomography dimensional measurements

DONADI, MARIA ILARIA
2021/2022

Abstract

X-ray computed tomography (XCT) is a promising technique that enables the possibility of achieving the virtual model of an object, in non-destructive way, by irradiating it with X-rays. The object is rotated between an X-ray source and a detector and radiographs are acquired at different angles, which are computed in order to reconstruct the volumetric data. The object under examination, unlike other techniques, does not come into contact with the instrumentation. This characteristic, along with the possibility to evaluate both the external and the internal geometries of an object, made XCT a widely used technique in the industrial field for non-destructive testing and material characterization and, lately, in the field of manufacturing metrology. Since XCT is increasingly used to perform dimensional analyses of industrial components characterised by complex shape and internal features, there is a need for internationally accepted standards and regulations in order to provide traceable measurements and robust procedures for the metrological performance verification of XCT system. Moreover, in order to meet the industry requirements, the process of accuracy enhancement of XCT based dimensional measurements is fundamental. The concept of measurement traceability is of the primary importance and its achievement is linked to the determination of the measurement uncertainty. However, the measurement chain of XCT is subject to a large number of influence factors, e.g. the geometry and the material of the object to be measured, the hardware components, the post-processing of the data, the surrounding environment and the operator, which must be identified and investigated. Among these quantities, the geometrical configuration of an XCT system, i.e. the relative position of the main hardware components, is of the most importance. This thesis aims at investigating two of these influence quantities in order to characterize their effects on the measurement results, enhancing the accuracy of XCT-based dimensional measurements. In particular, the geometry of a specific configuration of an industrial XCT system is studied with the scope of developing a method for the characterization of such geometry. An experimental campaign was performed with the aim of investigating the effect of the object material on dimensional measurements. At the scope, a set of calibrated objects were designed, manufactured and calibrated.
2021
Study of the effects of the system geometric errors and the workpiece material on X-ray computed tomography dimensional measurements
Computed Tomography
DimensionalMetrology
Measurement accuracy
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.12608/31706