X-ray computed tomography (XCT) scanning is a powerful technique that can detect internal defects and produce quantitative information regarding the number, location, type, and size of these defects. Scans also differentiate between different materials making XCT a valuable non-destructive evaluation (NDE) technique that can be applied to numerous manufacturing operations including casting, welding, friction stir processing, and composite material lamination. However, when X-ray CT is employed as an NDE method the scanning parameters (image bit depth, scanning resolution, applied filters) and methodology (thresholding methodology, CT machine phantom calibration) are often underreported leading to a lack of consensus on the optimal scanning parameters to use when analyzing a particular metal or alloy. The Hounsfield Unit (HU) is widely adopted to analyze CT images and characterize materials by assigning an average HU value. Since this value will be dependent on the choice of X-ray CT parameters, it is beneficial to have a predictive methodology that will accurately determine the mean HU value of a material across a wide range of scanning parameters.In this study, 16-bit X-ray CT scans are employed to characterize the HU of AA6061, a common aluminum alloy. Identified as X-ray CT parameters that influence HU measurements, employed are four X-ray CT parameters namely: scan resolution, tube voltage, tube current, and sample thickness. Two levels of each parameter are used: scan resolution 0.0676-0.00423mm2, tube voltage 120-140kVp, tube current 50-200mAs, and sample thickness 1.5-6 mm. The two sample disks are scanned simultaneously at an image bit depth of 16-bit. The resulting Digital Imaging and Communications in Medicine (DICOM) images are then used to calculate the mean and standard deviation values for each sample. An analysis of variance (ANOVA) is then performed to generate a predictive model for the mean and standard deviation HU values. The resulting model is then used to determine the optimal scanning parameter combination for AA6061. The optimal scanning parameter combination is designated as the combination that results in the least standard deviation value of the mean HU value. The findings show that higher scanning resolution, larger tube voltage and tube current, and thicker samples result in lower standard deviation HU measurements values when scanning AA6061. It was also concluded that the most influential parameter affecting the mean HU values is found to be the scanning resolution, as for the standard deviation values, the sample thickness is determined to have the most prominent effect.Keywords: AA6061-T6, X-ray Computer Tomography, Hounsfield Unit, analysis of variance.

X-Ray Computed Tomography (XCT) Scanning Parameters Effects on the Hounsfield Unit (HU) Measurements for AA2011

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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