X-ray Computed Tomography Method Research Articles

Prior function designs for X-ray reconstructions from limited angular views

The objectivity of three-dimensional imaging has placed X-ray Computed Tomography (CT) into an indispensable diagnostic method in clinical and industrial applications. Despite the advances in the X-ray CT imaging, high- resolution three-dimensional reconstruction of small details in objects with large in-plane dimensions has been a fundamental challenge for the conventional X-ray CT method. An alternative scanning geometry, where X-ray source and a detector move synchronously irradiating a specimen at an inclined angle, has been proposed to address this challenge. This work presents new designs of prior (or penalty) functions developed for reconstructing the radiography data obtained under the limited angular conditions. The new prior targets reduction of shape distortion artifacts, common for laminographic reconstructions, as well as preservation of small features, such as voids, edge details, and high-density inclusions. The novel prior function designs are demonstrated on the computational phantom of a specimen scanned under tilted planar CT geometry simulating large planar dimensions of a specimen. To accommodate physical CT scanning of such specimens, a novel microfocus X-ray CT scanning device that rotates X-ray source and moves the detector synchronously while staying on the same side of the test specimen (Inclined CT), is introduced. This device allows scanning of critical areas of up to 3-meter-wide and potentially unlimited length specimens with high resolution required for identification of manufacturing and structural defects typical for modern composite structural elements used in the aerospace industry.

Effect of barbotage refining time and recycled scrap content on the microstructure of EN AC 44200 alloy

The article presents the results of research on the effect of the barbotage refining time and recycled scrap content on selected properties, the microstructure and the degree of gasification of the EN AC 44200 alloy (EN AC-AlSi12). The input material consisted of various proportions of pure ingots and scrap; the scrap contents were 80%, 70% and 60%, respectively. Each batch of material was subjected to different refining times, which were 0, 7, 9 and 15 min, respectively. Microstructure studies were conducted with the techniques of light and scanning electron microscopy. Additionally, the distribution of pores in the volume of the material and their proportion were determined by means of the X-ray computed tomography method. In addition, the hardness and degree of gasification depending on the refining time were performed. It was proved that the refining process fosters homogenization of the microstructure and reduces porosity. Moreover, extending the refining time has a positive effect on reducing the porosity of thin-walled castings and reducing the level of outgassing of the alloy.

Decoupling polymer molecular chains and carbon fibres orientation by their dielectric anisotropy

Carbon fibre reinforced polymers (CFRPs) are widely used in various industry fields, owing to their superior mechanical properties. The orientation of polymer molecular chains and carbon fibres plays a crucial role in determining the mechanical properties of CFRPs. The complex interactions between them often lead to ambiguous dominant rules of mechanical properties. However, existing methods cannot decouple the orientation of polymer molecular chains and carbon fibres, resulting in the above-mentioned problems remaining a challenge. In this study, the orientation dynamics of polymer molecular chains and carbon fibres was decoupled by the dielectric anisotropy method for the first time. The accuracy of the decoupled orientation of polymer molecular chains and carbon fibres was verified by the polarized Raman spectroscopy and X-ray computed tomography methods. Noteworthily, linear low-density polyethene (LLDPE) orientation dominates the elastic modulus of LLDPE/carbon fibre was proved. Our method opens a new window for the design of high-performance CFRPs.

X-ray Computed Tomography (CT) to Scan the Structure and Characterize the Mud Cake Incorporated with Various Magnetic NPs Concentration: An Application to Evaluate the Wellbore Stability and Formation Damage

The X-ray computed tomography method has provided unrivalled data about the characterization and evolution of the internal/external structure of materials by analyzing CTN and non-destructive imaging approach. Applying this method on the appropriate drilling-fluid ingredients plays a significant role in generating proper mud cake quality to stabilize wellbore, and avoid formation damage and filtration loss by preventing drilling fluid invasion into the formation. In this study, smart-water drilling mud containing different concentrations of magnetite nanoparticles (MNPs) was used to assess the filtration loss properties and formation impairment. Conventional static filter press, non-destructive X-ray computed tomography (CT) scan images and high-resolution quantitative measurement of CT number method were used to estimate the filtrate volume and characterize the filter cake layers, hence evaluating the reservoir damage through hundreds of merged images. The CT scan data were combined with the HIPAX and Radiant viewer digital image processing. The variation in CT number of mud cake samples under different concentrations of MNPs and without MNPs concentration were analyzed, and hundreds of 3D images as a cross-sectional profile were used. This paper highlights the importance of MNPs property in terms of minimizing filtration volume and improving mud cake quality and thickness, and hence improving the wellbore stability. From the results, a notable reduction of filtrate drilling mud volume and mud cake thickness to 40.9% and 46.6%, respectively, were recorded for drilling fluids incorporated with 0.92 wt.% of MNPs. However, this study asserts that optimal MNPs should be implemented to guarantee the best filtration property. As confirmed from the results, increasing the MNPs concentration beyond the optimal value (up to 2 wt.%) increased the filtrate volume and mud cake thickness by 3.23 and 33.3%, respectively. CT scan profile images show two layers of mud cake produced from water-based drilling fluids possessing 0.92 wt.% MNPs. The latter concentration was found to be the optimal additive of MNPs as it caused a decrease in filtration volume, mud cake thickness, and pore spaces within the structure of the mud cake. Using the optimum MNPs, the CT number (CTN) shows a high CTN and density material, and uniform compacted thin mud cake structure (0.75 mm). The produced thin mud cake layer reveals the precipitation or exchange of elemental/mineral composition during fluid-solid interaction. These results confirm that MNPs could help in avoiding or reducing the formation damage, driving away drilling fluid from the formation, and improving borehole stability.

Algorithm of Estimation of the Degree of Porosity Homogeneity of Foamed Concretes by Local Volumes by X-ray Computed Tomography Method.

X-ray CT is widely used to study the structure of foam concrete, the quality of which depends on the uniformity in porosity in local volumes (LV) of the samples. The purpose of this work is to substantiate the need to assess the degree of homogeneity of samples in terms of porosity according to LV. To achieve the goal, an appropriate algorithm has been developed and programmed in MathCad. To illustrate the capabilities of the algorithm, foam concrete modified with fly ash and thermally modified peat (TMP) was tested by CT. The information obtained by CT was processed by the proposed algorithm with variations in LV dimensions in order to estimate the distributions of mean values and standard deviations of porosity. Based on the data obtained, a conclusion was made about the high quality of foam concrete with TMP. The proposed algorithm can be used at the stage of improving the technologies for the production of high-quality foam concretes and other porous materials.

Comparative Study of 2D Petrographic and 3D X-ray Tomography Investigations of Air Voids in Asphalt.

Knowledge of the exact composition of building materials (aggregate, binder, air voids, etc.) is essential for the further development of more resistant and sustainable building materials. In numerous scientific studies, the material behavior of asphalt is tested using mechanical methods. Here, the overall material behavior is determined (bitumen, air voids, aggregate). With the advent of imaging techniques, it is becoming possible to determine the individual constituents separately and perform a more detailed analysis of their location, shape and composition. Three-dimensional and two-dimensional methods are available for this purpose. For this study, two different types of asphalt (porous asphalt and asphalt concrete) were analyzed using 3D X-ray computed tomography and asphalt petrology as 2D methods; the results of both investigations are compared. The objective of this study is to determine whether the 2D method provides suitable results for the microstructural analysis of asphalt samples and how the results differ from those studied by the 3D method. The comparison shows that both methods can be used to analyze voids in asphalt samples. The 2D method provides valuable insight into the distribution of voids in a sample. In addition to the distribution of voids within a 2D section, the 2D method can also be used to make some structural statements about the location and structure of the voids in the 2D plane. The X-ray computed tomography method allows more complex analyses of the pore structure because of the third direction (3D). In addition, the 3D method provides more data, so that the pore structure can be described even more precisely, and the pore size (length, width, height) can be mapped and analyzed with a high degree of accuracy.

Simulation of a TRISO MiniFuel irradiation experiment with data-informed uncertainty quantification

An irradiation experiment using tristructural isotropic (TRISO) fuel particles and the miniature fuel (MiniFuel) irradiation vehicle was performed in Oak Ridge National Laboratory’s High Flux Isotope Reactor (HFIR) to support development of the Kairos Power fluoride salt–cooled, high-temperature reactor (KP-FHR). This paper describes modeling predictions of temperatures and fuel burnup for the as-built experiment. An uncertainty quantification (UQ) analysis was performed to determine the effect of TRISO particle volume and position on the temperature predictions at various fuel heat generation rates (HGRs). This UQ study utilized fuel kernel position and volume measurements previously collected using X-ray computed tomography (XCT) techniques and Monte Carlo sampling methods to generate fuel compact cases that were then analyzed using a finite element thermal model. The UQ analysis indicated that uncertainty in calculated temperatures caused by varying TRISO particle arrangement is relatively small, even at high fuel HGR. Final predictions of particle temperatures throughout the irradiation are shown to be relevant to KP-FHR normal and off-normal operating conditions and to previous TRISO irradiation experiments. The combination of XCT with UQ analyses will inform post-irradiation examination (PIE) of the irradiated fuel compacts, and these analyses can be used to develop fuel performance models for coated particle fuel forms. Both PIE of separate-effects irradiation data and enhanced fuel performance modeling support accelerated qualification of TRISO fuels for a broad range of advanced reactor applications. The novel approach demonstrated here of measuring TRISO particle configurations with XCT methods and generating representative fuel compacts for finite element modeling and UQ analysis could be leveraged by the broader particle fuel community in the development of other TRISO fuel experiments in which these variables may have a significant impact on key outcomes.

Weathering of Viamão granodiorite, south Brazil: Part 2 – Initial porosity of un-weathered rock controls porosity development in the critical zone

The development of porosity during rock weathering is a key process controlling nutrients release, water holding capacity available for plants and water flow. Here we used X-ray Computed Tomography (XRCT) and 14C PolyMethylMethAcrylate (PMMA) autoradiography to show how cracks are created and enlarged during initial weathering stages (saprock and saprolite) of granodiorite in southern Brazil (Viamão - RS). The physical evolution is characterized by imaging the pore network, using 14C-PMMA and XRCT methods. Combined with bulk porosity measurements, they highlight the increase in porosity with the degree of weathering (un-weathered rock Φ = 1.66 %, saprolite Φ = 11.7 %). This increase is related to the joint increase of the density of the cracks (un-weathered rock D = 0.28 mm−1, saprolite D = 0.94 mm−1) and of the average opening of the microcracks (un-weathered rock w = 2.4 µm, saprolite w = 3.9 µm) and macrocracks (un-weathered rock w = 176 µm, saprolite w = 400 µm). However, these average crack openings do not account for the variability of the openings that govern the flows, characterized here by specific distribution ranging from the submicrometre to the centimetre scale.The results highlight that the pore network of the un-weathered rock plays a key role in the initial stages or incipient weathering. The density and aperture and cracks increase following the subcritical cracking concept and new pores are formed by chemo-mechanical processes. The presence/absence of initial fractures in the regolith is certainly a key parameter controlling the weathering of different rock types (mafic vs felsic).

Dynamic observation of a damping material using micro X-ray computed tomography coupled with a phase-locked loop

As rubber materials are used for damping, clarifying the relationship between the loss factor and microstructure would help develop high-performance damping materials. Although nondestructive observations using X-ray computed tomography (CT) under repetitive deformation have been reported, no observations have been reported at the submicron order that capture low-strain deformation, such as vibration exposure. The internal deformation behavior of materials with different loss factors has not yet been evaluated. This study proposes a dynamic X-ray CT method for specimens under tensile amplitudes, directly evaluating the internal deformation behavior of materials under dynamic conditions. The proposed 4D-CT has an excitation of 1 Hz and a spatial resolution of 0.5 μm. The local strain was obtained from X-ray CT at each phase, and the deformation behavior was evaluated. The results revealed that the peak of the local strain amplitude distribution curve decreased and the distribution widened as fine particles were mixed.

Grating-Based X-Ray Computed Tomography for Improved Contrast on a Heterogeneous Geomaterial

Phase-contrast X-ray imaging has shown its potential to capture at micrometric scale and in three dimensions (3D), the structure and deformation of poorly-absorbing soft materials such as polymers and biological structures. When composed of constituents that attenuate X-rays differently, heterogeneous hard materials are often well resolved in 3D using absorption-based X-ray computed tomography (CT) techniques. As a result, phase-contrast techniques have been less frequently used to image such materials. However, many geomaterials contain similarly X-ray attenuating constituents, thereby complicating the use of absorption-based X-ray CT methods. Here we present the innovative use of grating-based synchrotron radiation computed tomography, a phase-sensitive technique, in order to better identify the distribution of constituents within geomaterials. We show that this approach enhances the contrast between similarly X-ray absorbing constituents, and can be used to identify spatially small structures such as pores or mineral grains that are typically poorly resolved with conventional absorption-based X-ray CT.

The effect of cooling rate and degassing on microstructure and mechanical properties of cast AZ80 magnesium alloy

The effect of casting cooling rate and degassing on the mechanical properties of cast AZ80 alloy is investigated. A water-cooled copper mould with a wedge geometry is chosen for the casting, which provides different cooling rates at different sections. The casting is performed with and without the addition of hexachloroethane degassing agent. Macrohardness, hot compression, quasi-static tensile, and stress-controlled cyclic tests are performed to characterize the mechanical properties of the cast samples. The microstructure of the material is studied using optical microscopy and X-ray computed tomography methods. The connection between the microstructure and mechanical test results shows that the morphology of primary α-Mg and porosity defects affect the mechanical properties of cast AZ80. The casting cooling rate controls both of these microstructural features. Higher cooling rates result in a finer dendritic morphology of α-Mg that improves mechanical properties and creates a finer and more discrete morphology of β intermetallic particles. The fine dendritic morphology results in smaller interdendritic regions, which in turn prevents pore coalescence and negates the detrimental effect of porosity on the quasi-static tensile and cyclic properties. In lower cooling rates, where the coarse grain structure of the cast material cannot prevent pore coalescence, degassing benefits the mechanical properties, especially fatigue resistance, by reducing the volume fraction of porosity defects. Moreover, the hot deformation behavior of cast samples shows that the addition of the degassing agent and casting with a higher cooling rate improves the range of deformation conditions where cracking will not occur.

Defect Analysis of 316 L Stainless Steel Prepared by LPBF Additive Manufacturing Processes

The 316 L stainless-steel samples were prepared by laser powder bed fusion (LPBF). The effects of processing parameters on the density and defects of 316 L stainless steel were studied through an orthogonal experiment. The density of the samples was measured by the Archimedes method, optical microscopy (OM) and X-ray Computed Tomography (XCT). The microstructures and defects under different LPBF parameters were studied by OM and SEM. The results show that the energy density has a significant effect on the defect and density of the structure. When the energy density is lower than 35.19 J/mm3, the density increases significantly with the increase of energy density. However, when the energy density is larger than this value, the density remains relatively stable. The process parameter with the greatest influence on energy density is the hatch distance D, followed by laser power P, scanning speed V and rotation angle θ. In this paper, the optimum parameters consist of P = 260 W, V = 1700 mm, D = 0.05 mm and θ = 67°, in which the density is as high as 98.5%. In addition, the possibility and accuracy of the XCT method in detecting the discontinuity and porosity of 316 L stainless steel were discussed. The results show that XCT can provide the whole size and variation trend of pores in the different producing direction of LPBF.

X-ray Computed Tomography Method for Macroscopic Structural Property Evaluation of Active Twist Composite Blades

This paper describes an evaluation of the structural properties of the next-generation active twist blade using X-ray computed tomography (CT) combined with digital image processing. This non-destructive testing technique avoids the costly demolition of the blade structure. The CT scan covers the whole blade region, including the root, transition, and tip regions, as well as the airfoil blade regions, in which there are spanwise variations in the interior structural layout due to the existence of heavy instrumentation. The three-dimensional digital image data are processed at selected radial stations, and finite element beam cross-section analyses are conducted to evaluate the structural properties of the blade at the macroscopic level. The fidelity of the digital blade model is first assessed by correlating the estimated blade mass with the measured data. A separate mechanical measurement is then carried out to determine the representative elastic properties of the blade and to verify the predicted results. The agreement is found to be good to excellent for the mass, elastic axis, flap bending, and torsional rigidity. The discrepancies are less than 2.0% for the mass and elastic axis locations, and about 8.1% for the blade stiffness properties, as compared with the measured data. Finally, a sensitivity analysis is conducted to clarify the impact of modeling the sensor and actuator cables, nose weight, and manufacturing imperfections on the structural properties of the blade.

Quantitative X-ray computed tomography: Prospects for detailed in-situ imaging in bench-scale fire measurements

This paper examines how X-ray Computed Tomography (XCT) can provide detailed and quantitative in-situ measurements in bench-scale fire experiments. The method is illustrated by employing a tabletop X-ray system to image the combustion of different biomass samples heated by convection and radiation. The XCT measurements are utilized to evaluate the gas temperature and quantify the burning rates. In particular, quantitative measurements of the pyrolysis and char oxidation rates are obtained for different types of biomass. Simultaneous 3D gas temperature measurements are enabled by doping the flow with Kr, an inert X-ray contrast gas. To assess the capabilities of XCT as a quantitative and non-intrusive measurement technique, the accuracy of the method is evaluated through repeatability studies, whereas the invasive impact of the XCT method on the combustion is characterized experimentally and theoretically. Finally, the adsorption of Kr on the char during cooling is evidenced, and its impact on the measurements is discussed. This analysis highlights that the XCT solid measurements are entirely non-intrusive and are repeatable within 5% uncertainties, while using Kr for gas temperature measurements results in only a 15% lower heat transfer by natural convection.

X-ray Computed Tomography Method for Measuring Matric Suction of Micro-Sheet Materials Mixed Cs2SO4

In this paper, the X-ray computed tomography method was applied to measure the matric suctions of the glass-sheet samples. With the contributions of Cs2SO4 solution, the distributions of water among glass sheets were distinctly observed. The shape of the liquid bridges between the glass sheets are not simple circular ring, but rings with the triangular or quadrangular projective planes. Cs2SO4 resulted in the coefficient surface tension of the solution decreasing, which is the main reason that the tested values of matric suction were slightly higher than calculated. Overall, the differences between tested and calculated values are less than 3%, which testified that X-ray computed tomography method for measuring matric suction is feasible. The significance of this work is X-ray computed tomography method could be applied in unsaturated clay soil constituted by sheet particles.

Morphological characteristics of crack branching in asphalt mixtures under compression

Crack branching is a multi-crack propagation problem. Singular crack tip elements are frequently encountered, and defining the multi-crack tips’ enrichment functions is difficult. To overcome these drawbacks, this study used an already developed ordinary state-based peridynamics method to simulate crack branching in AC-13, AC-20, and PAC-13 asphalt mixtures. These asphalt mixtures’ digital images were acquired by an X-ray computed tomography method. Next, the Prony series coefficients of the fine asphalt mixtures were obtained by the dynamic modulus test. After that, the fracture energy of the fine asphalt mixtures was measured by the semi-circular bending test. Finally, the measured asphalt mixture properties were input into the ordinary state-based peridynamics method in order to simulate crack branching in the AC-13, AC-20, and PAC-13 asphalt mixtures. The simulation results indicate that the diagonal crack first emanates in asphalt mixtures. Then, the diagonal crack continues to branch into a wing crack, splitting crack, and branched crack. These four types of cracks can generate eight crack branching categories in asphalt mixtures. The crack branching trajectory was quantified by the fractal dimension, whose value ranged from 1.14 to 1.64. The physical significance of the fractal dimension explains the changes of crack branching paths in the asphalt mixtures.

Effects of Rock Fragments on the Soil Physicochemical Properties and Vegetation on the Northeastern Tibetan Plateau

Stony soils are very widely distributed and contain abundant rock fragments (>2 mm), which impose major effects on soil properties and plant growth. However, the role of rock fragments is still often neglected, which can lead to an inadequate understanding of the interaction between plants and soil. Undisturbed soil columns were collected from three alpine grasslands on the Qilian Mountain, and the X-ray computed tomography method was applied to investigate the characteristics of rock fragments. The results showed there was significant difference in number density, volumetric content and surface area density of rock fragment among the three grasslands, and followed the order of alpine meadow > alpine steppe > alpine desert steppe. In addition, the soil organic carbon, total nitrogen, total phosphorus, available phosphorus, N-NH4+, and N-NO3− contents in fine earth all increased with increasing number density, volumetric content and surface area density but to different degrees. Furthermore, positive correlations were observed between the rock shape factor and belowground biomass (R2 = 0.531, p < 0.05), between the rock volumetric content and aboveground biomass (R2 = 0.527, p < 0.05), and between number density and Simpson’s index (R2 = 0.875, p < 0.05). Our findings suggest that within a certain range, the increase in rock fragment content is conducive to soil nutrient accumulation and soil water storage and circulation and changes plant features, which contributes to the growth of plants. In addition, rock fragments should be given more consideration when investigating the relationships between soil and vegetation and their response to climate change in future studies.

Microstructure reconstruction of the gas diffusion layer and analyses of the anisotropic transport properties

The gas diffusion layer (GDL) is a key component in a proton exchange membrane fuel cell and a comprehensive understanding of its transport properties is imperative for improving the performance and durability of a fuel cell. In this study, two microscopic reconstruction methods, stochastic numerical and X-ray computed tomography (XCT) reconstruction, are employed to generate 3D microstructure of two different types of GDL. The stochastic numerical reconstruction method simulates all available phases, including the pores, carbon fibers, binders, and PTFE, to generate the 3D microstructure of the GDL in comparison with experimentally obtained GDL using the XCT method. The porosity and pore size distribution of the reconstructed GDL are compared and analyzed. Pore scale model is employed to obtain the effective and anisotropic transport properties including gas diffusivity, electrical and thermal conductivity as a function of porosity caused by different compression strain. Furthermore, Lattice-Boltzmann method is used to determine the anisotropic liquid water permeability and saturation as a function of capillary pressure. The results show significant anisotropic transport properties of Toray GDL due to its disc-shape binder existed at the intersection of the fibers. On the other hand, Freudenberg GDL shows mostly isotropic transport properties due to its uniformly distributed carbon fiber without binder. The combined results not only provide a reliable framework for investigating GDL microstructure, but also provide useful property correlations for fuel cell simulations and operations.

X-ray Computed Tomography for the ex-situ mechanical testing and simulation of additively manufactured IN718 samples

The aim of this work is to present the quantitative evaluation of the Additive Manufacturing (AM) laser powder bed fusion (L-PBF) process steps and validation of the FE (Finite Elements) simulation results using the X-ray Computed Tomography (XCT) based approach. The characterization of the production process was made using standard methods, including: laser light diffraction, optical and scanning electron microscopy, hardness examinations, and the investigation of mechanical properties. The XCT method was used to conduct the quality of powder feedstock, the influence of the L-PBF build strategy on the samples’ porosity, and also to evaluate a quantitative analysis of damage behavior before and after ex-situ mechanical testing. The porosity recorded for the powder feedstock was 0.2% and for test samples did not exceed 0.02%. The majority of the observed pores are aligned in patterns connected with the scanning strategy and were arranged in lines appearing along the borders between adjacent stripes. It was observed that increasing the resolution of the XCT scanning significantly influenced the mapping of the shape of pores and – to a lesser extent – the recorded porosity. The comparison of geometry deviations after numerical simulation and tensile test for FE models obtained with different XCT resolutions allowed to show differences in the geometry of experimentally and numerically damaged test samples.

Exemplification of Detecting Gas Turbine Blade Structure Defects Using the X-ray Computed Tomography Method

X-ray computed tomography is more often applied in non-destructive testing the quality of construction elements significantly crucial for reliability and safety of device elements, machines and complex industrial systems. This article describes the computed tomography (CT) system used to inspect the technical condition of turbine blades of the aircraft engine. The impact of the experimental conditions on the correctness of the obtained results was determined. The appropriate selection of parameters for the experiment was given, and the correct test results of gas turbine blades were presented. Failures, manufacturing defects, material deviations of nickel-cobalt alloyed blades were identified. The thickness of walls was measured in the selected cross-sections with the accuracy of 0.01 mm, and selected manufacturing defects of cooling passages were diagnosed. It was demonstrated that the application of the CT system allows for detailed non-destructive inspection of the technical condition of machine parts. The test results proved that the X-ray computed tomography could be applied in the production and repairs of machines.