X-ray Computed Tomography Scanning Research Articles

Evolution trend and weakening mechanism of mode-I fracture characteristics of granite under coupled thermo-hydro-mechanical and thermal treatments

Understanding the fracture behavior and fracture-morphology evolution of granite after coupled thermo-hydro-mechanical (THM) environment is important for many geotechnical projects. Previous studies mostly focused on the fracture-response mechanism of rocks after a thermal treatment, whereas only a few studies were conducted on the fracture toughness, fracture-process-zone (FPZ) size, and fracture-morphology evolution of granite after the THM multifield coupling. Therefore, a coupled THM damage treatment (i.e., THM-induced damage) of granite was carried out using a self-developed, high-temperature, and high-pressure multifield coupling triaxial universal tester. Subsequently, a series of test methods was employed, which included the full-field 3D digital-image correlation technique (real-time tracking of the strain/displacement field on the specimen surface), X-ray computed tomography scanning technique (to obtain the microdamage structure inside the specimen), and 3D laser scanner (to obtain the section morphology of the specimen). These methods were employed to study the response mechanism of mode-I fracture of a granite specimen (fracture toughness, fracture trajectory, FPZ size, and fractal dimension of the section topography). Furthermore, to elucidate the correlation between the coupled THM induced damage and fracture characteristics of granite, the same experimental test was also carried out on the granite using a thermal treatment. The result show that the evolution pattern of the fracture and morphological parameters of granite after the coupled THM treatment was different from that using only the thermal treatment, and the value of these physical parameters fluctuated at approximately 400 °C–500 °C. This is due to the limitation of the triaxial stress on the thermal expansion (25 °C–300 °C), competitive effect of “opening” and “closing” of micropores/microcracks (400 °C–500 °C), and deterioration of the coupled THM field (600 °C–650 °C). The results provide insights and theoretical guidance for high-temperature underground rock-mass engineering such as deep nuclear-waste reservoir.

Anthracene Single-Crystal Scintillators for Computer Tomography Scanning.

X-ray imaging and computed tomography (CT) technology, as the important non-destructive measurements, can observe internal structures without destroying the detected sample, which are always used in biological diagnosis to detect tumors, pathologies, and bone damages. It is always a challenge to find materials with a low detection limit, a short exposure time, and high resolution to reduce X-ray damage and acquire high-contrast images. Here, we described a low-cost and high-efficient method to prepare centimeter-sized anthracene crystals, which exhibited intense X-ray radioluminescence with a detection limit of ∼0.108 μGy s-1, which is only one-fifth of the dose typically used for X-ray diagnostics. Additionally, the low absorption reduced the damage in radiation and ensured superior cycle performance. X-ray detectors based on anthracene crystals also exhibited an extremely high resolution of 40 lp mm-1. The CT scanning and reconstruction of a foam sample were then achieved, and the detailed internal structure could be clearly observed. These indicated that organic crystals are expecting to be leading candidate low-cost materials for low-dose and highly sensitive X-ray detection and CT scanning.

Section Area Estimation Methods for Determining the Mechanical Properties of Laser Powder Bed Fusion Thin Wall Structures

A critical aspect of generating mechanical property data is the accurate estimation of the cross-sectional area of the specimen being tested for computing stress. This ordinarily trivial matter assumes greater significance in the context of thin wall structures (defined here as less than 2 mm thick) fabricated using the laser powder bed fusion process commonly used in metal additive manufacturing. This is primarily on account of the significant surface roughness associated with additively manufactured parts as well as due to variations in cross-sectional area across the gauge. In this work, the thin-wall measurement capabilities of four different metrologies are examined – standard micrometer, point micrometer, blue light 3D scanning, and x-ray computed tomography (XCT) scanning. Seven specimens covering a thickness range of 0.3 to 2 mm are measured by each of the metrologies and tested mechanically, with stress-strain curves derived using the different section area estimates from these metrologies. XCT scanning is chosen as the baseline on account of having the highest resolution of the metrologies under study. Deviations from XCT scanning are established, showing that the standard micrometer is a poor method of choice, particularly at low thicknesses, but that point micrometer measurements are within 5% of XCT measurements across all thicknesses. Blue light scanning is also shown to be a reliable measurement method at all but the lowest thickness, and is also used to estimate the coefficient of variation (CV) in section area within each specimen, showing that the CV rises sharply as specimens get thinner. This paper thus demonstrates, for the first time, the validity of using a point-micrometer for section area estimation, while also showing how variations in section area for thin specimens can contribute to initiation of failure at lower strengths, and thus at least in part explain mechanical debits observed with reductions in thickness.

Experimental apparatus for resistivity measurement of gas hydrate-bearing sediment combined with x-ray computed tomography.

Natural gas hydrate has sparked worldwide interest due to its enormous energy potential. Geophysical surveys are commonly used in gas hydrate exploration, and resistivity logging plays an important role in this field. Nevertheless, the electrical response mechanism as a result of the gas hydrate growth in sediment is not well understood. This study develops an apparatus for the in situ resistivity testing of gas hydrate-bearing sediment combined with x-ray computed tomography scanning. Using this equipment, the gas hydrate samples can be synthesized under high-pressure and low-temperature conditions. The sample resistivities of three different layers can also be measured in situ during the gas hydrate formation. Moreover, x-ray computed tomography scanned gray images are acquired, which can be used to calculate the saturation and analyze the microscopic distribution of gas hydrate. A series of experiments are performed to validate the feasibility of the apparatus. The results show that the sample resistivity shows three distinct stages of variation as the gas hydrate grows. The most sensitive saturation range to the electrical response is ∼10.50%-22.34%. Very few gas hydrate particles will not significantly change the pore connectivity. By contrast, too many gas hydrate particles will hinder the pore network blocking. Both situations will not result in a significant change in resistivity.

Unravelling biodegradation and toxin release kinetics of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-based biocomposites in a simulated rumen environment: A preliminary study

The development of completely digestible rumino-reticulum devices (RRDs) able to slowly release natural toxins in bovine rumen has been proposed to be a sustainable strategy to control Pimelea poisoning among graving cattle caused by toxic grasses endemic in Australia. Three pioneer biocomposites were extruded from the plant particles of the toxic plant Pimelea trichostachya and the biodegradable biopolymer poly-3-hydroxybutyrate-co-1 mol% 3-hydroxyvalerate (PHBV), with or without sucrose and starch as pore forming agents. To understand the biodegradation and toxin release mechanisms of these emerging materials in a rumen environment, these biocomposites were incubated, along with pristine PHBV as reference, in an in vitro anaerobic bioreactor simulating the rumen fermentation process. It was shown that surface erosion was the dominant pattern of biodegradation for all the biocomposites, through a series of comprehensive analyses on micro- and macroscopic scales. X-ray computed tomography scanning (μ-CT) observations and the biodegradation kinetic modelling results confirmed that porogen leaching introduced more interior surface areas but did not accelerate the biodegradation rate significantly. Competing phenomena of toxin adsorption and release from the biocomposites were also revealed. This study not only provided guidance in further tailoring the toxin release behaviours and assessing the end-of-life of these biocomposites, but could also be beneficial for constructing PHBV based-RRDs with other purposes.

Characterization of asphalt mixture using X-ray computed tomography scan technique after freeze-thaw cycle and microwave heating

• Recommend the optimum healing moment of different asphalt mixtures suffering from moisture damage. • HEL and SRL are introduced to compare the self-healing properties of different asphalt mixtures. • There are three moisture damage and microwave healing modes of asphalt mixtures on pores. • Valid pores and invalid pores are proposed to characterize the internal pores of asphalt mixtures. • The self-healing properties and characterization of different asphalt mixtures are compared. Microwave heating technology could heal micro-cracks caused by freeze-thaw (F-T) cyclic damage. The main objectives were to recommend the optimum heating moment and evaluate the difference between two typical mixtures during F-T cycle and microwave heating based on microstructure. To this end, cyclic F-T split tests and microwave heating tests were conducted to determine the best heating moment. In addition, the internal structure was scanned using X-ray computed tomography and evaluated using digital image processing. The results indicated that the optimum timing to heal two different asphalt mixtures (AC-13 and OGFC-13) occurred when the degrees of moisture damage were 39.8% and 42.4%, respectively. AC-13 exhibited better heating uniformity, and OGFC-13 exhibited better heating transferring. Moreover, F-T damage and microwave heating could change the internal structure: three types of moisture damage were seen in the voids: pore generation, connections, and expansion; pore number, porosity, pore area, and equivalent diameter first increased after the F-T cycles and then decreased after microwave heating, but the effect for OGFC-13 was more obvious; The F-T cycles mainly increased the number of valid pores, and microwave healing mainly increased the number of invalid pores; The damage and healing process of AC-13 and OGFC-13 mainly occurred on the 0.15–1.18 mm and 0.15–4.75 mm pores. This research could contribute to maintenance cost savings and revelation of F-T damage and microwave healing mechanism.

Process-aware optimisation of lattice structure by electron beam powder bed fusion

Lattice structures are 3D open topologically ordered geometries that repeat an elementary cell in a predefined 3D space. Struts connected in specific nodes define the cell. Lattice structures are typical geometries that represent the design freedom unlocked by additive manufacturing (AM) and are unachievable with traditional processes. By tuning the morphometric parameters of the cell, its mechanical response can be significantly altered. Because of that, an accurate understanding of the process capabilities is crucial for achieving the nominally designed properties. Considering an electron beam powder bed fusion process, in this work, the same nominal lattice structure is produced under different processing conditions to determine the relationship between the process parameters, the actual cell morphometric parameters, and its mechanical response. Strut dimension, relative density and cross-section are measured using advanced X-ray computed tomography scanning analyses. Uniaxial compressive tests describe the mechanical performance. Inferential and descriptive statistical analyses are applied to investigate the effect of process parameters on the actual strut dimension and infer regression models. The results show that even slight variations of the process parameters significantly affect the morphometric structure parameters that result deviated from the nominal ones. The work demonstrates a strong correlation between all morphometric structure parameters and corresponding mechanical properties. The obtained regression model can predict the strut dimension from the process parameters, which can be then used to estimate the actual relative density and strut size. With this control and without any complex design procedure, a fine-tuning of process parameters allows a precise 3D spatial and localised control of structure properties to produce functionalised structures directly.

Three-dimensional failure behaviour of L-shaped laminated composite with wrinkles and defects

In this paper, three-dimension failure behaviour of L-shaped composite beam with manufacturing defects was studied under four-point bending test condition. First, X-ray computed tomography scan was performed for L-shape laminated composite beam specimen to detect manufacturing defects such as voids, pre-delamination, and wrinkles or ply waviness. The scan images were then converted to three-dimensional volumetric entity through image processing, from which finite element mesh was generated with the detected defects directly incorporated. Next, three-dimensional progressive failure analysis was performed for the finite element model of the L-shaped laminate composite simulating four-point bending test condition with delamination and matrix failure in 90 degree plies accounted for by using cohesive zone modelling. The predicted maximum load was well matched to that obtained by tests validating the analysis modeling. Then a series of parametric studies were performed to investigate the effect of defect size and location on the failure load and delamination propagation pattern. It was found that the maximum load reduction was the largest when the pre-defect was located at the center of the symmetrical portion of the L-beam. In addition, the maximum load and delamination development behavior varied significantly depending on the interlayer and in-plane position of the pre-defect.

Effects of fast x-ray cone-beam tomographic measurement on dimensional metrology

X-ray computed tomography (XCT) is increasingly used for dimensional metrology, where it can offer accurate measurements of internal features that are not accessible with other techniques. However, XCT scanning can be relatively slow, which often prevents routine uptake for many applications. This paper explores the feasibility of improving the speed of XCT measurements while maintaining the quality of the dimensional measurements derived from reconstructed volumes. In particular, we compare two approaches to fast XCT acquisition, the use of fewer XCT projections as well as the use of shortened x-ray exposure times for each projection. The study shows that the additional Poisson noise produced by reducing the exposure for each projection has significantly less impact on dimensional measurements compared to the artefacts associated with strategies that take fewer projection images, leading to about half the measurement error variability. Advanced reconstruction algorithms such as the conjugate gradient least squares method or total variation constrained approaches, are shown to allow further improvements in measurement speed, though this can come at the cost of increased measurement bias (e.g. 2.8% increase in relative error in one example) and variance (e.g. 25% in the same example).

Investigation of Silicon-Based Anodes for Li-Ion Batteries Using X-Rays and Neutron 3D/4D Imaging Techniques

Silicon-based anode materials are one of the most promising approaches to further increase the energy density of lithium-ion batteries. However, current materials are limited by poor cycling stability and rapid capacity fading, mainly caused by the massive volume expansion of Si during lithiation and subsequent strain on the material composite. [1] Furthermore, this electrode swelling also results in continuous solid electrolyte interface (SEI) growth, which hinders the migration of Lithium and leads to permanent capacity loss. [2] [3]To optimize these materials, analytical techniques able to probe the local 3D morphology and Li content are necessary. By applying methods such as neutron computed tomography (NCT), X-Ray computed tomography (XCT) and synchrotron scattering micro-tomography (SMT) structural ageing and changes in the distribution of lithium in the various components can be characterized and quantified for different charging states and recharge cycle numbers.This study investigates an anode material based on a dual phase alloy system of amorphous Silicon (a-Si) with crystalline iron silicide (c-FeSi2) and graphite. [4] [5] Li-ion battery coin cells containing this silicon-graphite composite anode material were industrially produced and aged by performing 1, 300, and 700 charge-discharge cycles, corresponding to remaining capacities of 100, 70 and 50 %, respectively. NCT and XCT scans were acquired at the NeXT instrument of the ILL in Grenoble (France) [6], and SMT measurements performed at ID31 of the neighboring ESRF. These datasets were reconstructed and evaluated using specially developed data processing pipelines. By performing multi-modal registration, the NCT and XCT scans were aligned and segmented to combine the complementary datasets and create a 4D model of the Li-ion battery coin cells.Figure 1 shows a sample of the combined NCT (cyan) and XCT datasets (red). Cropped horizontal slices of Li-Ion battery coin cells are depicted side by side with the main components labelled. Comparing one of the highly cycled cells with 50% remaining capacity (top) with the reference cell without electrolyte (bottom), trapped Lithium can be observed in the anode layers, visible as cyan colored blotchy areas in the otherwise dark component. The pixel size is approximately 5 µm.The change of lithium distribution in the components between different cycle numbers and charge states in the attenuation-based tomography techniques of NCT / XCT is quantified by modelling expected attenuation parameters to the observed values. The diffraction-based tomography method of SMT was modeled using expected lattice parameters. From this information, trapped Lithium can be identified and changes in the distribution are analyzed to point out possible degradation and failure mechanisms.We acknowledge financial support from the European Union’s Horizon 2020 research and Innovation program No. 875514 (ECO2LIB) as well as No. 847439 (InnovaXN) under the Marie Skłodowska-Curie grant agreement.[1] S. Tardif et al, https://doi.org/10.1021/acsnano.7b05796 [2] T. Vorauer et al, https://doi.org/10.1038/s42004-020-00386-x [3] P. Kumar et al, https://doi.org/10.1002/smll.201906812 [4] C. Berhaut et al, https://doi.org/10.1021/acsnano.9b05055 [5] C. Berhaut et al, https://doi.org/10.1016/j.ensm.2020.04.008 [6] A. Tengattini et al, https://doi.org/10.1016/j.nima.2020.163939 Figure 1

Polymer Electrolyte Fuel Cell Degradation Investigations Using X-Ray Computed Tomography

On-going research is aimed at commercializing low temperature fuel cell technology systems as zero emission alternatives for automotive applications in order to reduce greenhouse gas emissions and air pollution. These systems use polymer electrolyte fuel cells (PEFCs) to generate electricity via an electrochemical process using hydrogen and ambient air (oxygen) to produce water. Advantages of PEFCs include quick start-up time, low operating temperature, low weight, high efficiency, and relatively simple design. An important area of current research is the identification of factors which affect fuel cell performance degradation during operation and ultimately, its durability. A technique that has yielded new insights in the investigation and identification of failure modes in fuel cells is lab-based X-ray computed tomography (XCT), which is most advantageous due to its on-demand availability. The Fuel Cell Research Laboratory (FCReL) at Simon Fraser University currently operates Canada’s only facility for multi-length scale XCT, comprising of two state-of-the-art laboratory-based XCT scanners from Carl Zeiss X-ray Microscopy (Zeiss Xradia 520 Versa and 810 Ultra) with complementary resolution and field of view capabilities. This unique combination offers unprecedented access to investigations at multi length scales; with an ability to probe fuel cell components at the micro as well as the nano scale. Figure 1 illustrates the fuel cell holder and its orientation with respect to the X-ray beam as well as an exploded view of the miniature fuel cell design.An overview of recent fuel cell degradation investigations at FCReL using the XCT technique will be shown. The XCT based workflow facilitates determination and quantification of material structure and properties changes resulting from degradation stresses associated with operational parameters such as temperature, relative humidity, and voltage. The non-destructive nature of lab-based XCT visualization coupled with the ability to scan the same fuel cell multiple times without inducing damage [1] has enabled detailed studies of fuel cell degradation evolution in four dimensions (3D space, 1D time) [2 - 4]. The new knowledge gained from this procedure has led to root cause identification with respect to membrane and catalyst layer crack initiation and propagation [5 - 7], sealing issues [8,9], and subsequent mitigation toward enhanced fuel cell durability. Acknowledgement This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Canada Research Chairs, and Ballard Power Systems.

Relationship Between Irrigation Thresholds and Potato Tuber Depth in Sandy Soil

Soil disturbance resulting from tuber crop harvesting is a major threat to soil health. The depth of soil intervention is a critical factor that further strengthens the effects of such disturbance and makes harvest one of the most harmful cropping operations. In the case of potato, soil moisture is a determining factor for root and stolon development, hence, a deeper soil intervention may be required at harvest. While potato ranks as the fourth most cultivated crop worldwide, the impact of soil moisture on potato tuber vertical and horizontal distribution has received very little attention. The objective of this study was to evaluate the effects of four soil matric potential thresholds (SMPTs; –10, –20, –30, and –45 kPa) on the spatial (vertical and horizontal) distribution of potato tubers grown in plastic containers filled with sandy soil using an X-ray computed tomography scanner. The results of the experiments conducted in a greenhouse environment suggest that the horizontal distribution of the tubers did not differ significantly across the irrigation treatments. However, a linear relationship between SMPT, and therefore irrigation threshold, and potato tuber depth was observed. In addition, the deepest tuber position was observed under the –10 kPa SMPT, while the tubers were closer to the soil surface under the –45 kPa SMPT, which could lead to a greater preponderance of tuber diseases such as late blight or greening. Thus, potato irrigation events implementing a SMPT between –20 and –30 kPa could reduce the harvest depth, hence, decreasing the negative impacts of soil disturbance on soil structural stability and soil organic carbon degradation while mitigating the impacts of disease as well as reducing fuel costs, greenhouse gas emissions, soil loss and erosion.

Process-induced failure mode transition of compression molded discontinuous carbon fiber composites: From coupon to component level

Discontinuous carbon fiber composites have been reported to be damage tolerant materials with insensitivity to notches and defects. Meso-scale damage mechanisms and crack arresting are responsible for high apparent fracture toughness and pseudo-ductility. This work studies the effect of manufacturing and structure formation on the mechanical behavior of stochastic carbon fiber sheet molding compounds based on thermosetting prepreg platelets with a fiber length of 50 mm. The process–structure–property–performance relationship is analyzed by non-destructive characterization and mechanical bending tests on the component level. Model components of various preform and stack placement scenarios were compression molded to investigate different flow conditions, weld lines and artificially introduced defects. The experimental findings revealed a process-induced failure mode transition from pseudo-ductile to brittle failure behavior. Low-flow scenarios showed a highly non-linear response with large deflection values and high energy absorption. Higher in-mold material flow and weld lines caused brittle failure at significantly lower deflections with a considerable reduction of energy absorbing capacity. Increased material flow also reduced component stiffness and maximum load values. Weld lines exhibited major strength reduction compared to the pristine material configuration. Full-scale and high-resolution X-ray computed tomography scans revealed differences in local fiber orientation state, increased levels of fiber waviness and porosity, as well as asymmetric distribution of defects.

Relationship between fine aggregate size and the air void system of six mortars: I. Air void content and diameter distribution

Precisely determining the characteristics of the air void system in cement-based materials is important in material design and freeze-thaw durability evaluation. X-ray computed tomography (XCT) has been used to characterize air void systems, since it is able to measure the 3D spatial arrangement of the voids. Though the factors influencing air void formation and arrangement have been well-studied, the role of fine aggregate size and gradation has mainly been ignored. In this paper, six mortars were prepared with varying sand size distributions and their air void system quantitatively characterized via XCT. The role of sand size distribution and blended proportions were combined via calculation of the fine aggregate specific surface area (SSA). A linear relationship between SSA and global air void volume fraction was observed, with increasing air void volume fraction as SSA increased (and sand size decreased). The 2D circle diameter distribution was derived from 2D analysis of each XCT slice and the 3D sphere diameter distribution was derived from 3D analysis of the stacked 3D XCT microstructure. The distributions for 2D and 3D were calculated from each other using stereological methods and compared with the original experimental results. All three methods used were in reasonable agreement. The air void size distributions obtained via high resolution (small voxel size, small scan volume) and low resolution (large voxel size, large scan volume) XCT scans compared favorably in a compatible air void size range, which illustrates how the problems of differing XCT resolutions can be resolved.

Multi‐scale characterization of granular media by in situ laboratory X‐ray computed tomography

AbstractInvestigations of biphasic monodisperse soft (rubber) and stiff (glass) particle mixtures under hydrostatic conditions show an interesting behavior with regard to the effective stiffness. P‐wave modulus measured by acoustic wave propagation at ultrasonic frequencies showed a significant decline while more soft particles are added, that is, higher rubber volume fractions, due to a change in the microstructure of the granular medium. However, for small volume fractions of soft particles, it could be observed that the P‐wave modulus is increasing. This result cannot be explained by classical mixture rules or effective medium theories. For the understanding of those effects, a detailed insight into the microstructure of the granular medium is necessary. To gain this information and link it later back to the measured effective mechanical properties, high‐resolution micro X‐ray computed tomography (XRCT) imaging is a well‐established tool. With XRCT imaging, the granular microstructure can be visualized in 3D and characterized subsequently. Combining classical effective characterization methods with XRCT imaging can help to solve a variety of multi‐scale problems. Performing the characterization step in situ, meaning inside the laboratory‐based XRCT scanner, has the advantage that exactly the same samples are mechanically characterized and visualized. To address the mentioned observation above, we designed a low X‐ray absorbing oedometer cell with integrated broadband piezoelectric P‐wave transducers which enables this kind of investigation inside a laboratory‐based XRCT scanner. The focus of this contribution is on the general experimental methodology which can be transferred to other multi‐scale problems. It starts with a description of the image acquisition and ends with the post‐processing of the in situ acquired image data. To demonstrate this, cylindrical samples consisting of the same monodisperse rubber and glass particle mixtures that were studied before under hydrostatic stress conditions are considered. Selected results are presented to explain the single steps.

Investigation on the evolution characteristics of bed porous structure during iron ore sintering

To better understand the evolution characteristics of bed porous structure during iron ore sintering, X-ray computed tomography scanning technology was used to analyze the pore parameters in different areas of the sintering bed. A pore skeleton structure model was established to study the characteristics of the airflow channels in different zones. The absolute permeability of different areas was calculated through simulation, and the corresponding streamline and pressure drop distribution were analyzed. The results show that the porosity of raw material zone, high-temperature zone, and sintered zone increases gradually, which are 37.69%, 46.41%, and 55.57%, respectively. The absolute permeability calculation results of the raw material zone and sintered zones are 792.49 μm2 and 20560.80 μm2, while the tortuosity is 1.77 and 1.45, respectively. Compared with the raw material zone, the flow streamline in the sintered zone is thicker and denser, the airflow resistance and the pressure drop are minor.

Preliminary Planning for Mars Sample Return (MSR) Curation Activities in a Sample Receiving Facility (SRF).

Preliminary Planning for Mars Sample Return (MSR) Curation Activities in a Sample Receiving Facility (SRF).

DETRENDED FLUCTUATION ANALYSIS OF THREE-DIMENSIONAL DATA: APPLICATION TO SOIL X-RAY CT SCANS

In this work, we compare three distinct schemes for detrended fluctuation analysis (DFA) of three-dimensional (3D) [Formula: see text] data sets: (i) an [Formula: see text] set of one-dimensional (1D) DFA runs for each vertical line of length [Formula: see text], (ii) a set of [Formula: see text] two-dimensional (2D) DFA runs for each of the [Formula: see text] planes along the vertical direction, and (iii) a single 3D DFA run. The objective of this work is two-fold: (i) to compare the performance of 1D, 2D, and 3D DFA methods in terms of compatibility as well as the richness of obtained results, and (ii) to demonstrate how these three complementary approaches shed new light on the complexity of the structure of the two real soil samples, through the analysis of grayscale high-resolution X-ray computed tomography scan images.

Anisotropic thermal diffusivity and conductivity in SiC/SiC tubes studied by infrared imaging and X-ray computed tomography

Traditional flash diffusivity evaluation of thermal diffusivity/conductivity of composite tubes require machining of specimens. For a thin-wall tube, this method can only be used to obtain through-thickness transport property. A novel method to evaluate anisotropic thermal diffusivity in a composite tube has been developed. Braided SiC/SiC composite tubes were subjected to a xenon flash heating pulse. A high-speed, high-sensitivity infrared camera was used to measure surface temperature changes as a function of time and nondestructively detect subsurface defects/damages, such as macroscopic pores. Standard reference material (Pyroceram 9606) and curved SiC/SiC composite tube specimens were used to validate thermal diffusivity obtained from infrared imaging. Unlike the traditional method, there is no need prepare special specimens, and thermal diffusivity values in three orientations are obtained after a single flash. A finite element analysis model based on x-ray computed tomography scans was developed to simulate the heat transfer. This technique is significant in assessing thermal conductivity and inspecting the health of ceramic tubes during and after service.

In situ dynamic X-ray imaging of fluid-rock interactions inside tight sandstone during hydraulic fracturing: fluid flow process and fracture network growth

Hydraulic fracturing plays a fundamental role in unconventional hydrocarbon production and the development of enhanced geothermal systems. Thus, studying the fluid flow process and fracture network growth during hydraulic fracturing is necessary to provide guidance for creating and sustaining fracture networks in target reservoirs. The actual formation stress state and hydraulic fracturing process can be simulated in the laboratory for small-scale rock samples in hydraulic fracturing experiments. High-energy industrial X-ray computed tomography (CT) has been used to directly track the fracture propagation in millimeter-scale samples under triaxial stress loading. In this study, a large-scale fracture network with economic benefits for unconventional energy exploitation was the target of the experiment; therefore, centimeter-scale samples were used. A hydraulic fracturing simulation experiment was conducted on tight sandstone by applying triaxial compression and injection pressures. With the assistance of the PEEK core holder and third-generation medical X-ray CT scanner, in situ dynamic X-ray imaging of the fluid-rock interactions inside the sample was conducted for the first time. The fluid-rock interactions and fracture network growth can be dynamically observed, revealing the fluid-rock interactions during the hydraulic fracturing process and how macroscopic failure develops from the microfracture.