Microfocus Computer Tomography Research Articles

Pore-scale deformation characteristics of hydrate-bearing sediments with gas replacement

Gas replacement method enables the simultaneous exploitation of natural gas and the realization of carbon capture, utilization, and storage (CCUS). Safe exploitation of hydrate-bearing sediments (HBS) has garnered significant attention, particularly concerning the engineering geological risks involved. Understanding deformation characteristics during shear after the replacement of HBS is crucial for safe and efficient exploitation. This study employs microfocus computer tomography and digital volume correlation (DVC) to investigate the deformation characteristics of HBS samples with varying replacement percentages. Key findings include: 1. An increase in failure strength of HBS is observed with higher replacement percentages due to improved hydrate cementation and consolidation under confining pressure. 2. DVC analysis shows that narrower radial displacement ranges are associated with increased pore compression, while wider ranges indicate greater particle repositioning. Frequent large axial displacements suggest significant pore compaction, whereas smaller axial displacements indicate particle movement and pore-filling phenomena. 3. The gas replacement process enhances the cementation structure of HBS without altering hydrate saturation, resulting in thinner shear bands and accelerated strain softening with higher replacement percentages. 4. The DVC approach effectively captures volumetric strain and deformation behaviors, offering valuable insights into sediment responses under shear. This study provides a theoretical reference for geological safety evaluation during gas replacement exploitation.

Investigation on multi-parameter of hydrate-bearing synthetic sediment during hydrate replacement process: A in-situ X-ray computed tomography study

Carbon sequestration can be achieved by carbon dioxide replacement in natural gas hydrate exploitation, which reducing greenhouse gas emissions and providing an effective solution to address climate change, while simultaneously protecting the environment and promoting sustainable energy development. Gas replacement can achieve gas exploitation, gas storage, and stability enhancement simultaneously. However, time-varying microstructure evolution of the hydrate-bearing sediment (HBS) during this process remain a large amount of uncertainty. In this study, with microfocus computer tomography, hydrate replacement process is realized using xenon gas to replace krypton hydrate. During this period, the initial hydrate saturation and effective confining pressure were 63 % and 1 MPa respectively, the results were obtained as follows: 1. Hydrate occurrence dynamically adjusted during replacement process due to the “barrier effect” and “diffusion effect”. 2. Dissociated water migration occurred in the sediment, and this induced local hydrate enrichment temporarily and blockages, but the blockages were eventually dredged with the dissociation of the Kr hydrate. 3. The sphericity and surface roughness of the hydrate particles were slightly improved, the pore space connectivity was well enhanced, and both tortuosity and absolute permeability was better strengthened after replacement process, where the absolute permeability was increased by 225.23 %, though the blockage occurrence temporarily weakened this strengthener.

Mechanical and physical characterization of Al2O3–C foam filters produced by distinct processing routes: The importance of the ceramic strut morphology

In this work the influence of the production route and filter dimensions on the mechanical properties of carbon-bonded alumina foam filters was investigated. Features like cold crushing strength and fracture behavior were analyzed and used to compare them. Microfocus computer tomography (μCT) was applied to characterize the geometry of the filters, providing a deep correlation with their fracture behavior. Furthermore, computer-generated filter geometries were used as reference. The results indicated that the centrifugation process is better suited for the production of carbon-bonded alumina filters, and is even more effective when the foam dimensions are increased in the range of those analyzed in this research. Finite element simulations showed the influence of the relative density and strut tapering on the cold crushing strength of filters, providing a correlation between filter structure and its failure mechanism. The attained results provided further insights towards the production of inclusions-free metal parts.

Segmentation of irregular porous particles of various sizes from X-ray microfocus computer tomography images using a novel adaptive watershed approach

This paper presents a novel adaptive watershed algorithm for the segmentation of soil particles in X-ray three-dimensional microfocus computer tomography images. An erosion-filling-dilation technique is also proposed, which is particularly suitable for processing images of highly porous particles. An s-factor is introduced to improve segmentation quality. In the inverse Euclidean distance map of the binary image, the topography in the zone around the local minima defined by this factor is modified. By using an appropriate value of s, the catchment basins and thus the watershed lines can be more realistically defined and it therefore resolves the problem of ill-segmentation. The proposed methods are applied to assemblages composed of highly porous particles with various size distributions, from uniformly graded to well graded or gap graded. The value of s can be decided based on visual examination of the segmentation quality on a sub-volume of the entire scanned domain. It is found that an s-factor that ranged from 0·5 to 0·7 is applicable to all of the studied cases, which enables a balance between under- and over-segmentation. Particulate-scale information including particle size distribution and particle shape characteristics is evaluated from the processed images and the results are compared with other available methods in the literature. Promising results are obtained.

Internal Structure of the Sheared Textile Composite Reinforcement: Analysis Using X-Ray Tomography

X-ray micro computed tomography (Micro-CT) is a non-destructive technique that can provide information on the internal structure of materials. The purpose of micro-CT is to assess the presence of defects as well as characterizing internal structures and potential damage present in the produced part. Simple shear is an interesting deformation mechanism for woven fabric draping. The internal structure change of the carbon fibre twill fabric after shear deformation is chosen as a subject of this paper. Parameters of the mesoscopic internal structure of the woven fabric like cross section, shape, area, and middle line coordinates can be obtained from micro-CT images through image processing procedures. Details of the image data processing for sheared fabric cross sections are discussed. This paper illustrates the possibilities of micro-focus computer tomography in materials research, namely for defining geometrical properties of textile. Image processing is also used for the recognition of fibre direction in the yarns. Described methodology can be applied for determining structure of a fabric, and the results can be used for further micromechanical modelling. Identification of the fibres orientation is important for estimation of the mechanical properties of composites and can be achieved with image processing techniques.

Strain-rate dependence for Ni/Al hybrid foams

Shock absorption often needs stiff but lightweight materials that exhibit a large kinetic energy absorption capability. Open-cell metal foams are artificial structures, which due to their plateau stress, including a strong hysteresis, can in principle absorb large amounts of energy. However, their plateau stress is too low for many applications. In this study, we use highly novel and promising Ni/Al hybrid foams which consist of standard, open-cell aluminium foams, where nanocrystalline nickel is deposited by electrodeposition as coating on the strut surface. The mechanical behaviour of cellular materials, including their behaviour under higher strain-rates, is governed by their microstructure due to the properties of the strut material, pore/strut geometry and mass distribution over the struts. Micro-inertia effects are strongly related to the microstructure. For a conclusive model, the exact real microstructure is needed. In this study a micro-focus computer tomography (μCT) system has been used for the analysis of the microstructure of the foam samples and for the development of a microstructural Finite Element (micro-FE) mesh. The microstructural FE models have been used to model the mechanical behaviour of the Ni/Al hybrid foams under dynamic loading conditions. The simulations are validated by quasi-static compression tests and dynamic split Hopkinson pressure bar tests.

A framework for user driven data management

Scientists within the materials engineering community produce a wide variety of data, with datasets differing in size and complexity. Examples include large 3D volume densitometry files (voxel) generated by microfocus computer tomography (μCT) and simple text files containing results from a tensile test. Increasingly, there is a need to share this data as part of international collaborations. The design of a suitable database schema and the architecture of a system that can cope with the varying information is a continuing problem in the management of heterogeneous data. We present a model flexible enough to meet users’ diverse requirements. Metadata is held using a database and its design allows users to control their own data structures. Data is held in a file store which, in combination with the metadata, gives huge flexibility. Using examples from materials engineering we illustrate how the model can be applied.

X-ray Nano- and Micro-tomography in an SEM

X-ray microfocus computer tomography (μ-CT) is a non-destructive experimental technique that reveals the 3D internal microstructure of the sample under study. The experimental set-up consists of an X-ray source, an X-ray detector, and set in between is a sample that is placed on a rotation stage. With this set-up multiple X-ray projection images can be obtained from the sample at different angles. In between the acquisition of two successive images, the sample is rotated over a small angle, typically between 0.2° and 1°. This set of projection images is then used as input for the reconstruction algorithm, which calculates a reconstruction of the internal microstructure of the sample with (sub-) micrometer sensitivity.

Evaluation of Particle Mixing Process Using X-ray Micro-focus Computer Tomography

Evaluation of Particle Mixing Process Using X-ray Micro-focus Computer Tomography

Morphological Analysis of Slip-Cast Emulsion-Templated Alumina Foams by Microfocus Computer Tomography

Bulk alumina foams were generated by slip casting of suspensions combined with particle-stabilized emulsion droplets as pore templates. Because of the volatile nature of the template, the green foams could be consolidated by sintering without a debinding step. The porous structure of the consolidated foams was analyzed nondestructively using image analysis of microfocus computer tomography (micro-CT) data. The fraction of open and closed pores, as well as the pore sizes and pore size distributions, were calculated from the generated 3D micro-CT datasets and correlated to the applied processing parameters. The anisotropy in the produced structures was assessed and elucidated by a detailed analysis of segmented tomography data. The results indicate that the width of the pore size distribution and the average macropore size, ranging from 225 to 136 μm, depend on the slip rheology. Any anisotropy caused in the structure was linked to the template preparation but is only present in a narrow zone near the bottom of the foams. Although the macroporosity (≥20 μm) was only 24%–31%, tomographic analysis showed that over 90% of these macropores were interconnected through ≥20-μm-diameter windows.

Benefits and Limitations of Cypher Stent‐Based Bifurcation Approaches: In Vitro Evaluation Using Micro‐Focus CT Scan

Intervention for bifurcated lesions is a complex procedure. It could involve a simple main vessel stenting to a comprehensive double stenting of the main vessel and side branch. The clinical outcomes of these different strategies were evidenced by recent results of many randomized trials. However, the mechanisms of technical success or failure from these stenting strategies were not investigated. In this bench study, in vitro silicone bifurcated vessel models were constructed. Stenting from various technical strategies was studied in detail by micro-focus computer tomography.

The connectivity of crystallite agglomerates in low-density firn at Kohnen station, Dronning Maud Land, Antarctica

AbstractIn this study, the three-dimensional (3-D) microstructure of polar firn is investigated by means of X-ray microfocus computer tomography (mCT). Basic topological properties including the Euler and coordination numbers are derived from the reconstructed 3-D volume images. It is shown that sample volumes of about 4 cm3 are representative for polar firn in terms of their connectivity. The connectivity function defined as the change of Euler number with structure size is calculated via image-processing routines. It is used to split the ice phase at small bridges into single crystallite agglomerates. The bond-size distributions and the mean size of the agglomerates are estimated. All μCT measurements were carried out on the uppermost 9 m of a shallow firn core (B35) drilled during the 2005/06 field campaign at Kohnen station, Dronning Maud Land (DML), Antarctica. The results are compared with estimates from classical two-dimensional (2-D) surface section observations. The 3-D approach confirms the linear relationship between coordination number and density which hitherto has only been derived from 2-D observations. Layers of buried snow dunes show a stronger connectivity than layers of moderate crystal size and density. The formation of agglomerates made of crystallites is a common feature of polar firn in DML. It is proposed that the growth of agglomerates leads to reduced critical densities for the transition between the densification regime of grain boundary sliding and plastic deformation.

Evaluation of bone response to titanium-coated polymethyl methacrylate resin (PMMA) implants by X-ray tomography

High-resolution three-dimensional data about the bone response to oral implants can be obtained by using microfocus computer tomography. However, a disadvantage is that metallic implants cause streaking artifacts due to scattering of X-rays, which prevents an accurate evaluation of the interfacial bone-to-implant contact. It has been suggested that the use of thin titanium coatings deposited on polymeric implants can offer an alternative option for analyzing bone contact using micro-CT imaging. Consequently, the aim of the current study was to investigate bone behavior to titanium-coated polymethylmethacrylate (PMMA) implants by micro-CT and histological evaluation. For the experiment titanium-coated PMMA implants were used. The implants had a machined threaded appearance and were provided with a 400-500 nm thick titanium coating. The implants were inserted in the right or left tibia of 10 goats. After an implantation period of 12 weeks the implants were retrieved and prepared for micro-computer tomography (microCT), light microscopy, and X-ray microanalysis. The micro-CT showed that the screw-threads and typical implant configuration were well maintained through the installation procedure. Overall, histological responses showed that the titanium-coated implants were well tolerated and caused no atypical tissue response. In addition, the bone was seen in direct contact with the titanium-coated layer. The X-ray microanalysis results confirmed the light microscopical data. In conclusion, the obtained results proof the final use of titanium-coated PMMA implants for evaluation of the bone-implant response using microCT. However, this study also confirms that for a proper analysis of the bone-implant interface the additional use of microscopical techniques is still required.

In vitro corrosion resistance of porous NiTi intervertebral fusion devices

Porous titanium–nickel (PTN) intervertebral fusion devices, produced by self-propagatinghigh-temperature synthesis, represent an alternative to traditional long-term implantsin the orthopaedic field. PTN promotes tissue ingrowth and has succeededshort-term and long-term biocompatibility in vivo testing. In this in vitro study,the PTN morphology was characterized using microfocus computer tomography(μCT) in order to calculate the active PTN surface. Potentiodynamic polarization testing wasthen performed to evaluate the in vitro corrosion resistance of PTN devices in Hanks’based salt solution. Direct coupling experiments of PTN with Ti6Al4V were alsoperformed in order to establish the galvanic corrosion resistance of PTN intervertebralimplants in the presence of potential Ti6Al4V supplemental fixation devices.Compared to the behaviour of other orthopaedic biomaterials and solid NiTi devices,PTN devices showed a level of corrosion resistance that is comparable to otherNiTi devices and acceptable for the intended orthopaedic application. Furtherimprovement of the corrosion resistance is still possible by specific electrochemical surfacetreatments.

3D visualization of a rock sample, Rotliegend sandstone, Southern Permian Basin: applications for core analysis and petrophysics

A methodology has been developed to visualize and interpret the texture and pore system of rock samples using a virtual reality application. This technique is illustrated using an aeolian sandstone core sample of the Rotliegendes Dethlingen Formation from the Southern Permian basin of northwest Germany. The methodology involves digitizing a series of densely spaced microfocus computer tomography (μCT) images with an appropriate sampling and processing the individual images, which are based on density contrasts, into a volume definition similar to seismic data. Once the volume file has been created the data can be visualized and analysed using virtual reality software. Visualization of scanned core samples has benefits with regards to both the qualitative interpretation of the rock as well as to the quantitative evaluation of the intergranular volumes, cements and pore space. Further advantages exist in terms of the effective communication and collaboration within relevant communities in exploration and production. A key requirement for this technology to be beneficial is calibration of the input slices with rock properties. In terms of the qualitative analysis of the rock, visualization offers the possibility to view slices of the rock samples in any direction. Consequently, bedding planes and fracture planes can be viewed orthogonally even if the physical sample has been cut oblique to these planes. Both slice and transparent volume views are possible, readily revealing the sedimentary and structural features of the rock. Provided that the scanning process has taken place with sufficient resolution, the views can separate grains from cement, matrix and pore space. In addition to the qualitative aspect of visualization, the 3D interpretation capabilities of the software are very valuable. Voxel-based technology allows measurement of grain sizes, cement, matrix and pore space, both in terms of volume as well as geometry. This provides important information in addition, and complementary, to conventional core analysis. In most cases the volume measurements can be expected to be more precise than traditional 2D methods, such as point counting, because they account for the three-dimensional anisotropy of the rock. Stereo-viewing allows pore space to be ‘experienced’ in 3D, offering a better perception and analysis with a view towards hydrocarbon recovery and production strategies. Finally, visualization offers an optimal means to communicate and collaborate, creating a better shared understanding of the relevance of the rock properties within the overall exploration and production evaluation process. Supplementary material: The movie referred to in the article is available at https://doi.org/10.6084/m9.figshare.c.4812969

Individualised, micro CT-based finite element modelling as a tool for biomechanical analysis related to tissue engineering of bone

Load-bearing tissues, like bone, can be replaced by engineered tissues or tissue constructs. For the success of this treatment, a profound understanding is needed of the mechanical properties of both the native bone tissue and the construct. Also, the interaction between mechanical loading and bone regeneration and adaptation should be well understood. This paper demonstrates that microfocus computer tomography (μCT) based finite element modelling (FEM) can have an important contribution to the field of functional bone engineering as a biomechanical analysis tool to quantify the stress and strain state in native bone tissue and in tissue constructs. Its value is illustrated by two cases: (1) in vivo μCT-based FEM for the analysis of peri-implant bone adaptation and (2) design of biomechanically optimised bone scaffolds. The first case involves a combined animal experimental and numerical study, in which the peri-implant bone adaptive response is monitored by means of in vivo μCT scanning. In the second case μCT-based finite element models were created of native trabecular bone and bone scaffolds and a mechanical analysis of both structures was performed. Procedures to optimise the mechanical properties of bone scaffolds, in relation to those of native trabecular bone are discussed.

Towards 3-D petrography: application of microfocus computer tomography in geological science

Microfocus computer tomography (μCT) is a non-destructive technique for imaging internal features within an opaque object. Among the most important recent improvements of μCT is its resolution of about 10 μm in three dimensions, which is much better than that obtainable with medical CT. The advantage of μCT versus classical light microscopy is that three-dimensional petrographical information becomes available. The results from two complementary microfocus instruments are presented. The two instruments can accept different object sizes, ranging from a few millimetres to several centimetres in diameter. As a consequence, downscaling of petrographical features is possible both from medical CT to μCT and within μCT research. Apart from the possibilities of visualisation, attention is paid to the quantitative measurements that can be obtained from μCT research which enables petrographical data to be linked to petrophysical data.

Quantitative coal characterisation by means of microfocus X-ray computer tomography, colour image analysis and back-scattered scanning electron microscopy

Microfocus computer tomography is a non-destructive technique enabling virtual slicing of opaque objects. Stacking several slices enables 3D visualisation of the object. To extract quantitative information, a thorough calibration with data obtained by classical microscopy techniques is needed. Correlation of microfocus computer tomography data with colour image analysis data of reflected-light microscopy and with back-scattered electron microscopy is worked out. SEM EDX is also used to identify mineralogical phases. Compared to former studies, much better resolutions were achieved in the order of 185 μm. Moreover, a dual energy technique is presented allowing the measurement of the density of all components. It is shown that macerals, which are abundant in the studied coal sample (i.e. vitrinite and liptinite in this study), can be quantified by microfocus computer tomography. However, no significant information on other components like pyrite and inertinite, which have surface percentages of less than 2%, could be retrieved from this sample. Finally, a close interrelation between liptinite and clay is demonstrated. With this information a 3D maceral and mineral visualisation and quantification is performed. In the studied sample 23% of the volume of the sample contains 90% of vitrinite together with 10% of another constituent. A 3D coal characterisation is thus possible.

Quantitative analysis of reservoir rocks by microfocus X-ray computerised tomography

Abstract Microfocus Computer Tomography (μCT) is a non-destructive imaging technique that allows visualisation of internal features within non-transparent objects such as sedimentary rocks. With resolution as good as 10 μm in three dimensions, this technique is highly superior to medical CT widely used in geology and material sciences. Superior resolution is achieved by decreasing the X-ray spot size, which allows a decrease in the penumbra effect and an increase in primary magnification by placing the sample close to the X-ray source. Since polychromatic X-ray sources are used, the technique is not free of artefacts. Application of filtering techniques is recommended to circumvent these artefacts and to achieve good quality images for quantitative analysis. Application of a dual energy approach allows quantification of density as well as effective atomic number distribution of internal features. As the technique acquires data in 3D, μCT provides an ideal tool to link 2D thin-section petrography to 3D petrophysical measurements or to be used within an upscaling approach. A number of applications and the use of dual energy density and effective atomic number characterisations are presented. Attention is also paid to some of the limitations of this technique.