Three-dimensional X-ray Imaging Research Articles

Dynamic Behavior of Twisted UHMWPE Yarns

Twisting is an effective method to reduce defects during fabric weaving and improve the impact resistance of the armor material. This study examined the dynamic behavior of twisted ultra-high molecular weight polyethylene (UHMWPE) yarns. Material characterization was conducted using three-dimensional X-ray tomography and scanning electron microscopy (SEM). Dynamic mechanical experiments were carried out on the twisted yarns using a Kolsky bar, with the yarn's failure process captured in real time through high-speed imaging. Additionally, the digital imaging correlation (DIC) technique was used to calibrate the strain measured by the Kolsky bar. Post-fracture analysis was performed using SEM. The effects of twisting extent, strain rate, and gauge length on the dynamic behavior of twisted yarns were studied. It was observed that all twisted yarns underwent elongation, shrinkage, fiber breakage, untwisting, and yarn rupture. Furthermore, as the twisting degree and strain rate increased, and the gauge length decreased, the fracture area became more concentrated. The tensile strength peaked at a twisting degree of 250 t/m and decreased thereafter. Moreover, twisting was found to alter the sensitivity of the yarns' stress–strain curves and tensile properties to the strain rate and gauge length.

Localized corrosion characteristics of Al-Mg-Si aluminum alloy with aging time and pre-delayed aging condition

The effects of single aging, delayed aging and pre-delayed aging treatment on the corrosion resistance of Al-Mg-Si alloy were studied by scanning Kelvin probe force microscopy (SKPFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), three-dimensional X-ray tomography (3D-XRT), confocal laser scanning microscopy (CLSM) and electrochemical measurements. The surface potentials of Al(MnFe)Si, Mg2Si, and Si-rich remnant phases are determined, identifying Al(MnFe)Si phase as the crucial cathodic site for corrosion initiation, and the increase in surface potential implies an accelerated corrosion rate after immersion. The intergranular corrosion susceptibility of the alloy is predominantly influenced by the microstructure caused by aging conditions. The factors affecting corrosion resistance are summarized as (i) adjustment of electrochemical reaction activity by controlling the area fraction of Al(MnFe)Si phase, (ii) the spacing of grain boundary precipitates (GBPs), and (iii) the width of the precipitation-free zone (PFZ). The delayed aging (DA) sample exhibits inferior corrosion resistance due to the continuous GBPs and extended sub-grain boundaries corrosion propagation paths. The pre-delayed aging treatment successfully mitigates the corrosion degree of DA by widening the GBPs spacing and narrowing the PFZ width. This suggests that pre-aging treatment is a potent strategy for enhancing corrosion resistance without compromising the alloy's strength.

ВИНАХІД КОМП‘ЮТЕРНОЇ ТОМОГРАФІЇ І ЙОГО ЗНАЧЕННЯ В ІСТОРІЇ ПУЛЬМОНОЛОГІЇ

Imaging diagnostic methods in pulmonology originate from the discovery of X-rays. Radiography is the first-line tool for chest imaging, but in many cases its capabilities are limited. The aim was to study the history of the invention of computed tomography. Since the radiogram is a two-dimensional summation image of a three-dimensional anatomical structure, there was a need to visualize separate layers of the pathological process. Since 1913, many technical solutions of tomography have been tested. Linear tomography for some time served for the diagnosis of lung pathology, helped to determine the localization more accurately, examine a prevalence, nature and structure of the pathological process, to detect small pathological formations and cavities. But the quality of tomography was not satisfactory. The two outstanding inventors of computed tomography who were awarded the 1979 Nobel Prize in Medicine were not the physicians. Allan McLeod Cormack (Professor and Head of the Institute of Physics at Tufts University, Medford, Massachusetts, USA) was the first to outline the principles of cross-sectional tissue reconstruction in an organ based on X-ray projections in 1963. Godfrey Newbold Hounsfield (Head of Medical Research at Electric and Musical Industries, Middlesex, England) not only reproduced the mathematical algorithms of the technique, but also designed the tomograph and directly participated in its clinical implementation in 1971. Among the developers of the idea of three-dimensional X-ray tomography in 19571958 were the scientists of Kyiv Polytechnic Institute Semyon Tetelbaum and Boris Korenblyum. Key words: radiology, computed tomography, history of pulmonology.

Three-dimensional X-ray imaging of macropore flow

Macropores are known to be important pathways for the rapid transport of water, solutes and colloids in soil. Nevertheless, we still know very little about how the topology and geometry of macropore networks govern water flow configurations and velocities in natural soil. In this study, we aimed at gaining more insight into macropore flow by using X-ray tomography to quantify air–water distributions in the macropore networks of undisturbed topsoil and subsoil columns of a clay soil at varying steady-state flow rates. We observed that while large fractions of the macropore network remained air-filled, the air phase only became entrapped when the irrigation rate was very close to the saturated hydraulic conductivity of the soil. The data enabled us to parameterize a kinematic wave model for water flow following the approach proposed in Jarvis et al. (2017a). Follow-up experiments would be required to evaluate whether these kinematic wave parameters derived by X-ray imaging match with those obtained from outflow measurements. We found that quantitative X-ray imaging of macropore flow through soils still remains a challenging task. We recommend that future experiments are conducted on smaller soil samples to improve image resolution and minimize experimental time spans as well as X-ray image noise and illumination bias. Such experiments could also include 3-D tracer imaging to identify the imaged macropore networks transporting most of the water (i.e. the backbone) at varying steady irrigation rates.

DIGITAL СORE: TEMPERATURE FIELD INFLUENCE ON TWO-PHASE FILTRATION OF FLUIDS IN ROCKS

Link for citation: Katanov Yu.E., Yagafarov A.K., Aristov A.I. Digital сore: temperature field influence on two-phase filtration of fluids in rocks. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 108-118. In Rus. Relevance. Computational fluid dynamics is a powerful tool for studying geological processes. Fluid flow equations in porous media can be solved directly with the resulting three-dimensional X-ray and computer tomographic images. Numerous studies of the geological features of rocks depend on heat transfer in porous materials. These processes include heat conduction in the rock material, convection between matter and the surrounding gas, electrical conductivity, viscous dissipation of fluids, kinetics of chemical reactions, and interfacial heat transfer at the solid/liquid interface. While energy transfer in porous media under conditions of local thermal equilibrium is well studied on the scale of Darcy's law, it is less often considered in porous models. Heat transfer can be accounted for by creating a «heat network» based on a porous network model representing a set of fluid-conducting channels with an appropriate solution to the unified energy balance equation. It is also necessary to take into account convective transfer of thermal energy by the flow of liquid phases (oil, water), each of which is represented by a separate network. Knowing the distribution of the temperature field in the texture of each lithological type of rock, it is possible to determine the probabilistic displacement of the fluid displacement front in the corresponding fluid-conducting space of the rock. Objective: neural network modeling of the effect of the temperature field on the filtration characteristics of hydrocarbons in the fluid-conducting space of rocks. Objects: polymictic sandstones of the Tyumen Formation. Methods. Digital reconstruction of rock texture was performed using artificial intelligence methods and neural networks; neural network algorithms of probabilistic displacement front of two-phase flow (oil, water) were developed in Python programming language; methodical approach to the study of thermal field propagation in rock texture and its influence on two-phase fluid flow was developed using Fourier law, Navier–Stokes equations and similarity criteria of hydrocarbon systems. Results. We developed algorithms for neural network modeling of the temperature field in the fluid-conducting space of a rock (polymictic sandstone) as well as neural network algorithms to estimate the displacement of two-phase filtration front under the corresponding influence of the temperature distribution in the texture of a digital core. The basic mathematical models of these algorithms are outlined. The source code of the algorithms is written in the Python programming language with additional use of non-commercial libraries. The results of neural network modeling have a high degree of reliability, confirmed by experiments with the data obtained in the laboratory of core studies (University of Tyumen, Tyumen), the laboratory of the V.I. Shpilman Research and Analytical Centre for the Rational Use of the Subsoil (Khanty-Mansiysk), laboratory of digital research in oil and gas in the framework of the technological project «Digital core» (Industrial University of Tyumen, Tyumen).

Study on corrosion resistance of passive sealant to Fe-based amorphous coating at atomic-scale

Pore defect elimination is the most effective way to prolong the service life of Fe-based amorphous coating. In this study, the passive sealant (PSG) was successfully prepared by the sol–gel method, and the sealing and passive film continuous repair were completed in one-step. Three-dimensional X-ray tomography (3D-XRT) was used to reveal the PSG penetration depths, which was more than 180 μm and resulted in a significant rising of the coating density. The ferric phosphate film formed on the interface of the sealant/coating changed the semiconductor properties of the passive film. The results of Mott-Shottky test showed that the donor density (Nd) decreased by 5 orders of magnitude, which slowed down the diffusion rate of the point defect of the passive film, and the thickness of the passive film increased from 2.37 nm to 12.04 nm. With the extension of immersion time, the concentration of Fe2O3 and Cr2O3 increased by 183.5 % and 93.5 %, respectively. In addition, the increasing concentrations of Fe3+/Fe2+ and Cr3+/Cr0 also demonstrated the improvement of the coating’s passive ability. This study provides a low-cost and a simple strategy for one-step completion of coating sealing and passive film repair to extending the service life of Fe-based amorphous coating.

Image-based pore-scale modelling of the effect of wettability on breakthrough capillary pressure in gas diffusion layers

Wettability design is of crucial importance for the optimization of multiphase flow behaviour in gas diffusion layers (GDLs) in fuel cells. The accumulation of electrochemically-generated water in the GDLs will impact fuel cell performance. Hence, it is necessary to understand multiphase displacement to design optimal pore structures and wettability to allow the rapid flow of gases and water in GDLs over a wide saturation range. This work uses high-resolution in situ three-dimensional X-ray imaging combined with a pore network model to investigate the breakthrough capillary pressure and water saturation in GDLs manufactured with different mass fractions of polytetrafluoroethylene coating: 5, 20, 40, and 60%, making them more hydrophobic. We first demonstrate that the pore network extraction method provides representative networks for the fibrous porous media examined. Then, using a pore-network flow model we simulate water invasion into initially gas-filled fibrous media, and analyze the effect of wettability on breakthrough capillary pressure and water saturation. With an appropriate pore-scale characterization of wettability, a pore network model can match experimental results and predict displacement behaviour.

Investigation on pitting corrosion mechanism of the Fe-based amorphous alloy coating by three-dimensional X-ray imaging at micro-scale

Few work have been performed regarding the quantitative characterization of three-dimensional (3D) pitting corrosion process directly, although the corrosion behaviors and the passivation film stability of metals in various solutions have been studied heavily. The reported work quantitatively characterized the 3D pitting corrosion of the Fe-based amorphous alloy coating (Fe-based AAC) via X-ray micro-computed tomography (X-ray micro-CT) and further elucidated the mechanism of its pitting corrosion. Moreover, the microstructure and electrochemical performance of the Fe-based AAC have also been explored. The results showed that the targeted thermal sprayed Fe43Cr20Mo10W4C15B6Y2 coating was prone to be corroded with the increase of the hydrogen ion concentration, i.e. higher hydrogen ion concentration leads to poorer corrosion performance of the Fe-based AAC. The X-ray micro-CT results revealed that the pits in the Fe-based AAC initially nucleated below the pitting potential, and they also generated in the over-passivation stage. Furthermore, it was found that the corrosive medium does not penetrate into the coating/substrate interface, and the deduced corrosion mechanism from the findings was also discussed.

(Invited) Interaction and Transformation of Defects during Sodium-Ion Intercalation

Non-equilibrium defects often dictate macroscopic functional properties of materials. In energy materials, dislocations and planar defects significantly modify reversibility and kinetics. Nevertheless, transient imperfections briefly appearing during ionic transport have been challenging to capture, limiting understanding of their life cycle and impact. I will present our recent operando x-ray diffraction, x-ray nanoimaging, and resonant x-ray scattering results in sodium-ion intercalation compounds. Three-dimensional coherent x-ray imaging reveals the transformation and self-healing of a metastable domain boundary, glissile dislocation loop, and stacking faults. I will also discuss structure-selective x-ray spectroscopy, which allows us to link the long-range order with redox reactions in layered oxides during intercalation. The presence of high dimensional defects in energy materials observed with operando nanoimaging suggest their abundance and highlights the importance of defect engineering for developing next-generation energy solutions.

Primary drainage and waterflood capillary pressures and fluid displacement in a mixed-wet microporous reservoir carbonate

A porous plate technique was developed to measure capillary pressure during both primary drainage and waterflooding in a reservoir carbonate rock sample. During primary drainage, a water-wet ceramic disc at the end of the sample allowed brine to be displaced but prevented the escape of oil while oil was injected at a sequence of increasing pressures. Saturation was measured using high-resolution three-dimensional X-ray imaging from the differences in greyscale (X-ray adsorption) between dry, partially-saturated and completely-saturated images. A two-step displacement process was observed, with the resolvable macro-pores displaced by oil followed by invasion into unresolved micro-porosity with a variation of two orders of magnitude in capillary pressure. The sample was then exposed to crude oil to render some of the solid surfaces oil-wet. A small amount of spontaneous imbibition (displacement at a positive capillary pressure) was observed in micro-porosity. Then an oil-wet porous plate was added to the outlet, so that water could be injected at a sequence of increasing pressures while only oil could escape. As expected, the oil-wet macro-porosity was displaced by brine at a low capillary pressure with a magnitude similar to that seen during drainage (but of opposite sign). Remarkably though the displacement of oil from micro-porosity occurred at a capillary pressure approximately an order of magnitude lower than in drainage, implying the existence of mixed-wettability with fluid menisci that are approximately minimal surfaces. The work demonstrates that in mixed-wet media displacement of oil from micro-porosity can occur at much lower capillary pressures that would be estimated from primary drainage results using the calculated pore size distribution.

Measuring cardiomyocyte cellular characteristics in cardiac hypertrophy using diffusion-weighted MRI.

This paper presents a hierarchical modeling approach for estimating cardiomyocyte major and minor diameters and intracellular volume fraction (ICV) using diffusion-weighted MRI (DWI) data in ex vivo mouse hearts. DWI data were acquired on two healthy controls and two hearts 3 weeks post transverse aortic constriction (TAC) using a bespoke diffusion scheme with multiple diffusion times ( ), q-shells and diffusion encoding directions. Firstly, a bi-exponential tensor model was fitted separately at each diffusion time to disentangle the dependence on diffusion times from diffusion weightings, that is, b-values. The slow-diffusing component was attributed to the restricted diffusion inside cardiomyocytes. ICV was then extrapolated at using linear regression. Secondly, given the secondary and the tertiary diffusion eigenvalue measurements for the slow-diffusing component obtained at different diffusion times, major and minor diameters were estimated assuming a cylinder model with an elliptical cross-section (ECS). High-resolution three-dimensional synchrotron X-ray imaging (SRI) data from the same specimen was utilized to evaluate the biophysical parameters. Estimated parameters using DWI data were (control 1/control 2 vs. TAC 1/TAC 2): major diameter-17.4 m/18.0 m versus 19.2 m/19.0 m; minor diameter-10.2 m/9.4 m versus 12.8 m/13.4 m; and ICV-62%/62% versus 68%/47%. These findings were consistent with SRI measurements. The proposed method allowed for accurate estimation of biophysical parameters suggesting cardiomyocyte diameters as sensitive biomarkers of hypertrophy in the heart.

Attentional Ptycho-Tomography (APT) for three-dimensional nanoscale X-ray imaging with minimal data acquisition and computation time

Noninvasive X-ray imaging of nanoscale three-dimensional objects, such as integrated circuits (ICs), generally requires two types of scanning: ptychographic, which is translational and returns estimates of the complex electromagnetic field through the IC; combined with a tomographic scan, which collects these complex field projections from multiple angles. Here, we present Attentional Ptycho-Tomography (APT), an approach to drastically reduce the amount of angular scanning, and thus the total acquisition time. APT is machine learning-based, utilizing axial self-Attention for Ptycho-Tomographic reconstruction. APT is trained to obtain accurate reconstructions of the ICs, despite the incompleteness of the measurements. The training process includes regularizing priors in the form of typical patterns found in IC interiors, and the physics of X-ray propagation through the IC. We show that APT with ×12 reduced angles achieves fidelity comparable to the gold standard Simultaneous Algebraic Reconstruction Technique (SART) with the original set of angles. When using the same set of reduced angles, then APT also outperforms Filtered Back Projection (FBP), Simultaneous Iterative Reconstruction Technique (SIRT) and SART. The time needed to compute the reconstruction is also reduced, because the trained neural network is a forward operation, unlike the iterative nature of these alternatives. Our experiments show that, without loss in quality, for a 4.48 × 93.2 × 3.92 µm3 IC (≃6 × 108 voxels), APT reduces the total data acquisition and computation time from 67.96 h to 38 min. We expect our physics-assisted and attention-utilizing machine learning framework to be applicable to other branches of nanoscale imaging, including materials science and biological imaging.

Hierarchically guided in situ nanolaminography for the visualisation of damage nucleation in alloy sheets

Hierarchical guidance is developed for three-dimensional (3D) nanoscale X-ray imaging, enabling identification, refinement, and tracking of regions of interest (ROIs) within specimens considerably exceeding the field of view. This opens up new possibilities for in situ investigations. Experimentally, the approach takes advantage of rapid multiscale measurements based on magnified projection microscopy featuring continuous zoom capabilities. Immediate and continuous feedback on the subsequent experimental progress is enabled by suitable on-the-fly data processing. For this, by theoretical justification and experimental validation, so-called quasi-particle phase-retrieval is generalised to conical-beam conditions, being key for sufficiently fast computation without significant loss of imaging quality and resolution compared to common approaches for holographic microscopy. Exploiting 3D laminography, particularly suited for imaging of ROIs in laterally extended plate-like samples, the potential of hierarchical guidance is demonstrated by the in situ investigation of damage nucleation inside alloy sheets under engineering-relevant boundary conditions, providing novel insight into the nanoscale morphological development of void and particle clusters under mechanical load. Combined with digital volume correlation, we study deformation kinematics with unprecedented spatial resolution. Correlation of mesoscale (i.e. strain fields) and nanoscale (i.e. particle cracking) evolution opens new routes for the understanding of damage nucleation within sheet materials with application-relevant dimensions.

Steady-state three-phase flow in a mixed-wet porous medium: A pore-scale X-ray microtomography study

We use three-dimensional X-ray imaging to investigate steady-state three-phase flow in a mixed-wet reservoir rock, while measuring both relative permeability and capillary pressure. Oil occupied the smallest pores, gas the biggest, while water occupied medium-sized pores. We report a distinct flow pattern, where gas flows in the form of disconnected ganglia by periodically opening critical flow pathways. Despite having capillary-controlled displacements, a significant fraction of the pore space was intermittently occupied by gas-oil and oil-water phases. Both types of intermittency occurred in intermediate-sized pores. Gas mainly displaces oil, and oil displaces water as the gas flow rate is increased, while oil displaces gas, and water displaces oil as gas flow is decreased. At the resolution of the images, no detectable gas was trapped in the rock due to its mixed-wettability which prevents either oil or water completely surrounding gas, suppressing snap-off and capillary trapping, which has significant implications for the design of gas storage in three-phase systems.

Autotransplantation of a horizontally oriented fragment of the root of a removed tooth to preserve alveolar tissues

To develop a method to contain atrophy of the alveolar bone and surrounding soft tissues in the area of many cortical teeth in the first 3 months after removal for subsequent installation of a dental implant. A description of a method for containing atrophy of the alveolar bone and surrounding soft tissues after removal of the first molar of the mandible 3 months after tooth extraction is presented. The method consists in closing the mouth of the well with a horizontally oriented fragment of the root of the removed tooth with a preserved section of the ligamentous apparatus. An X-ray assessment of bone restoration in the lumen of the well was carried out according to the Hounsfield coefficient and an assessment of the condition of soft tissues in the area of surgery 3 months after removal. For histological assessment of bone maturity, bone was taken from the implantation area 14 weeks after tooth extraction. The technique allowed to preserve the quality of soft tissues close to the original; on three-dimensional X-ray images in the lumen of the well, bone restoration sufficient for the installation of a dental implant is diagnosed, the zonal value of the Hounsfield coefficient is more than 300 units; histologically, a well-developed network of coarse-fibrous trabeculae is determined with the beginning of reconstruction into lamellar bone, regeneration of the alveolar process occurs by intramembranous ossification. The proposed technique contributes to the preservation of the qualities of the marginal gum in the healing zone after tooth extraction and the formation of sufficient bone maturity in the lumen of the well.

Holes in the tundra: Invasive earthworms alter soil structure and moisture in tundra soils

Human introductions have resulted in earthworms establishing in the Arctic, species known to cause cascading ecosystem change. However, few quantitative outdoor experiments have been performed that describe how these soil modifying earthworms are reshaping structures in tundra soils. In this study, we used three-dimensional (3-D) X-ray images of soil cores (approximately 10 cm diameter, 20 cm height, N = 48) to assess how earthworms (Aporrectodea sp. and Lumbricus sp.) affect soil structure and macropore networks in an outdoor mesocosm experiment that lasted four summers. Effects were assessed in both shrub-dominated (heath) and herb-dominated (meadow) tundra. Earthworms almost doubled the macroporosity in meadow soils and tripled macroporosity in heath. Interestingly, the fractal dimension of macropores decreased in response to earthworm burrowing in both systems, indicating that the presence of earthworms reduced the geometric complexity in comparison to other pore-generating processes active in the tundra. Observed effects on soil structure occurred along with a dramatically reduced soil moisture content, which was observed the first winter after earthworm introduction in the meadow. Our findings suggest that predictions of future changes in vegetation and soil carbon pools in the Arctic should include major impacts on soil properties that earthworms induce.

Insight into contact forces in crushable sand using experiments and predictive particle-scale modelling

In this paper, an attempt is made to predict the evolving statistics of inter-particle contact forces during comminution using grain-scale computational modelling. A validation is first carried out by creating a one-to-one virtual avatar of an Ottawa sand specimen from three-dimensional X-ray tomography with level sets and comparing the data from an oedometric test to the model's prediction. The predictive capabilities are confirmed by comparing the constitutive response, grain size distribution and changes in particle shapes in both the experiment and model. Once validated, the predicted contact forces and particle stresses are investigated. It is found that the largest particles experience the largest forces. Despite larger particles being weaker on average, many survive because they are on the stronger side of the particle strength distribution and also have a higher coordination number producing a more isotropic stress state in the particle. These highest forces are largely aligned with the specimen axis, demonstrating that larger particles provide the strength in the loading direction. Meanwhile forces in the radial direction are more broadly distributed, indicating that small particles play a significant part in providing radial stability.

3D in situ study of damage during a ‘shear to tension’ load path change in an aluminium alloy

A load path change (LPC) from shear to tension has been studied for a recrystallized 2198 T8 aluminium alloy sheet material by three-dimensional (3D) X-ray imaging combined with image correlation and interpreted by complementary 3D finite element (FE) simulations. A cross-shaped specimen was designed for the non-proportional loading and multiscale study. The effect of the LPC on the formability and related strain localisation, damage and failure was investigated and damage mechanisms could be clearly identified. The macroscopic tension stretch to fracture, measured by an optical extensometer during the shear to tension test, was reduced by about 20% compared to the proportional tension test. Damage, measured by in situ laminography imaging at μm-scale resolution, has interestingly already been found under shear, and was quantified as surface void fraction during the LPC. Strain was measured inside the material and at the mesoscale by 2D digital image correlation (DIC) on projected volume data, using the (natural) intermetallic particle contrast present in the 3D laminographic data. An accumulated equivalent strain definition, suited for the description of non-proportional loading, has been applied to the DIC data and FE simulations, indicating good agreement between both. On the microscopic scale, damage was seen to nucleate under shear load in the form of flat cracks, of similar width as the grain size, and in the form of cracks inside intermetallic particles. This damage subsequently grew and coalesced during tensile loading which in turn led to final fracture.

Synchrotron 4D X-Ray Imaging Reveals Strain Localization at the Onset of System-Size Failure in Porous Reservoir Rocks

Understanding the mechanisms of strain localization leading to brittle failure in reservoir rocks can shed light on geomechanical processes such as porosity and permeability evolution during rock deformation, induced seismicity, fracturing, and subsidence in geological reservoirs. We perform triaxial compression tests on three types of porous reservoir rocks to reveal the local deformation mechanisms that control system-size failure. We deformed cylindrical samples of Adamswiller sandstone (23% porosity), Bentheim sandstone (23% porosity), and Anstrude limestone (20% porosity), using an X-ray transparent triaxial deformation apparatus. This apparatus enables the acquisition of three-dimensional synchrotron X-ray images, under in situ stress conditions. Analysis of the tomograms provide 3D distributions of the microfractures and dilatant pores from which we calculated the evolving macroporosity. Digital volume correlation analysis reveals the dominant strain localization mechanisms by providing the incremental strain components of pairs of tomograms. In the three rock types, damage localized as a single shear band or by the formation of conjugate bands at failure. The porosity evolution closely matches the evolution of the incremental strain components of dilation, contraction, and shear. With increasing confinement, the dominant strain in the sandstones shifts from dilative strain (Bentheim sandstone) to contractive strain (Adamswiller sandstone). Our study also links the formation of compactive shear bands with porosity variations in Anstrude limestone, which is characterized by a complex pore geometry. Scanning electron microscopy images indicate that the microscale mechanisms guiding strain localization are pore collapse and grain crushing in sandstones, and pore collapse, pore-emanated fractures and cataclasis in limestones. Our dynamic X-ray microtomography data brings unique insights on the correlation between the evolutions of rock microstructure, porosity evolution, and macroscopic strain during the approach to brittle failure in reservoir rocks.

Influence of post-processing on very high cycle fatigue resistance of Inconel 718 obtained with laser powder bed fusion

The pore defects and surface roughness derived from additive manufacturing restrict applications in the production of ultra-long service time parts. Due to the high sensitivity of very high cycle fatigue (VHCF) resistance to defects, smaller defects may also become potential crack initiation sites. To remove these defects and consequently improve fatigue strength, three different post-processing routes, hot isostatic pressing (HIP, 1160 °C/1500 bar/3h ± 30 min), machining, and their combinations, are employed on samples in this research. Three-dimensional X-ray tomography (3D-XRT) shows that pores larger than 25 μm in diameter are mainly located in the “macropore-rich layer” with 300 μm thickness below the surface. HIP can effectively close the pores, but this does not translate into an increase in fatigue performance, which is attributed to the increased roughness. Machining with a certain depth can significantly reduce the surface roughness and remove the “macropore-rich layer.” Therefore, it can improve fatigue resistance. The co-effect of HIP and machining is confirmed to be the most effective solution to improve fatigue resistance. Taking the depth-width ratio of the micro-depression as the characteristic size of the surface roughness, it found that the fatigue life is closely related to the characteristic size of the micro depression. For the pore-induced fatigue failure, the fatigue resistance is related to the pore size and the location. The area of the crack initiation (rough area, abbreviation as RA) is introduced and Areapore/AreaRA is calculated to reflect the pore characterization including the size and location, and the ratio of the pore area to the RA area is found to be have a linear relationship to the fatigue life in single logarithmic coordinates.