X-ray Computed Tomography Observations Research Articles

Creep deformation and cavitation in an additively manufactured Al-8.6Cu-0.4Mn-0.9Zr (wt%) alloy

Creep deformation and cavitation were investigated at 300 ºC in both tension and compression for an additively manufactured Al-8.6Cu-0.5Mn-0.9Zr (wt%) alloy in the as-fabricated state and after various aging treatments (aging at 300 °C/200 h or 350 °C/24 h and overaging at 400 °C/200 h). Creep mechanisms at 300 °C were determined by relating the measured creep response to corresponding microstructural and X-ray computed tomography observations. In compression, alloys in the as-fabricated and two aging conditions exhibited similarly high creep resistance. Overaging (400 °C/200 h) led to substantial coarsening of intragranular θ-Al2Cu precipitates and an expected drop in their Orowan strengthening contribution. In tension, minimum strain rates comparable to those in compression were obtained at any given stress; however, upon accumulation of some plastic strain in the matrix, creep cavities started to form, leading to accelerated tertiary stage creep deformation and rupture. Cavitation occurred exclusively along melt pool boundaries due to locally enhanced diffusion enabled by (ⅰ) large grain-boundary area in adjacent fine-grained zones and (ⅱ) localization of creep strain in nearby heat-affected zones. Although cavity growth was initially diffusion-controlled, its rate was determined by matrix creep rate, consistent with constrained cavity growth mechanisms. This study reveals how microstructural complexities induced by the additive manufacturing process affect the creep and cavitation behavior of Al-Cu-Mn-Zr alloys. The underlying creep and cavitation mechanisms uncovered in this study point to pathways that improve the high-temperature properties of additively manufactured alloys.

Correlating X-ray computed tomography observations with respirometric measurement of aluminium alloy 6063 corrosion under FeCl3 droplets

Corrosion of aluminium alloy 6063-T6 with exposure to simulated steel corrosion products using ferric chloride droplets was investigated. Focus of these experiments was to understand the role of oxygen in the redox process; therefore, samples were exposed to standard atmospheric conditions as well as to oxygen-derived conditions. Respirometric measurements indicate that the hydrogen evolution reaction (HER) is the dominant cathodic reaction. Especially in the initial stages when the corrosion rates are the highest, the HER occurs almost exclusively. At the later stages the oxygen reduction reaction (ORR) barely takes over as the main cathodic reaction. The dissolved volumes and maximum corrosion depths determined with X-ray Computed Tomography (XCT) were more significant for those samples deprived of oxygen. The composition of iron-rich deposits formed consisted of magnetite and maghemite, supporting exposure conditions where reactions were deprived of oxygen.

Filament Structure Analysis of Multifilament MgB2 Wires by Using X-ray CT

We have investigated the filament structure of 18-filament MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wires by using an X-ray computed tomography (CT). For the structural analysis of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> filaments and Nb barriers, we adopted two image processing, the adoptive binarization method and the closing technique, to the series of cross-sectional CT images. After the image processing, we successfully eliminated the effect of several artifacts, such as metal artifacts and beam hardening, and extrapolated the area of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> filaments and Nb barriers. From the images, we made a three-dimensional model of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> filaments and confirmed whether the breakout of the filaments and sausaging phenomena exist or not. Although the broken filaments were not observed, the Nb barrier's break was confirmed in all six inner filaments of the MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire after heat treatment. Moreover, from the statistical distribution analysis, sausaging is more significant in the inner filament than in the outer filament. These results indicate that the X-ray CT observation and advanced image processing is effective in understanding the filament structure in non-destructive ways.

Application of edible coatings composed of chitosan and tea seed oil for quality improvement of strawberries and visualization of internal structure changes using X-ray computed tomography

Edible film composed of chitosan (CH) and tea seed oil (TSO) was prepared by casting method and its physicochemical and structural properties were evaluated. Strawberries were coated with the edible coatings by dipping method and physicochemical properties (weight loss, moisture content, color change, firmness, pH and total soluble solids (TSS)) and internal structures were determined during storage at 2 °C for 24 days. Non-destructive X-ray computed tomography (CT) was used to visualize strawberry internal structure, with CT measured in terms of grayscale (GS) values. As expected, the CH + TSO film decreased water vapor permeability (WVP), with TSO conferring a reduction of 20.83 %. The CH + TSO film decreased moisture content (26.43 %) and water solubility (22.93 %). Incorporation of TSO in CH films significantly increased opacity by 204.76 %, greatly improving the ability to block light. Changes in the surface and structure of the films were obtained by Scanning electron microscopy (SEM), Atomic force microscopy (AFM) and Fourier transform infrared spectroscopy (FTIR) analysis. The properties of CH + TSO film were improved compared to pure CH film. Moreover, the results of storage for 24 days from the coating application to strawberries showed that CH and CH + TSO coatings effectively reduced fruit weight loss; retained firmness, color, moisture content by 86.69 % and 84.93 %, respectively, compared to the control (82.45 %), TSS by 10.22 % and 9.70 %, respectively, compared to the control (9.48 %); delayed pH changes by 3.49 % and 3.54 %, respectively, compared to the control (3.58 %) and ∆E by 8.06 % and 10.31 %, respectively, compared to the control (13.37 %). In particular, the CH and CH + TSO treated strawberries still remained the firmness by 68.36 % and 63.35 %, respectively, compared to the control (59.38 %) and the weight loss of CH and CH + TSO treated samples was 5.83 % and 6.93 %, respectively, compared to 8.11 % for the control. X-ray CT observations revealed that the coating treatments could inhibit the development of voids in the strawberries. These results demonstrate CH and CH + TSO film maintain the physicochemical properties and internal structure of strawberries during storage.

X-Ray Computed Tomography Observations of Multi-Hollowed Fibers Produced by CO&lt;sub&gt;2&lt;/sub&gt; Laser-Heated Drawing

X-Ray Computed Tomography Observations of Multi-Hollowed Fibers Produced by CO&lt;sub&gt;2&lt;/sub&gt; Laser-Heated Drawing

Thermo-hydro-mechanical (THM) evolution law and development of permeability and pore structure of enhanced geothermal systems at ultra-high temperatures

The evolution law and fluctuation mechanism of permeability and pore structure of stimulated reservoirs in hot dry rocks (HDR) under the coupled thermo-hydro-mechanical environment (THM) in ultra-high temperature are of great significance to the production capacity of enhanced geothermal systems (EGS). This paper designed a testing apparatus to take the effects of the THM processes into account by coupling high temperatures and the high triaxial stress. A series of flow tests were performed on a HDR under the coupled THM environment at ultra-high temperatures, i.e., temperature range of 25 to 650°C, triaxial stress of 25 MPa, and seepage pressure of 6 MPa, and ultra-high thermal treatments, i.e., temperature range from 25 to 650°C. Then, the micro-physical parameters of the specimens treated in various conditions were obtained via mercury intrusion porosimetry, thin-section petrography and micro X-ray computed tomography observations. The experimental results show that (1) in the temperature range of 25 to 400°C, the microscopic physical parameters increase monotonously with the increase of temperature. However, the microscopic physical parameters of specimens subjected to the coupled THM condition are lower than those obtained after considering only the thermal treatment, owing to the inhibition effect of the triaxial stress on the thermal expansion; (2) in the temperature range of 400 to 550°C, the microscopic physical parameters subjected to the coupled THM condition fluctuated slightly with the increase of temperature which is due to the strong thermo-elastic-plastic fluidity and the competitive effect of closing and re-opening of pores/fissures; (3) in the temperature range of 550 to 650°C, the microscopic physical parameters are much larger than those obtained after the thermal treatment owing to the severe deterioration of rock mass caused by the coupling THM process. The results obtained is of great significance for the assessment of stability, safety and site selection of high-temperature rock projects such as EGSs.

Correlation Modeling between Morphology and Compression Behavior of Closed-Cell Al Foams Based on X-ray Computed Tomography Observations

In the last decades, great attention has been focused on the characterization of cellular foams, because of their morphological peculiarities that allow for obtaining effective combinations of structural properties. A predictive analytical model for the compressive behavior of closed-cell Al foams, based on the correlation between the morphology of the cellular structure and its mechanical response, was developed. The cells’ morphology of cylindrical specimens was investigated at different steps of compression by X-ray computed tomography, in order to detect the collapse evolution. The structure, typically inhomogeneous at local level, was represented by developing a global virtual model consisting of homogeneous cells ordered in space, that was fitted on the experimentally detected structure at each deformation step. As a result, the main parameters characterizing the two-dimensional cells morphology (equivalent diameter, circularity), processed by the model, allowed to simulate the whole compression stress–strain curve by enveloping those obtained for each step. The model, fitted on the previous foam, was validated by comparing the simulated stress–strain curve and the corresponding experimental one, detected for similar foams obtained by different powder compositions. The effectiveness in terms of an accurate prediction of the compression response up to the final densification regime has been confirmed.

Understanding and suppressing shear band formation in strut-based lattice structures manufactured by laser powder bed fusion

The formation of shear band in metallic lattice structures under compression prompts an unstable stress–strain curve, resulting in a significant reduction in the energy absorption capacity. The development and formation of shear band need to be clarified, and versatile approaches to suppress the shear band are required. In this study, we explored the formation mechanism of shear band using a representative Al–12Si alloy lattice structure, consisting of a simple body-centered cubic (BCC) unit cell manufactured by laser powder bed fusion. The X-ray computed tomography observations of an interruptedly compressed lattice specimen and finite element analyses revealed that the crack initiations in the bent struts under the localized tensile stress trigger the formation of shear band. Accordingly, an attempt was made to fabricate various lattice structures consisting of BCC unit cells with different strut diameter ratios to suppress shear band formation. Finite element analyses revealed relaxed tensile stress inside the struts with the controlled diameter ratios, suggesting the suppressed formation of shear bands; this was demonstrated by compression tests. The present results provide new insights for achieving a stable compressive deformation and high energy absorption capacity of lattice structures.

Effect of the interfacial nanostructure on the interlaminar fracture toughness and damage mechanisms of directly bonded carbon fiber reinforced thermoplastics and aluminum

Carbon fiber reinforced thermoplastics (CFRTPs) are becoming of interest to mass production industries. In this study, we investigated the characteristics of the direct bonding technique to join an aluminum alloy and a CFRTP laminate by fabricating a nanostructure on the aluminum alloy surface. The effect of the nanostructure on the fracture toughness and the damage mechanisms were investigated. The nanostructure improved the fracture toughness by about 2.6 times compared with that without the nanostructure. From observations of the fracture surface, ductile failure of the matrix owing to the nanostructure occurred, suggesting that plastic deformation improved the fracture toughness. From X-ray computed tomography observations, intralaminar failure caused by the nanostructure occurred, which appeared to be a factor for the improved fracture toughness.

Effect of frequency during cyclic hydraulic fracturing and the process of fracture development in laboratory experiments

Cyclic injection in hydraulic fracturing has been reported to reduce the level of induced seismicity compared to the conventional continuous injection. We investigate the evolution of acoustic emission (AE) activity, hydraulic energy, fracture area, and fracture development for cyclic injection schemes with different cycle time durations (td) at a repeated maximum cyclic pressure through laboratory experiments. These test were compared with a case under conventional continuous injection at an injection rate of 50 mm3/s. Pocheon granite samples with an outer diameter of 50 mm, height of 100 mm, and an inner borehole of 8 mm were used. The maximum pressure of 5.5 MPa for each cycle represents approximately 77% of the average breakdown pressure from continuous injection cases. Four td values of 30 s, 60 s, 120 s, and 240 s were selected. The results show an exponential decrease in the number of cycles until failure with increasing td. Similarly, the total number of AEs, the peak AE rate, and the cumulative AE energy also decreased with increasing td. These values contrasted with those for continuous injection which reported the lowest number of AEs, and the highest cumulative AE energy. The td influence was also evident on the AE occurrence, with fewer high amplitude AEs at a high td, and all lower than continuous injection. In general, the hydraulic energy and cumulative AE energy decreased with increased with increasing td, although a slight deviation was related to the total testing time. The fracture areas during cyclic injection reported a positive correlation with the cumulative AE energy. Moreover, detailed analysis of the instantaneous injection rate, and the cumulative AEs suggested a three-stage damage process, which was supported with X-ray computed tomography observations. The second stage was characterized by a steady linear injection rate increase, and its slope correlated with the fatigue life or number of cycles to failure. Finally, based on the injection rate evolution, an interpretation of the damage evolution and fracture onset during cyclic hydraulic fracturing could be made.

Modelling the long-term hydro-mechanical behaviour of a bentonite pellet/powder mixture with consideration of initial structural heterogeneities

The aim of this paper is to investigate the long-term hydro-mechanical behaviour of a highly heterogeneous MX80 bentonite pellet/powder mixture (80/20 in dry mass), which is one of the candidate sealing materials in deep geological repositories. In spite of the operational advantages related to the use of the mixture, structural heterogeneities resulting from the installation process constitute a matter of concern and require special approaches to describe adequately the material behaviour during hydration. In this study, a double structure formulation taking into account the initial structural heterogeneity of the material as well as damage to pellets upon wetting is proposed. The formulation is applied to the modelling of a 1/10 mock-up of Sealex large-scale tests. Hydraulic and mechanical parameters are determined from an extensive laboratory programme carried out on a single pellet of bentonite and on the pellet/powder mixture. To ensure an adequate analysis of the test, the initial heterogeneous structural distribution of the material is determined by image analysis of microfocus X-ray computed tomography observations. The model allows the anisotropic swelling behaviour of the mixture to be satisfactorily reproduced when accounting for the spatial variation of the material's initial porosity. In particular, the long-term (decade) hydro-mechanical behaviour of the mixture can be well described. Detailed analysis of the modelling results demonstrates the existence of dry density gradients at the long term and their influence on swelling pressure anisotropy.

3D-microstructure analysis of compacted Na- and Cs-montmorillonites with nanofocus X-ray computed tomography and correlation with macroscopic transport properties

Microstructural and mass transport properties of compacted Na- and Cs-montmorillonites (Na-MMT and Cs-MMT) with different swelling properties at dry densities of 0.8 and 1.25 Mg m−3 were investigated by combining three-dimensional microstructure analysis using nanofocus X-ray computed tomography (CT), X-ray diffractometry (XRD), and through diffusion measurement of deuterated water (HDO). The X-ray CT and XRD observations indicated that macropores (micrometer- and submicrometer-sized pores) in the dry state of compacted Na-MMT are filled with gel phases, and the grain sizes of clay particles shifted toward smaller values through the saturation and swelling processes. By contrast, no gel phase and no decrease in the grain and pore volumes were observed for saturated Cs-MMT. The De of HDO of Na-MMT was reduced by half compared to that of Cs-MMT owing to the high swelling capacity of Na-MMT and the occupation of macropores with gel phases. The geometrical factors of the macropores, including tortuosity (τ) and geometric constrictivity (δg), in the dry and saturated states of compacted Na-MMT and Cs-MMT were estimated from three-dimensional images of the macropores (and gel phases in saturated Na-MMT) and from the results of their statistical analysis. The estimated geometric factor (δg/τ2) of saturated Cs-MMT was consistent with the corresponding De/εD0 values derived in the HDO diffusion experiment. In the case of Na-MMT, the larger differences between the geometric factors (δg/τ2) evaluated by nanofocus X-ray CT and the De/εD0 values derived by the diffusion tests can be explained by the electrostatic constrictivity factor and the additional geometrical factors in gel phase and interlayer that are smaller than the detection limit of the nanofocus X-ray CT.

Development of the permeability anisotropy of submarine sedimentary rocks under true triaxial stresses

The true triaxial test, which can simulate in-situ stress fields of nature which have different scalar quantity along three principal axes of stress, is the most effective experimental method for obtaining the mechanical and permeability property of rocks under overburden and tectonic stresses. The intermediate principal stress (σ2) is a control on the fracture strength, mechanical behavior and crack distribution of the deformed rocks. Thus, understanding the effect of the stress on the development of permeability anisotropy is crucial. To evaluate the influence of the σ2 on the permeability anisotropy, the permeability measurement lines in the σ1 and σ2 directions were added into an upgraded Mogi-type true triaxial test apparatus. We measured the permeability of Berea sandstone and Amatsu mudstone in the σ1 and σ2 direction under the conditions of true triaxial compression (σ3 < σ2 < σ1) with a constant σ3. In the Berea sandstone, we found that the permeability reduced with increasing mean stress and the magnitude of permeability anisotropy correlated with the intermediate principal stress. Photomicrographs and X-ray computed tomography observations for post-failure Berea sandstones revealed a phenomenon related to permeability: under high σ2 conditions, the fault gouge generated along final fractures causes permeability reduction of σ1 direction. For the Amatsu mudstone is too soft to be subject to brittle deformation. Thus, the development of the permeability anisotropy with increasing mean stresses was more pronounced in the Berea sandstone than the Amatsu mudstone.

X-ray computed tomography observation of multiple fiber fracture in unidirectional CFRP under tensile loading

We investigated the initiation and propagation of fiber fracture in unidirectional (UD) carbon fiber-reinforced composites (CFRPs). The statistical fiber breakage of CFRPs and multiple fiber fracture (the propagation of fiber breakage near the broken fiber) have been studied and observed in specimens after fracture. To date, however, this propagation phenomenon has been rarely observed directly, and investigations have depended mainly on prediction. This direct non-destructive evaluation of fiber fracture phenomenon was performed via X-ray computed tomography of UD CFRPs. Specimens were loaded under various stress levels and imaged at low voltage (20 keV). The fiber breakages were analyzed from these images, which revealed multiple fractures leading to large clusters of broken fibers. Quantitative analyses after image processing revealed a marked increase in the number of multiple fractures, meaning the number of broken fibers in a broken fiber cluster, near the final fracture. Finally, the trend in multiple fractures was compared with the predicted results, showing reasonable agreement.

Fabrication and Compression Properties of Functionally Graded Copper Foam Made Using Friction Powder Sintering and Dissolution

Functionally graded (FG) metal foams have properties that vary with the position, giving them controlled compression deformation behavior with the desired plateau stresses. In this contribution, bilayer FG Cu foams consisting of a high-porosity layer and a low-porosity layer were fabricated and their compression properties were demonstrated. A friction powder sintering process based on the sintering and dissolution process was employed to fabricate the FG Cu foams. X-ray computed tomography observations revealed that the porosity markedly changed around the boundary between the layers of the FG Cu foam with NaCl volume fractions of V f = 80% (high porosity) and V f = 60% (low porosity), and the two layers exhibited almost constant porosities and were bonded seamlessly. From compression tests on the fabricated FG Cu foams, it was found that the V f = 80% layer first deformed while the V f = 60% layer hardly deformed at the beginning of the compression. Thereafter, the V f = 60% layer started to deform. From the compression stress–strain curves, the FG Cu foams exhibited two plateau regions with low and high plateau stresses corresponding to the deformation behavior. The first plateau stress and second plateau stress obtained from the FG Cu foams exhibited similar values to those obtained from uniform Cu foams with V f = 80% and V f = 60%, respectively. Moreover, Cu foams consisting of simply stacked uniform Cu foams with V f = 80% and V f = 60% without bonding exhibited almost the same deformation behavior and compression properties except for slightly larger dispersion than that in the FG Cu foams, which is considered to be due to the lack of bonding and the discontinuity between the pores at the boundary between the V f = 80% and V f = 60% layers.

Relationship between clamp force and pull-out strength in lag screw timber joints

This study empirically examines the relationship between clamp force and pull-out strength in lag screw joints of timber members, using data obtained in tightening tests and pull-out tests. Maximum clamp force per unit screw length as determined from the tightening tests was lower than the lower bound for the 95% tolerance range for pull-out strength per unit screw length as determined from the pull-out tests. Moreover, X-ray CT (computed tomography) observations of anchor members from both tests revealed that failure behavior clearly differed between the tightening test and the pull-out test: tightening caused damage to the wooden, female thread in addition to major splitting damage in the wood perpendicular to the grain near the tip of the lag screw.

Drop Weight Impact Behavior of Al-Si-Cu Alloy Foam-Filled Thin-Walled Steel Pipe Fabricated by Friction Stir Back Extrusion

In this study, Al-Si-Cu alloy ADC12 foam-filled thin-walled stainless steel pipes, which exhibit metal bonding between the ADC12 foam and steel pipe, were fabricated by friction stir back extrusion. Drop weight impact tests were conducted to investigate the deformation behavior and mechanical properties of the foam-filled pipes during dynamic compression tests, which were compared with the results of static compression tests. From x-ray computed tomography observation, it was confirmed that the fabricated foam-filled pipes had almost uniform porosity and pore size distributions. It was found that no scattering of the fragments of collapsed ADC12 foam occurred for the foam-filled pipes owing to the existence of the pipe surrounding the ADC12 foam. Preventing the scattering of the ADC12 foam decreases the drop in stress during dynamic compression tests and therefore improves the energy absorption properties of the foam.

X-ray computed tomography to decipher the genetic architecture of tree branching traits: oak as a case study

A new method for obtaining internal views of tree trunks was recently developed using X-ray computed tomography (CT). This technology makes it possible to observe and measure rameal traces that are left by latent buds, sequential branches, and epicormic branches in the wood. Epicormic branches are undesirable for producing high-value solid wood, especially in Quercus robur, an important hardwood forest tree species in Europe, which is prone to epicormic branches that develop from abundant latent buds. For the very first time, branching-related traits deduced from X-ray CT observation make it possible to analyze the genetic architecture of oak branching through a quantitative trait locus (QTL) analysis. Highly significant QTLs were detected for traits related to latent buds and epicormic branches. The number and effect of these QTLs suggest a moderate genetic determinism for the formation of latent buds and the development of epicormic branches. Three hotspots were found, grouping QTLs for different branching traits. An analysis of the common physiological denominators of these coincident traits suggests that their genetic controls are related to either the regulation of the axillary meristem initiation or to bud dormancy. Conversely, the position of only the separate QTL related to the number of sequential branches suggests an independent genetic control.

Functionally Graded Aluminum Foam Fabricated by Friction Powder Sintering Process with Traversing Tool

Functionally graded aluminum foam (FG Al foam) is a new class of Al foam in which the pore structure varies over the foam, resulting in corresponding variations in the mechanical properties of the foam. In this study, FG Al foam plates were fabricated by a friction powder sintering (FPS) process with a traversing tool that is based on a previously developed sintering and dissolution process. The variation of the mechanical properties was realized by setting the volume fraction φ of NaCl in the mixture to 60, 70, and 80%. Long FG Al foam plates were fabricated with a length equal to the tool traversing length with φ varying in the tool traversing direction. From x-ray computed tomography observation, it was shown that the density of the Al foam decreased with increasing φ. In contrast, almost uniform pore structures were obtained in each area. According to the results of compression tests on each area, the plateau stress and energy absorption tended to decrease with increasing φ. Therefore, it was shown that FG Al foam plates with varying mechanical properties can be fabricated by the FPS process with the traversing tool.

Irregular calcareous sheets preserved in a conch of the Cretaceous ammonoid Hypophylloceras from Hokkaido, Japan

The mantle tissue is essential for understanding the diverse ecology and shell morphology of ammonoid cephalopods. Here, we report on irregular calcareous sheets in a well-preserved shell of a Late Cretaceous phylloceratid ammonoid Hypophylloceras subramosum from Hokkaido, Japan, and their significance for repairing the conch through the mantle inside the body chamber. The sheets are composed of nacreous layers arranged parallel to the irregularly distorted outer whorl surface. The nacreous sheets formed earlier are unevenly distributed and attached to the outer shell wall locally, whereas the last formed sheet covers a wide area of the outer shell wall. The absence of any interruption of ribbing around the irregular area suggests that these sheets were secreted inside the body chamber from the inner mantle. Gross morphological and X-ray computed tomography observations revealed that the spacing of septal formation was not affected by this event. The complex structure of the irregular sheets suggests a highly flexible mantle inside the body chamber.