X-ray CT Method Research Articles

異方性Gursonの降伏関数を用いた発泡金属材料の弾塑性変形解析

It is important to formulate a constitutive equation which represents the growth of voids during plastic deformation in order to predict ductile fracture of metallic materials. For this purpose, we proposed an anisotropic Gurson’s yield function with the damage tensor, which represents the anisotropy due to the void distribution. In this study the void distribution of porous metal ADC12 was obtained 3-dimensionally using X-ray CT method and the corresponding damage distribution was also calculated from the obtained void distribution in terms of voronoi tessellation method. Then we carried out the finite element analysis for the uniaxial tensile test of porous metal using both the anisotropic Gurson and von Mises type constitutive equations and compared the calculated results of the anisotropic Gurson model to those of usual von Mises model. It was seen that the plastic strain concentrated area of the anisotropic Gurson model is corresponds to those of von Mises model.

X-ray computed microtomography and 2D image analysis for morphological characterization of short lignocellulosic fibers raw materials: A benchmark survey

Optimizing the performance of lignocellulosic fibers often requires relating mechanical behavior or morphological characteristics to microstructure. X-ray computed microtomography (X-ray CT), which provides 3D images with a high level of detail at both the micro- and macro-scales, may overcome these difficulties. This work provides a comparative analysis of the potential of X-ray CT (3D) and an office scanner (2D) for morphological characterization of lignocellulosic fibers. To this end, three specimens of lignocellulosic fiber materials obtained after the first decortication of the plant were retained. X-ray CT and 2D scanning correlations of sample diameter distributions are presented. The general aspects of the fibers diameter correlation are discussed. Image analysis was used to assess the potential and limitations of both the X-ray CT and 2D scanning methods based on the experimental work, and the main conclusions of the benchmark study are given in a table.

Application of X-ray CT method for discontinuity and porosity detection in 316L stainless steel parts produced with SLM technology

Industrial tomography (XCT) is a nondestructive test method that provides information about spatial distribution of X-ray absorption in the analyzed structures. The aim of this paper was to examine the possibility and accuracy of application of XCT method for discontinuity and porosity detection in parts made of 316L stainless steel powder produced by Selective Laser Melting technology. Analysis conducted on three produced test samples showed that the application of XCT as a method of quality control of specimens produced with an additive manufacturing technology offers a wide range of possibilities to detect porosity within materials. Parameters such as the amount of porosity, pore size and pore shape are presented. Accuracy of XCT method strongly depends on the size of the samples analyzed, but the possibility of obtaining information in 3D nondestructively shows considerable advantages of XCT method over traditional metallographic cross-sectional analysis.

Combining electrical resistance and 3-D X-ray computed tomography for moisture distribution measurements in wood products exposed in dynamic moisture conditions

Strength and durability of wood-based products are substantially influenced by moisture. It is, therefore, crucial to monitor the moisture content (MC) distribution in wood products to fully understand their behaviour in dynamic moisture conditions. In this paper, we present a combined X-ray CT method and an adapted version of the electrical resistance MC measurement method for detailed studies on MC distribution in wood products. The X-ray CT method is evaluated using the gravimetrically recorded MC of solid wood. Subsequently, the recorded MC of electrical method is evaluated by using X-ray CT method. Three wood products are used for this purpose, i.e. solid wood, plywood and oriented strand board (OSB) panels. It is proven that X-ray CT method can accurately determine the MC of wood products and thus has great potential for non-destructively measuring the MC distribution in 3D. Furthermore, the results show that electrical method can effectively record the local MC when the MC distribution in this region is even. Otherwise, the position of the electrodes, with regard to specific wood properties has a substantial influence on its performance. Compared with solid wood and OSB, the electrical method performs best in plywood due to its layered structure. The adapted electrical method is an effective tool for continuously monitoring the MC distribution of wood products, taking into account that the electrodes are installed correctly according to the structure of the material and research questions. Combined with X-ray CT scanning, MC distribution of wood-based products under in-service applications, can be monitored.

Analysis of the Tracer Diffusion Phenomena through Cracks in the Porous Media by Means of X-Ray CT

The migration process of contamination materials in the porous rock mass was visualized and analyzed by X-ray CT image data. In this study, Kimachi sandstone, which had approximately 26% porosity, was used as a rock sample. Here two cases of diffusion phenomena were analyzed. One is the case that solute diffuses into the porous rock mass from the crack surfaces, and it simulates the contamination process of rock mass. Another is the case that the solute diffuses out of the porous rock mass, and it simulates the process that the contamination materials spread from highly contaminated sources. It was found that the diffusion phenomena were clearly visualized by X-ray CT method. By introducing the parameter, coefficient of tracer density increment α, quantitative analysis of tracer density became possible, and the relation between the density distribution of tracer and the crack apertures and the relation between the density distribution and porosity distribution became clear.

Tillage effects on topsoil structural quality assessed using X-ray CT, soil cores and visual soil evaluation

Soil structure plays a key role in the ability of soil to fulfil essential functions and services in relation to, e.g., root growth, gas and water transport and organic matter turnover. The objective of this paper was: (1) To quantify tillage effects on soil structural quality in the entire topsoil layer (0–20cm) using X-ray CT, visual evaluation and traditional core methods; and (2) To correlate pore network characteristics from X-ray CT imaging with the results from the visual evaluation and the core method. Samples were taken in May 2009 from a long-term rotation and tillage field experiment on a Danish sandy loam. The tillage treatments were direct drilling (D) and ploughing (P). For X-ray CT scanning, we sampled large soil cores (Ø=20cm, height=20cm) from the top layer. Small 100cm3 samples were taken from the 4–8 and 12–16cm layers for water content and bulk density measurements. Visual soil structure evaluation was carried out in the field at the same time as sampling. CT images (0.39×0.39×0.6mm3 voxels) were produced using a medical X-ray CT scanner. The visual assessment showed a good structural quality in the top 5–8cm for both treatments (Sq<2). A poorer soil structure was observed in lower part or the topsoil where a firm structure (Sq=2.9) was observed for D and relatively friable structure (Sq=2.2) for P. Lower bulk density was found for P than for D in the 4–8cm layer (1.34 and 1.52gcm−3, respectively), whereas relatively high bulk density values were observed for both treatments in the 12–16cm layers (1.50 and 1.56gcm−3, respectively). The X-ray CT image analysis showed that the P soil had more networks, branches and junctions but a lower degree of anisotropy and shorter average branch length than the D soil. The image data also confirmed a clear stratification of the 0–20cm topsoil layer for both tillage treatments. The stratification of the direct drilled soil was in accordance with our expectations whereas it was surprising for the ploughed soil. The dense lower topsoil layer for the ploughed soil was probably caused by compaction during secondary tillage and natural consolidation, and aggravated by a poor structural stability due to a low organic matter content. The visual soil evaluation scores were negatively correlated to soil porosity and number of pore networks estimated from X-ray CT imaging and positively correlated to the macropore characteristics of branch length and pore thickness.

Visualization of soil arching on reinforced embankment with rigid pile foundation using X-ray CT

The purpose of this paper is to study and compare arching in reinforced and unreinforced piled embankments for different fill materials and pile spacings. Toyoura sand, silica sand no.7, silica sand no.8 and dry powder clay are used as fill materials. In this study, X-ray CT method is used as a non-destructive technique to examine the load distribution mechanism quantitatively. Vertical cross sectional images are constructed by the data obtained from CT scanning. It is seen that low density areas represent the shear planes and dilatancy in the arch within the piled embankment. The angle of density change is defined as the angle formed by the arch-shaped shear plane and the horizontal plane within the inter-pile soil. While Toyoura sand has the smallest angle of density change due to the largest peak internal friction angle and the effective particle size, dry powder clay has the largest angle of density change. The earth reinforcement is found to be effective with the use of pile elements for the purpose of stress re-distribution in the fill. Furthermore, the amount of the embankment loading is visualized by three dimensional extraction images. The effectiveness of the proposed method is verified by conducting a comparative study with the current Japanese design model. It is shown that, using X-ray CT method and visualization techniques provide a better understanding of soil arching in a reinforced embankment with rigid pile foundation system.

Analysis of Swelling and Homogenization Process of Bentonite by X-ray CT Method

Analysis of Swelling and Homogenization Process of Bentonite by X-ray CT Method

Arching Observation in Three-Dimensional Trapdoor Problem with X-Ray CT and Discrete Element Method

ABSTRACT A comparative study of the trapdoor problem is proposed in this paper involving experimental model tests on one side and a Discrete Element Method modelling on the other side. Most of the past studies related to the arching effect and the trapdoor problem were performed under plane strain or axisymetric conditions. The observation of the arching mechanisms is indeed simplified under these special test conditions. In this paper, the trapdoor problem was simulated under three-dimensional testing conditions with a square-shaped trapdoor. The granular layers were made with monodisperse glass beads. The arching mechanisms were experimentally investigated with X-ray Computed Tomography. Based on the images obtained, the propagation in the granular layer of the disturbance due to the displacement of the trapdoor was monitored. On the other side, the intensity of the load transfers in the granular material was evaluated with a force measurement apparatus on the trapdoor. In parallel, a numerical analysis involving the Discrete Element Method was conducted to predict both the qualitative and the quantitative phenomena. The gradual local expansion of the granular layer due to trapdoor displacement and the load transfer amplitudes were very well reproduced. An agreement between the experimental and the numerical results was obtained for small displacements of the trapdoor (high load transfers) as well as for larger displacements of the trapdoor.

X線CT法による多孔質岩石亀裂内および岩石マトリクスへの移流・拡散現象の分析

The advection in the crack and the diffusion from the crack surface to rock matrix of contaminated materials in a rock mass are one of the important factors to evaluate the characteristics of the rock mass as a natural barrier function for a radioactive waste disposal project.In this study, X-ray CT method was applied to evaluate the advection in the crack and the diffusion of solute from the crack surfaces to the rock matrix. In order to visualize advection and diffusion phenomena, the tracer migration tests have been applied to the porous sandstone and the tracer migration and diffusion process was visualized by X-ray CT scanner. In order to evaluate density distribution in the crack and pores in the rock matrix, advanced coefficient of tracer density increment was defined. In this study, the relations between the flow in the crack and the amount of the diffused tracer into the rock matrix were discussed. The influences of the crack aperture to the tracer diffusion process were also discussed.

Ｘ線ＣＴ法による多孔質岩石内ＣＯ２残留ガストラップ現象の分析

CCS (Carbon dioxide Capture & Storage) is expected as one of most efficient methods in order to reduce the amount of exhausted CO2 into the air. In the projects, the estimation of storage volume and the assessment of CO2 trapping effect in the reservoir are necessary. The objective of this paper is to analyze the residual CO2 trapping in the porous media after the storage of CO2 in the aquifer by means of X-ray CT. The CO2 injection and successive water injection test were conducted, and the replacement and trapping process of water — CO2 was analyzed by X-ray CT method. Here, the amount of CO2 replaced in the pore during CO2 injection tests was estimated. The amount of residual CO2 trapped in the rock pore during successive water injection tests was also estimated, and relations between the replaced/trapped CO2 and the porosity distribution of rock were discussed. It was found that more CO2 was stored at the relatively high porosity region, and that the residual ratio at the high porosity region easily decreased during the water injection process. However, it was also found that the approximately 10 % of injected CO2 was still remained after the six to ten times pore volume of water was injected into the rock sample.

Microfocus X-ray CT method for the reconstruction of fossil internal structure : A case of spiriferid brachidium

Microfocus X-ray CT method for the reconstruction of fossil internal structure : A case of spiriferid brachidium

Ｘ線ＣＴ法による亀裂内トレーサー移行プロセスの可視化と分析

The advection and dispersion of contaminated materials in a rock mass are one of the important factors to evaluate the characteristics of the rock mass as a natural barrier function for a radioactive waste disposal project. In this study, X-ray CT method was applied to evaluate the advection and dispersion of solute in the crack which exists in rock mass. In order to visualize advection and dispersion phenomena, the tracer migration test have been conducted and tracer migration process was visualized by X-ray CT scanner. Here, an indicator, coefficient of tracer density increment, was newly introduced to analyze tracer migration. This is the indicator that represents the density of the tracer in the crack, and the evaluation of the density distribution of the tracer becomes possible. In this study, the influences of the crack aperture to the tracer migration process are discussed.

Application of Local Tomography Technique to High-Resolution Synchrotron X-Ray Imaging

X-ray CT method is a kind of nondestructive inspection, but has strong limitation in sample size due to a small field of view (FOV). The higher the resolution, the smaller FOV is, mainly due to the element number of available detectors commercially. Therefore, sample machining is more or less necessary so that the sample size is fit within the small FOV in the case of the high-resolution observation. Local tomography technique enables a high resolution reconstruction of small region of interests within a sample without the sample machining. In this study, we have evaluated the size effects of aluminum foam samples in terms of the 3D image quality by the local tomography techniques.

４．非線形力学 杭の３次元水平抵抗メカニズムの可視化

The objective of this paper is to visualize 3-D lateral bearing capacity mechanismusing X-ray CT method. Here, the apparatus of model loading test was developed and a series of model loading test were conducted using this apparatus in the system of X-ray CT scanner. First of all, lateral soil cutting test with flat blades in sand was examined for the purpose of fundamental study on the lateral bearing capacity. Then, model pile loading test was conduced with same sandy ground. Cr scanning was done for the model ground during the process of lateral loading. Not only 2-D cross sectional images for the ground but also 3-D ones were obtained from CT scanning and precise failure patterns of the ground in 3-D due to lateral loading was discussed. Finally, the effectiveness of X-ray CT scanner was confirmed based on all the results in this study.

CHARACTERIZATION OF SEEPAGE AND DRYING ON LIGHT WEIGHT SOIL WITH AIR FOAM USING X-RAY CT METHOD

CHARACTERIZATION OF SEEPAGE AND DRYING ON LIGHT WEIGHT SOIL WITH AIR FOAM USING X-RAY CT METHOD

Three-dimensional description of the Kobe meteorite by micro X-ray CT method: Possibility of three-dimensional curation of meteorite samples.

The Kobe meteorite was imaged by a micro X-ray CT scanner to examine the possibility of three-dimensional curation of meteorite samples without destruction. Materials including major minerals in meteorites were also imaged to obtain a quantitative relation between CT value, which is numerical expression of CT contrast, and X-ray linear attenuation coefficient (LAC) of the materials under polychromatic X-ray beams. CT values of the samples are normalized by that of an olivine crystal from San Carlos, U.S.A. (SCO = San Carlos olivine: Fo91.8), which was imaged under the same condition as a standard material (normalized CT value = CT value(sample)/CT value(SCO) × 100 [OU]: OU = olivine unit). The normalized CT values almost equal to similarly normalized LAC values calculated for the samples at <150–250 OU. We can estimate materials by the normalized CT value-LAC relation even if we use polychromatic X-ray beams. Successive 380 CT slice images of apiece of the Kobe meteorite (Kobe C-5-1; 1.144 g and 7–9 mm) were taken to obtain the three-dimensional structure. The pixel size of 31.6 μm × 31.6 μm and the slice width of 25.3 μm determine the spatial resolution for the images of about 60–90 μm. Thin sections were made to compare the CT images with images by an optical microscope, SEM and X-ray fluorescent microscope. In the CT images, we can distinguish plagioclase, ferromagnesian silicates (mainly olivine), magnetite-pentlandite and molybdenite. The CT value for the ferromagnesian silicates is approximately the same as that expected from olivine of FO∼69 in the meteorite. Orthopyroxene and clinopyroxene were not distinguished from olivine due to their small grain sizes and LAC values similar to olivine. Magnetite and pentlandite cannot be distinguished from each other due to their similar LAC values. The CT values of magnetite-pentlandite aggregates are smaller than those expected from their LAC values because the aggregates have inclusions of silicate minerals and Ca phosphates. The CT value of plagioclase is slightly larger than that expected due to small inclusions too. Chondrules with rims with different contrasts can be recognized while chondrules without rims cannot. The two-dimensional shapes of some magnetite-pentlandite aggregates are circular like opaque chondrules under an optical microscope. However, they are not in spherical shape three-dimensionally. Their sub-rounded shapes might be formed by partial melting of these aggregates probably at the same time as a local melting of plagioclase and some olivine. The sample was cut into seven plates for different analysis at different laboratories. Three-dimensional CT images were made for the plates to understand their internal structures. The present results suggest that curation of meteorites is possible by micro X-ray CT.

円錐孔底ひずみ法におけるコアディスキング現象に関する基礎的研究

Core disking is sometimes observed in high stress region where rock stress measurements are performed by the Compact Conical-ended Borehole Overcoring (CCBO) Technique, which is one of the stress relief methods. When the tensile stress induced on the borehole bottom surface becomes larger than the tensile strength of the rock, a failure from the borehole bottom surface will be imitated. Therefore, if the stress changes on the borehole bottom surface can be analyzed during overcoring, the rock stress prior to boring may be estimated.In this paper, assuming that the tensile stress on a borehole bottom surface induced due to overcoring is one of factors of generating core disking, the mechanism of the core disking in the CCBO is discussed as well as the location of failure initiation and the type of failure. Firstly, the characteristics of core disking in the CCBO is shown. Secondly, simulating the overcoring of the CCBO under three dimensional initial stress state in which the axis of a principal stress coincides with that of a borehole, the failure initiated on the borehole bottom surface during the overcoring is discussed, based on the results calculated by a semi-analytical boundary element process for axisymmetric elasticity with arbitrary boundary element conditions. From the results, the criterion of core disking is suggested and the applicable limitation of the CCBO is made clear. Furthermore, the X-ray CT method is applied to the recovered core with core disking, and then the state of failure within the core is visualized. Finally, it is discussed that the rock stress prior to boring is estimated by the suggested criterion of the core disking, comparing the neighboring rock stress measurement and tensile strength obtained from cores.

Application of X-Ray CT Method for Characterization of Failure in Soils

ABSTRACT X-ray computed tomography scanners, better known as “X-ray CT scanners” have been widely used for medical purposes. But recently, this machine has for engineering purposes been developed as a nondestructive method for any kind of material. In this paper, the application of X-ray CT scanners for characterization of failure in soils is examined using undisturbed soil specimens under unconfined compression. This CT scanner was developed for industrial purposes so that the x-ray capacity is much higher than that used in a medical setting. Here, the change of density under the deformation in the soil specimen can be investigated without any destruction. Not only 2-D cross sectional images but also 3-D images of the deformed soil specimen were obtained without any destruction of the specimen and the behavior in the soil not only visualized but also evaluated quantitatively. Thus, the effectiveness of the X-ray CT method for geotechnical engineering was confirmed.

Pictorial 1 : Three-dimensional Structures of Chondrules by X-ray CT Method

Pictorial 1 : Three-dimensional Structures of Chondrules by X-ray CT Method