Papers by Keyword: X-Ray Tomography

Abstract: Our current study concerns the structural analysis and mechanical properties under compressive loading of a new developed additive-manufactured hydroxyapatite (HA) scaffolds, designed for bone tissue engineering. Structural evaluation was performed by X-ray computed tomography (X-CT) and the compressive strength was determined by uniaxial testing method to compare the performance of the new structured material with those reported in the literature. The studied scaffolds showed a well-defined periodic structure with a well-controlled interconnected porosity which is about 32 %. The compressive strength was of 60 MPa and the Weibull modulus of 6. These values are higher than those generally obtained on porous scaffolds fabricated by other techniques with the same level of total porosity. These results demonstrate the potential use of this 3D printed scaffolds for load bearing bone tissue.

Abstract: This study utilized the Philippine burley and native tobacco as reinforcing materials to Polylactic Acid (PLA) in creating novel natural fiber-thermoplastic 3D printing filaments. As a new material for 3D printing, the effects of fiber loading, fiber species, and printing pattern on the mechanical properties of the tobacco fiber-PLA composites were investigated. Regardless of tobacco species and fiber loading, the honeycomb pattern showed superior tensile strength than its rectilinear counterpart. The same trend was also observed in the impact strength of some tobacco-PLA samples. Increase in fiber loading on the other hand, decreased the flexural strength and flexural modulus of the tobacco fiber-PLA composites. The trends in the mechanical properties were then analyzed using 3D X-Ray Computed Tomography, which allowed analysis and visualization of voids and layer patterns.

Abstract: It is assumed, that the pore content is related to other parameters of CIPP liners such as mechanical properties and service life or durability of pipelines. The article examines the pore structure of two different materials - composites pipes cured with steam and UV light. The pore structure was examined using an optical microscope and X-ray computed tomography (CT). The aim of the work was to verify the applicability of some methods for verifying the volume of air/gas in the cured composite.

Abstract: In the present work, the self-healing process in concrete was evaluated using analytical techniques. For this purpose, two concrete mixes of different composition (one used as control) were prepared with a water-to-binder ratio of 0.45. The self-healing process was triggered by the introduction in the concrete mix of a commercial expansive admixture (calcium sulfo-aluminate), two dicarboxylic acids, and sodium carbonate salt. After 28 days curing in water, the specimens were artificially cracked (crack width ≤ 900 μm) and then again water-cured for further 60 days until self-healing occurred. The progress of self-healing was investigated with a stereomicroscope at 40, 50, and 60 days, after cracking, to identify the quality and the degree of the healing. The efficiency of the self-healing process was also evaluated using micro-Raman spectroscopy and X-ray micro-computed tomography. Significant reduction in the crack width was observed as a result of a calcite filling, generated during the self-healing process. In some cases (crack width < 400 μm), the crack was completely healed. The experimental methodology used provided new insights into the evolution of the self-healing phenomenon in concrete.

Abstract: Portland-limestone cement paste specimens were stored in magnesium sulfate solution at 5°C for 6 months; the occurring microstructural changes have been monitored on a monthly basis. Extent of deterioration was quantitatively assessed with different techniques. The X-ray micro-computed tomography was employed to describe non-invasively the pore structure and extend of deterioration. X-ray powder diffraction and infrared spectroscopy were used to characterize the phase changes occurred in the course of the sulfate attack. Compressive strength tests reflected the effect of the process on mechanical performance. The results indicate the rapid degradation of the system, owing, mainly, to crack formation, expansion, and finally loss of cohesion between the deteriorated parts of the specimens and the sound cement matrix, as a consequence of the formation of new phases. The progress of an irregular deterioration front was observed. The presence of complex phases (thaumasite, ettringite) was proved, however, the deteriorated parts of the specimens mostly consisted of gypsum.

Abstract: Recent experiments resolved nucleation and growth of graphite during solidification of ductile cast iron in 4D using synchrotron X-ray tomography. A numerical model for microstructure formation during solidification is compared with the experiments. Despite very good overall agreement between observations of spheroidal graphite growth and model results, significant deviations exist towards the end of solidification. We use the experimental observations to analyse the relation between graphite growth rate and the state of the particle neighbourhood to pinpoint possible links between growth rate of individual graphite spheres and the overall solidification state. With this insight we revisit existing models for growth of spheroidal graphite and discuss possible modifications in order to correctly describe the critical final stage of solidification.

Abstract: The invention of computed tomography some few decades ago, coupled with its applications in the field of non-destructive testing for industrial objects inspection has revolutionized the way inspections were formerly done. Despite the conventional data acquisition scheme which is integrated with a rotational stage in between the source and the detector works perfectly for small and lighter objects, hence, it seems impossible to investigate complicated, bulky objects with interconnected unbalanced composites. Moreover, it will be very expensive to harnessed technologies into the rotational stage which can be incorporated into this conventional technique with an optimum degree of accuracy. Therefore, this paper will consider the translational data acquisition scheme which is proven mathematically as an alternative method to the conventional technique [1]. This translational scheme takes into account the variations and the magnification of both the source x-ray and the detector around the object and then proceeded by scans from different focal distances. Python packages with necessary plugins were used in implementing the reconstructive algorithm generated in simulating and modelling a suitable image of inspected object.

Abstract: The problem of formation of a material, which has the coefficients of attenuation and scattering close or coinciding with the same coefficients for some other predetermined material, was considered. A computer processing of values of these coefficients for a big set of various materials has been carried out and their dependence on radiation energy value was studied. The conclusion was drawn about probability of successful solution of the problem in some cases and difficulties, which may occur were pointed out. A set of computer calculations carried out for some specific materials is provided.

Abstract: The crack initiation and propagation during bending have been considered to be affected by second phase particles, micro-voids and shear-bands. However, the effects of the second phase particles and the micro-voids on the crack initiation and propagation during bending have not been fully investigation. In this study, the effect of the second phase particle distribution on the formation of micro-voids, and the effect of the micro-voids on the crack initiation and propagation during bending were investigated using the largest synchrotron radiation facility “SPring-8” and FE-SEM/EBSD. With the bending ratio increasing, the micro-voids increased around the coarse particles near the outer surface. In particular, coarse micro-voids were formed around coarse particles with a high aspect ratio on the shear-bands. At a large cracked part, coarse micro-void was observed at the outmost layer section as a crack initiation site, and coarse micro-voids and asheared fracture surface were observed at the crack propagation site. At the small cracked part with no propagation, cube orientation grains were located under the small crack. It was considered that these cube orientation grains inhibited the formation of shear-bands, therefore, propagation of the cracks did not occur at the small cracked area.

Abstract: During the pre-forming stage of the RTM process, large deformations can occur, especially for double-curved shapes. Knowing the mechanical behaviour and the actual geometry of fibrous reinforcements at the mesoscopic scale is of great importance for several applications like permeability evaluations. As such, forming modeling is particularly demanding on the quality of geometric modeling and of the mesh associated. Indeed, analysis of the internal structure of materials in general, and woven materials especially, recently led to major advances. X-ray Micro Tomography (XRMT or μCT) allows detailed and accurate 3D observations inside the sample, which is not possible with the standard microscopy techniques restrained to surface observations. It distinguishes the yarns and even the fibers that define the directions of anisotropy of the material. A FE model is generated from the processed tomography images. It has been chosen in this study to use hypoelasticity behaviour law. Indeed, the yarns are submitted to large deformations, so that the orientation of the material is significantly modified and the fiber direction has to be strictly followed in order to fulfil the principle of objectivity. A way to retrieve the neutral composite reinforcement axis by skeletonization is proposed in order to know the privileged direction of the yarn and thus implement it in the constitutive law. A comparison between experimental and simulations obtained from μCT and idealized geometry of a transverse compression test on the G0986 is presented.