Publikace & Výsledky

ASEP seznam publikací a výsledků
Scopus seznam publikací

Nejnovější výsledky

Kumpova, I., Vopalensky, M., Fila, T., Kytyr, D., Vavrik, D., Pichotka, M., Jakubek, J., Kersner, Z., Klon, J., Seitl, S., Sobek, J. (2018) On-the-Fly Fast X-Ray Tomography Using a CdTe Pixelated Detector - Application in Mechanical Testing. IEEE Transactions on Nuclear Science, 65(12), art. no. 8482343, pp. 2870-2876. DOI:10.1109/TNS.2018.2873830
Fast tomography measurements are still done almost exclusively within the domain of synchrotrons. However, recent progress in radio diagnostic instrumentation has enabled researchers to perform time-lapse computed tomography (4-D CT) even under laboratory conditions with standard X-ray sources. Thus, fast time-dependent processes within materials with relatively high X-ray attenuation can be monitored. This paper describes the in situ tomographic monitoring of crack formation and propagation in a quasi-brittle silicate matrix composite subjected to three-point bending. A 3-D CT volume containing the region of interest in the specimen is imaged over a period of time, while the continuously increasing load causes crack initiation and propagation, creating a dynamic volume data set. An acquisition time of 50 s for one full-angle tomography with 400 projections makes this tomographic system one of the fastest systems in the world. The resulting visualizations provide qualitative information concerning progressive crack propagation within areas of lower material density. Differential images then allow displaying the spatial orientation of the crack over time.

Ferrucci, M., Hermanek, P., Ametova, E., Sbettega, E., Vopalensky, M., Kumpova, I., Vavrik, D., Carmignato, S., Craeghs, T., Dewulf, W. (2018) Measurement of the X-ray computed tomography instrument geometry by minimization of reprojection errors - Implementation on experimental data. Precision Engineering, 54, pp. 107-117. DOI:10.1016/j.precisioneng.2018.05.007
A procedure for measuring the geometry of X-ray computed tomography (CT) instruments is applied to an experimental CT instrument. In this study, the geometrical measurement procedure is implemented with the CT2 reference object, comprising steel spheres with known center positions in a local coordinate frame affixed to a cylindrical carbon fiber framework. The procedure can be implemented with other sphere-based reference objects, provided the sphere center coordinates are known. The effects of number of acquired projections and rotation mode (stepped or continuous) on the quality of measured geometrical parameters are studied. Finally, the output of the geometrical measurement procedure is used to inform the physical adjustment of the experimental CT instrument to its ideal alignment. The effectiveness of the measurement procedure to correctly determine the instrument geometry is demonstrated from dimensional measurements performed on a tomographically reconstructed validation object from radiographs acquired under initial (misaligned) and adjusted (aligned) instrument geometry.

Top 5 výsledků
Fila, T., Sleichrt, J., Kytyr, D., Kumpova, I., Vopalensky, M., Zlamal, P., Rada, V., Vavrik, D., Koudelka, P., Senck, S. (2018) Deformation analysis of the spongious sample in simulated physiological conditions based on in-situ compression, 4D computed tomography and fast readout detector. Journal of Instrumentation, 13(11), art. no. C11021, DOI:10.1088/1748-0221/13/11/C11021
In this work, an in-house designed table top loading device equipped with a bioreactor is used for the in-situ compression of a spongious sample in simulated physiological conditions. On-the-fly 4D computed tomography is used as a tool for the advanced volumetric analysis of the deforming microstructure of the specimen. The loading device with the bioreactor was placed directly onto the rotational stage of a modular X-ray scanner. As the loading device is equipped with a slip-ring cable system, it can perform an unlimited number of revolutions during the on-the-fly scanning procedure. A complementary metal-oxide-semiconductor flat panel detector with a fast readout was used for the acquisition of the X-ray images. The specimen was compressed with a low loading velocity. A set of the volumetric data capturing the deformation of the specimen during the experiment was prepared from the images acquired by the detector. A digital volume correlation algorithm was used for the evaluation of the volumetric strain fields in the specimen.

Kytyr, D., Zlamal, P., Koudelka, P., Fila, T., Krcmarova, N., Kumpova, I., Vavrik, D., Gantar, A., Novak, S. (2017) Deformation analysis of gellan-gum based bone scaffold using on-the-fly tomography. Materials and Design, 134, pp. 400-417. DOI:10.1016/j.matdes.2017.08.036
Porous hydrogel-based structures reinforced by bioactive nano-particles allows one to design scaffolds with controlled stiffness, strength, and permeability for bone-tissue engineering applications. To be able to reliably assess the mechanical properties, it is necessary to study the material's deformation response on a volumetric basis and in high detail. In this paper, we present an investigation on the compressive characteristics of highly-relaxing gellan-gum bioactive-glass scaffold subjected to continuous uniaxial quasi-static compression. The sample was compressed with a loading rate of 0.4 μm⋅s−1 and simultaneously irradiated by X-rays during several micro-tomographical scans to obtain data for the evaluation of the deformation and strain fields using digital volume correlation (DVC). Such DVC evaluated on-the-fly micro-tomography was very challenging due to the low thickness of cell-walls and the material's intrinsic low attenuation of X-rays. Thus, we employed loading and tomographical devices equipped with a single-photon counting detector coupled with a DVC procedure, all developed in-house. From the acquired 34 tomographical scans, high-resolution voxel models with a resolution of 29.77 μm were developed and subjected to DVC to obtain detailed deformation and strain fields of the material. It is shown that the presented method is suitable for the precise determination of the deformation response of the predominantly organic material developed as a biocompatible, bioresorbable bone scaffold.

Kumpova, I., Vavrik, D., Fila, T., Koudelka, P., Jandejsek, I., Jakubek, J., Kytyr, D., Zlamal, P., Vopalensky, M., Gantar, A. (2016) High resolution micro-CT of low attenuating organic materials using large area photon-counting detector. Journal of Instrumentation, 11(2), art. no. C02003, DOI: 10.1088/1748-0221/11/02/C02003
To overcome certain limitations of contemporary materials used for bone tissue engineering, such as inflammatory response after implantation, a whole new class of materials based on polysaccharide compounds is being developed. Here, nanoparticulate bioactive glass reinforced gelan-gum (GG-BAG) has recently been proposed for the production of bone scaffolds. This material offers promising biocompatibility properties, including bioactivity and biodegradability, with the possibility of producing scaffolds with directly controlled microgeometry. However, to utilize such a scaffold with application-optimized properties, large sets of complex numerical simulations using the real microgeometry of the material have to be carried out during the development process. Because the GG-BAG is a material with intrinsically very low attenuation to X-rays, its radiographical imaging, including tomographical scanning and reconstructions, with resolution required by numerical simulations might be a very challenging task. In this paper, we present a study on X-ray imaging of GG-BAG samples. High-resolution volumetric images of investigated specimens were generated on the basis of micro-CT measurements using a large area flat-panel detector and a large area photon-counting detector. The photon-counting detector was composed of a 10× 10 matrix of Timepix edgeless silicon pixelated detectors with tiling based on overlaying rows (i.e. assembled so that no gap is present between individual rows of detectors). We compare the results from both detectors with the scanning electron microscopy on selected slices in transversal plane. It has been shown that the photon counting detector can provide approx. 3× better resolution of the details in low-attenuating materials than the integrating flat panel detectors. We demonstrate that employment of a large area photon counting detector is a good choice for imaging of low attenuating materials with the resolution sufficient for numerical simulations.

Fila, T., Kumpova, I., Koudelka, P., Zlamal, P., Vavrik, D., Jirousek, O., Jung, A. (2016) Dual-energy X-ray micro-CT imaging of hybrid Ni/Al open-cell foam. Journal of Instrumentation, 11(1), art. no. C01005 DOI:10.1088/1748-0221/11/01/C01005
In this paper, we employ dual-energy X-ray microfocus tomography (DECT) measurement to develop high-resolution finite element (FE) models that can be used for the numerical assessment of the deformation behaviour of hybrid Ni/Al foam subjected to both quasi-static and dynamic compressive loading. Cubic samples of hybrid Ni/Al open-cell foam with an edge length of 15 mm were investigated by the DECT measurement. The material was prepared using AlSi7Mg0.3 aluminium foam with a mean pore size of 0.85 mm, coated with nanocrystalline nickel (crystallite size of approx. 50 nm) to form a surface layer with a theoretical thickness of 0.075 mm. CT imaging was carried out using state-of-the-art DSCT/DECT X-ray scanner developed at Centre of Excellence Telč. The device consists of a modular orthogonal assembly of two tube-detector imaging pairs, with an independent geometry setting and shared rotational stage mounted on a complex 16-axis CNC positioning system to enable unprecedented measurement variability for highly-detailed tomographical measurements. A sample of the metal foam was simultaneously irradiated using an XWT-240-SE reflection type X-ray tube and an XWT-160-TCHR transmission type X-ray tube. An enhanced dual-source sampling strategy was used for data acquisition. X-ray images were taken using XRD1622 large area GOS scintillator flat panel detectors with an active area of 410 x 410 mm and resolution 2048 x 2048 pixels. Tomographic scanning was performed in 1,200 projections with a 0.3 degree angular step to improve the accuracy of the generated models due to the very complex microstructure and high attenuation of the investigated material. Reconstructed data was processed using a dual-energy algorithm, and was used for the development of a 3D model and voxel model of the foam. The selected parameters of the models were compared with nominal parameters of the actual foam and showed good correlation.

Kumpova, I., Fila, T., Vavrik, D., Kersner, Z. (2015) X-ray dynamic observation of the evolution of the fracture process zone in a quasi-brittle specimen. Journal of Instrumentation, 10(8), art. no. C08004, DOI:10.1088/1748-0221/10/08/C08004
The aim of this work is the evaluation of the fracture process zone while loading a quasi-brittle concrete compound. The regularly used optical observation of the specimen surface does not provide accurate information regarding the fracture zone shape, particularly when this zone is tunnelled inside of the specimen body. Therefore, X-ray dynamic defectoscopy and computed tomography were employed as tools for an extended investigation of process zone evolution. A notched specimen manufactured from silicate composite was subjected to the three-point bending test in a special table-top loading device. On-line radiographic observation of the process zone during the loading experiment serves for overall evaluation, while a tomographic measurement - which is conducted during temporal loading interruption - provides information about the spatial distribution of the newly developed cracks.