National Repository of Grey Literature 39 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Fast continuous in-situ XCT of additively manufactured carbon fiber reinforced tensile test specimens
Glinz, J. ; Maurer, J. ; Holzleitner, M. ; Pace, F. ; Stamopoulos, A. ; Vopálenský, Michal ; Kumpová, Ivana ; Eckl, M. ; Kastner, J. ; Senck, S.
The reinforcement of fused filament fabricated (FFF) components with continuous fibers allows for high versatility in the design of mechanical properties for a specific application’s needs. However, the bonding quality between continuous fibers and the FFF matrix material has high impact on the overall performance of the composite. In a recent study [1], additively manufactured (AM) continuous fiber reinforced tensile test specimens have been investigated regarding the effect of amount and material of the embedded continuous fibers on tensile strength and AM build quality. During these tensile tests, a sudden reduction in tensile stress, which most likely was not related to actual rupture of continuous fibers, was noticeable. Since X-ray computed tomography (XCT) scans were performed only prior to and after the tensile testing, a detailed investigation on the origin of these drops in tensile stress was not possible. Within this work, we will expand upon these findings and present results of fast on-the-fly in-situ investigations performed on continuous carbon fiber reinforced specimens of the same AM build. During these investigations, specimens are loaded under the same conditions while fast XCT scans, with a total scan time of 12 seconds each, were performed consecutively. The resulting three-dimensional image data reveals internal meso- and macro-structural changes over time/strain to find the cause of the aforementioned reduction in tensile stress.
Analysis of displacement measured during the compressive testing of cylindrical specimens
Frantík, P. ; Lisztwan, D. ; Kumpová, Ivana ; Daněk, P. ; Rovnaníková, P. ; Keršner, Z.
The paper deals with selected aspects of the analysis of the displacement and deformation stiffness of cylindrical specimens during compressive tests. A developed correction model is presented, and two types of material were selected for the adjustment of the correction model: concrete from an existing structure, and alkali-activated aluminosilicate composite. The correction model was calibrated using the test response of a steel cylinder.
Tomographic investigation of the sandstone fracture toughness
Vavřík, Daniel ; Beneš, Pavel ; Fíla, Tomáš ; Koudelka_ml., Petr ; Kumpová, Ivana ; Vavro, Martin
It is well known that the measured values of the fracture toughness of quasi brittle materials are influenced by material heterogeneity, dimensions, boundary conditions, and unequal tension and compression properties. Standard testing methods supposing isotropic material, in contrary the quasi-brittle materials differ from this theoretical expectation, therefore this approach may fail. The authors present Local Fracture Toughness Testing (LFTT) method to overcome this obstacle. LFFT based on a complex methodology using a series of tomographic reconstructions recorded during specimen loading is calculated independently of the outside boundary conditions.
High resolution region of interest X-Ray tomography
Kumpová, Ivana ; Vopálenský, Michal
The method of X-ray micro-tomography is increasingly used in the research of material characteristics and fracture behavior of building materials. It brings promising results in the field of three-dimensional observation and quantification of microstructure elements, including fracture objects. However, with the standard approach to the tomographic data acquisition, the achievable resolution is severely limited by the size of the examined object resulting in a reduction or even complete loss of useful information regarding, for example, the shape and size of the fracture process zone. For this reason, the possibilities of tomographic targetting of the region of interest with a higher achievable resolution than the usual limit of the tomographic systems have been tested in this work.
Scientific report. Tomography of an archaeological finding – a container with coins
Vopálenský, Michal ; Kumpová, Ivana
The aim of the research is to visualize an archaeological finding of coins (mostly Ag/Cu alloy) in a ceramic container by means of the computed tomography. The artifact is dated to the first half of the 15th century, the visible coins are Prague Groschen and Vienna Pfennigs. The tomographical model should in an ideal case enable to identify the number and type of the coins and other possible materials. Besides of coins, the finding can contain wood, other organic materials (leather) and soil. The container is approx. 20 cm high, with the maximum diameter of approx. 15 cm. The weight of the artifact is 3.8 kg.
Scientific report. Tomography of natural gold findings
Vopálenský, Michal ; Kumpová, Ivana
The aim of the research was to visualize the distribution of gold in natural findings by means of the computed tomography (CT). Gold is present as an alloy with silver (gold being prevalent at least close to the surface, where X-ray fluorescence is applicable). The findings are not homogenous nugets, but stones where gold is distributed in the parent rock (quartz). The purpose of the CT is to visualize the structure of gold in quartz, localize cavities and other structural features.
Analysis of the porosity of a plaster cast, based on tomography data. Pilot measurement for the feasibility verification of the method for analyses of cast sculptures
Kumpová, Ivana ; Vopálenský, Michal
The aim of the tomographical research was the verification of the feasibility of the X-ray tomography for the qualitative description of the internal structure of the cast sculptures (damage, former restoration evidence etc.) and also for the characterization of the way and direction of the plaster pouring. There is a hypothesis that in the cast piece, the non-uniform distribution of pores as for the size (volume) along the vertical direction should be observable. The deeper in the piece, the higher amount of smaller pores and lower amount of bigger pores is expected. As well, lower porosity, i.e., ratio of the volume of the pores and the entire investigated volume, is expected deeper in the sample. The distribution of the pores could indicate, how the sculpture was made, in particular, where were the pouring holes and how many, what was the material flux like and how did it mixture. The method was verified on a specimen and the indicated hypotheses were only partly confirmed.
Region of interest tomography
Vopálenský, Michal ; Kumpová, Ivana
During standard tomographic process, the acquisition of tomographic data (projections) is performed with geometric adjustment of the tomographic assembly ensuring that the projection of the entire width of the examined object fits onto the detector during the full object rotation. Because of the limited width of the detector, this approach has a limited maximum achievable resolution for the given specimen diameter. It is possible to make higher magnification, but then the projections do not fit onto the detector, which causes certain problems during the reconstruction, but allows achieving of higher resolution in the always-visible region of the object (the region of interest). The research was focused on evaluation of ROI tomography approach on the TORATOM tomograph.
Tomography of a bronze axe of the Únětice culture, found in Kukleny, Hradec Králové
Kumpová, Ivana ; Vopálenský, Michal
It has been shown in the past that the computed X-ray tomography can bear significant new findings on the distribution of damaging and other structural details of the bronze findings. However, relatively high beam energies are necessary and it is not a priori ensured that the object under test would be penetrated with the radiation sufficiently. A big problem is also the photon scattering, which can make fine details indistinguishable. Therefore, a chosen Únětice culture axe has been submitted to a tomographical investigation in the laboratory of X-ray tomography of the Institute of Theoretical and Applied Mechanics of the Czech Academy of Sciences, v.v.i. The result should confirm the suitability of the method for investigations of other similar bronze findings.
Scientific report. Sps_025: Ceramics B4C + 1Ti, 1800°C, 2 min
Kumpová, Ivana ; Vopálenský, Michal
The aim of the measurement was to verify the feasibility of 3D computed tomography for observing structural details in samples of B4C - Ti ceramics with 1 % of Ti. Sample designated Sps_025: Keramika B4C + 1Ti, 1800°C, 2 min, in the form a cylinder with the diameter of 12 mm and the height of 10 mm was investigated by this method.

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22 KUMPOVÁ, Ivana
22 Kumpová, Ivana
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