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Optical evaluation of corrosion products using colorimetric spectroscopy
Majtás, Dušan; Fialová, P.
2019 - anglický
Aim of this work is to test possibility to utilize colorimetric spectroscopy for monitoring the corrosion of lead and tin-lead alloys. And furthermore method suitability for preliminary corrosion evaluation of cultural heritage objects. According to literature colorimetry is used to monitor patinas of bronze objects, thus the method might be also suitable for lead based alloys. Samples used were made from commercially produced lead plate. These were exposed in the climatic chamber to different relative humidity (60, 80, 90 %). After the exposure the corrosion products with different color formed on sample surface. These corrosion products were evaluated by different methods: optical microscopy, colorimetric spectroscopy, and X-ray chemical analysis. Collected colorimetric data display difference between treatments suitable for patina evolution monitoring. The paper presents obtained results and comparison of applied methods.
Klíčová slova:
colorimetry; corrosion; cultural heritage; laboratory simulation; lead; optical method; spectroscopy
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Optical evaluation of corrosion products using colorimetric spectroscopy
Aim of this work is to test possibility to utilize colorimetric spectroscopy for monitoring the corrosion of lead and tin-lead alloys. And furthermore method suitability for preliminary corrosion ...
Stochastic resonance in dynamics and related disciplines
Náprstek, Jiří; Fischer, Cyril
2019 - anglický
Stochastic resonance (SR) is a phenomenon which can be observed in some nonlinear dynamic systems under combined excitation including deterministic harmonic force and random noise. This phenomenon was observed the first in the early 1940s when investigating the Brownian motion. Later several disciplines in optics, plasma physics, biomedicine and social sciences encountered effects of this type. However, the actual discovery and start of intensive period of investigation is dated in early 1980s when the idea of SR initiated remarkable inter disciplinary interest including most areas of physics, chemistry and neuro-physiology with a significant overlap to engineering and industrial area. Promising opportunities to employ SR in mechanics emerged only recently to model certain post-critical effects in non-linear dynamics and simultaneously to develop new vibration damping devices, energy harvesting facilities, sophisticated measuring technics and others. The aim of the paper is to present information about a new challenging discipline offering a large field of basic research and possibilities for practical applications.
Klíčová slova:
stochastic resonance; interwell hopping; non-linear vibration; Fokker-Planck equation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Stochastic resonance in dynamics and related disciplines
Stochastic resonance (SR) is a phenomenon which can be observed in some nonlinear dynamic systems under combined excitation including deterministic harmonic force and random noise. This phenomenon was ...
High strain-rate compressive testing of filling materials for inter-penetrating phase composites
Doktor, T.; Fíla, T.; Zlámal, Petr; Kytýř, Daniel; Jiroušek, O.
2019 - anglický
In this study behavior of the selected types of filling material for the inter-penetrating phase composites was tested in compressive loading mode at low and high strain-rates. Three types of the filling material were tested, (i) ordnance gelatin, (ii) low expansion polyurethane foam, and (iii) polyurethane putty. To evaluate their impact energy absorption bulk samples of the selected materials were tested in compression loading mode at strain-rates 1000 s−1 to 4000 s−1. The high strain-rate compressive loading was provided by Split Hopkinson Pressure Bar (SHPB) which was equipped with PMMA bars to enable testing of cellular materials with low mechanical impedance. Based on the comparative measurement response to compression at both low and high strain-rates was analysed. The results show a significant strain-rate sensitivity of the ordnance gelatin and of the polyurethane putty, while strain-rate effect in the polyurethane foam was not observed.
Klíčová slova:
interpenetration phase composite; SHPB; impact protection filling materials; strain-rate sensitivity
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
High strain-rate compressive testing of filling materials for inter-penetrating phase composites
In this study behavior of the selected types of filling material for the inter-penetrating phase composites was tested in compressive loading mode at low and high strain-rates. Three types of the ...
X-ray micro-tomography characterization of voids caused by three-point bending in selected alkali-activated aluminosilicate composite
Kumpová, Ivana; Rozsypalová, I.; Keršner, Z.; Rovnaníková, P.; Vopálenský, Michal
2019 - anglický
This paper deals with the pilot characterization of a special alkali-activated aluminosilicate composite composed of waste brick powder, brick rubble and a solution of potassium water glass. Fracture tests were conducted on the specimens via three-point bending and fracture parameters were evaluated. Selected specimen was investigated using micro-tomography to supplement the results with visual information about the inner structure of this newly designed material before and after the mechanical loading. Tomographic measurements and image processing were conducted for a qualitative and quantitative assessment of changes in the internal structure with an emphasis on the calculation of porosimetric parameters and visualization of the fracture surface. Fractal dimension of fracture surface was estimated.
Klíčová slova:
alkali-activated aluminosilicate composite; fracture surface; X-ray micro-tomography; 3D porosity evaluation; fractal dimension
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
X-ray micro-tomography characterization of voids caused by three-point bending in selected alkali-activated aluminosilicate composite
This paper deals with the pilot characterization of a special alkali-activated aluminosilicate composite composed of waste brick powder, brick rubble and a solution of potassium water glass. Fracture ...
Evaluation of self-healing in concrete by means of analytical techniques
Aspiotis, K.; Sotiriadis, Konstantinos; Kumpová, Ivana; Mácová, Petra; Badogiannis, E.; Tsivilis, S.
2019 - anglický
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 reference) were prepared with a W/B 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 ≈ 400 μm) and then again water-cured for 40 days until self-healing occurred. The progress of self-healing was investigated with a stereo-microscope at 40, 50 and 60 days. The efficiency of the process was evaluated using micro-Raman spectroscopy and X-ray micro-computed tomography (XmCT). Significant reduction in the crack width was observed as a result of filling the crack with calcite generated during the self-healing process. In some cases, the crack was completely healed. The experimental methodology used provided new insights into the evolution of the self-healing phenomenon in concrete.
Klíčová slova:
self-healing; concrete; chemical additives; Raman spectroscopy; X-ray tomography
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Evaluation of self-healing in concrete by means of analytical techniques
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 reference) were prepared ...
Proposal for loading tests of bridges - simulation and laboratory experiments
Bayer, Jan; Urushadze, Shota; Černý, Miloš
2018 - anglický
A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient solution of piecewise linear mechanical structures were developed to assess the effects of the proposed dynamic load on a bridge model. According to the first laboratory experiments, it seems that the proposed travelling impulse load could surpass some of the shortcomings and limitations of the currently applied methods of bridge testing. The investigation is a part of a project aimed at drive-by identification of dynamic properties of bridges and further experimental and analytical research will follow.
Klíčová slova:
dynamic loading tests; transient analysis; vibrations; vehicle-bridge interaction
Dokument je dostupný na externích webových stránkách.
Proposal for loading tests of bridges - simulation and laboratory experiments
A new dynamic load testing of bridges is proposed and theoretically investigated. A transient analysis of passing vehicle over a bridge in ANSYS and an analytical program in MATLAB for the transient ...
Strength of composite yarn under biaxial loading
Valentová, S.; Hrbek, Vladimír; Vorel, J.; Šejnoha, M.
2018 - anglický
The present paper is concerned with two types of periodic unit cell of composite yarn with different geometry but the same material properties. Their macroscopic response under tensile and compressive loading in the transverse direction and their combination are plotted in the graphs. Based on stress-strain curves the failure envelopes are constructed. A simple maximum stress criterion and linear softening law is used in the adopted progressive damage analysis to outline the softening part of stress-strain diagrams. Finally the impact of selected representative volume element is observed through the comparison of results gained for both designed periodic unit cells in the microlevel, meaning the level of yarn.
Klíčová slova:
composite yarn; periodic unit cell; strength; damage analysis; failure envelope
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Strength of composite yarn under biaxial loading
The present paper is concerned with two types of periodic unit cell of composite yarn with different geometry but the same material properties. Their macroscopic response under tensile and compressive ...
Asymmetry of the response probability density of a system with parametric random noises
Náprstek, Jiří; Fischer, Cyril
2018 - anglický
Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These parasitic processes are usually of the random character and, consequently, they exercise as parametric noises. Moreover, the input signal mostly consists of a useful signal which can be taken as composed from deterministic and random additive part. Various combinations of these noises are the origin of random and also systematic measuring errors which can have under certain circumstances a cumulative character, deteriorate the output signal quality and can lead finally to the stochastic stability loss. These effects can be theoretically described using differential systems with stochastic coefficients and stochastic right hand side considering all input and output processes to be of the Markov type.
Klíčová slova:
random vibration; signal reconstruction; parametric noise; response asymmetry
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Asymmetry of the response probability density of a system with parametric random noises
Recording of time variable processes is accompanied by various internal disturbing effects as a rule. They influence parameters of the measuring facility, transducer-device transmission, etc. These ...
Basic biomechanical characterization of polyurethane based artificial cancellous structures
Šleichrt, Jan; Kytýř, Daniel; Pithartová, Kateřina; Senck, S.; Fürst, D.; Schrempf, A.
2018 - anglický
The main goal of this study is to validate elementary mechanical parameters of a newly designed open-cell foam. The purpouse for investigating artificial material is to approach the properties of the human bone in the case of its adequate replacement. Investigated material can be also used as an artificial bone to train surgical procedures and to improve the skills of the surgeons. Four sets of the foam with different chemical composition were subjected to an uniaxial quasi-static loading to describe basic mechanical behaviour of these samples. Based on these experiments, the stress-strain diagrams were created as a comparative tool including calculation of the effective Young’s modulus. The acquired knowledges will be used as input parameters of a follow-up study aimed at describing the morphology of presented structures and their response to mechanical experiments. A distortion effect of porosity on the results is not considered in this study.
Klíčová slova:
polyurethane foam; artificial bone; uniaxial loading; digital image correlation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Basic biomechanical characterization of polyurethane based artificial cancellous structures
The main goal of this study is to validate elementary mechanical parameters of a newly designed open-cell foam. The purpouse for investigating artificial material is to approach the properties of the ...
Instrumentation of four-point bending test during 4D computed tomography
Kytýř, Daniel; Fíla, Tomáš; Koudelka_ml., Petr; Kumpová, Ivana; Vopálenský, Michal; Vavro, Leona; Vavro, Martin
2018 - anglický
High-resolution time-lapse micro-focus X-ray computed tomography is an effective method for investigation of deformation processes on volumetric basis including fracture propagation characteristics of non-homogeneous materials subjected to mechanical loading. This experimental method requires implementation of specifically designed loading devices to X-ray imaging setups. In case of bending tests, our background research showed that no commercial solution allowing for reliable investigation of so called fracture process zone in quasi-brittle materials is currently available. Thus, this paper is focused on description of recently developed in-situ four-point bending loading device and its instrumentation for testing of quasi-brittle materials. Proof of concept together with the pilot experiments were successfully performed in a CT scanner TORATOM. Based on results of the pilot experiments, we demonstrate that crack development and propagation in a quasi-brittle material can be successfully observed in 3D using high resolution 4D micro-CT under loading.
Klíčová slova:
in-situ loading device; four-point bending; 4D micro-CT; crack propagation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Instrumentation of four-point bending test during 4D computed tomography
High-resolution time-lapse micro-focus X-ray computed tomography is an effective method for investigation of deformation processes on volumetric basis including fracture propagation characteristics of ...
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