Lidé na fakultě
Ing. Jaroslav Valach, Ph.D.

2023, Young Transportation Engineers Conference 2022, Praha, České vysoké učení technické v Praze), p. 89-97), ISBN 978-80-01-07224-0, ISSN 2336-5382

The article presents a study of the mechanical processes occurring during the aluminothermic reaction using experimental methods (strain gauges, digital image correlation, thermography, scanning electron microscopy, profilometry). The aluminothermic reaction is a highly efficient welding method due to its exothermic behaviour, however, it places considerable demands not only on the welding technique, but also on the capabilities of the experimental methods used; these limitations are also discussed in the article. The aluminothermic reaction is associated with the formation of a localised heat source with a time evolution dictated by the technological procedure, which manifests itself in heat propagation to the surrounding weld material. The unequal evolution of the temperature field is the fundamental cause of the appearance of the heat affected zone or local deformations or surface curvature, which was the focus of the experimental methods deployed above and the results of which are shown in the article.

Stať ve sborníku z prestižní konf. (Scopus)

2017, Advanced Engineering Materials, 19 (10), ISSN 1438-1656

In this paper, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatine. Samples from each group are tested under quasi-static loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasi-static and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05–1.4, whereas the effect of gelatine leads to increase of only 5–10%. Analysis of the Poisson's function reveals influence of filling on achievable (negative) values of Poisson's ratio, when compared to unfilled specimens. The results for the Poisson's function yielded apparently different values as the assessed minima of quasi-static Poisson's ratio in small deformations are constrained by a factor of 15.

Článek v periodiku excerpovaném SCI Expanded

2015, Příspěvek technických věd k záchraně a restaurování památek, Praha, Ústav teoretické a aplikované mechaniky AV ČR, v. v. i.), p. 95-106), ISBN 978-80-86246-43-7

Ochrana stavebních památek vyžaduje speciální přístup s ohledem na potřeby zachování hodnoty objektů. Naneštěstí chybí systematicky utříděné a snadno dostupné poznatky o podstatě a příčinách poškození historických objektů. Tuto situaci může překonat představený systém MONDIS, který pomocí sémantických technologií popisuje poškození od jejich projevu, přes jejich příčinné souvislosti až po návrh zásahu. Jeho součástí je také mobilní aplikace umožňující provádět průzkum poškození přímo v terénu

Kapitola v jiné knize česky

2015, ISBN 978-80-86246-43-7

Kniha přináší přehled vybraných výsledků nedávného mezioborového výzkumu na pracovištích Ústavu teoretické a aplikované mechaniky AV ČR, v. v. i., v moderně rozvíjené oblasti památkových věd. Památkové vědy patří mezi mladší vědecké obory, jejichž vývoj je silně ovlivněn současným bouřlivým rozvojem informačních technologií, miniaturizací a pokročilostí výrobních postupů, které jsou podmínkou aplikace metod a technik dříve pro památkovou péči nedosažitelných. Prolomení technických i ekonomických bariér umožňuje využívání nanomateriálů a nanotechnologií pro záchranu, zachování i zhodnocení památkových a dalších historických objektů.

Kniha - sborník, česky

2014, 9th International Conference on Local Mechanical Properties, Zürich, Transtech Publications), p. 257-260), ISBN 978-3-03785-876-9, ISSN 1013-9826

The paper presents application on digital image correlation (DIC) and microindentation for investigation of plastic flow under Brinell ball indenter applied on steel specimen made of two screwed together parts. Specimens in two different material state (a) as delivered (b) annealed were investigated. This approach enables internal surface to act as the external one and to be examined by mentioned methods. Results obtained by application of DIC on scanning electron microscope (SEM) images are compared to microhardness maps and agreement is demonstrated.

Stať ve sborníku z prestižní konf.

2014, Local Mechanical Properties X, Zurich, TRANS TECH PUBLICATIONS LTD), p. 245-248), ISBN 978-3-03835-062-0, ISSN 1013-9826

This study is focused on inspection of damage extent induced into C/PPS composite material by fatigue and impact loading. Initial damage to specimens was induced by drop-weight out-of-plane impact damage. Several levels of damage states (intact specimen, fatigued and impacted specimen, ruptured specimen) were inspected using modulus mapping (MM) technique. Quantification of the damage level was based on comparison of results from MM obtained in distinct locations on the specimens. Regions of interest were selected in order to determine magnitude of damage after impact and to assess remaining loading capabilities of the material. For this purpose, material maps provided information about location where matrix had been inflicted by the damage. Results show that impact loading has no measurable influence on mechanical properties of the matrix. However, gradient in mechanical properties was detected in the vicinity of crack. Results were validated using quasi-static nanoindentation and constant strain rate continuous measurement that showed depth profile of mechanical properties.

Stať ve sborníku z mezinár. konf.

2014, Key Engineering Materials, Zurich, TRANS TECH PUBLICATIONS LTD), p. 186-189), ISBN 978-3-03785-876-9, ISSN 1013-9826

In the case of material parameters required for evaluation of built heritage preservation state, knowledge of the least possible volume of removed sample is essential in order to minimize damage accumulation to the buildings. These requirements lead to determination of representative volume element (RVE) that was in this paper calculated using combination of image and signal processing techniques. Then, a detailed map of material properties was created using nanoindentation to evaluate local characteristics of the material. Furthermore, atomic composition of samples was quantified by energy dispersive spectrometry (EDX) detector for scanning electron microscopy (SEM) device. Presented method based on combination of SEM, EDX and nanoindentation techniques demonstrates possibility of effective testing in the field of historical buildings preservation.

Stať ve sborníku z prestižní konf.

2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)

Evaluation of natural frequencies‘ shift during thermal loading of carbon fibre/polyphenylene sulphide (C/PPS) composites used in aircraft industry is described in this paper. Values of natural frequencies were chosen as indicators of changes in material properties. Custom-designed experimental device suitable for determination of specimen's natural frequencies was developed according to operation in thermal chamber. During the experiment steel pellets were dropped on specimen. Overall acoustic response of the impact was recorded by microphone. Two characteristic natural frequencies were evaluated using spectral analysis of recorded sound. Series of measurements at different temperatures were performed nearly up to the temperature of PPS glass-transition. Obtained results show strong correlation between natural frequency shift and temperature of the specimen’s surface.

Stať ve sborníku z mezinár. konf.

2013, Proceedings of 12th Youth Symposium on Experimental Solid Mechanics, Bari, Politecnico di Bari)

Presented article is focused on plastic strain distribution assessed by microindentation technique. If the nature of the specimen is unsuitable for radiological inspection destructive sample preparation is inevitable to describe its inner state. Two mutually perpendicular planes in deformed zone were manufactured by electrical discharge machining and polishing. One of the planes was created prior the loading procedure and during the loading the parts were connected by screws. In the perpendicular plane the specimen was cut after the loading. Specimens prepared using this procedure were then subjected to microindentation testing. Each set of indents consisted of approximately 150 Vickers microindents covering area of 0.5 mm2. Images of imprint arrays on the specimens surface were acquired by scanning electron microscope. Diagonals of indents were determined and then Vickers hardness values were calculated. Map of hardness distribution was created using cubic interpolation method.

Stať ve sborníku z mezinár. konf.

2013, UPB Scientific Bulletin, Series D: Mechanical Engineering, 75 (1), p. 161-170), ISSN 1454-2358

During the last decades, there has been much effort on the determination of effective elastic properties of porous metals. In this paper, the overall elastic moduli of reference aluminium foam Alporas are assessed using predictive methods based on definition of compliance contribution tensor. Surface of the foam is captured using flatbed scanner and such data is subjected to image and signal processing routines in order to obtain dimensions of the sufficient representative volume element and calculation of structural characteristics for analytical homogenization. It is shown that from all considered homogenization models only the Mori-Tanaka scheme gives results reasonably close to nominal values.

Článek v periodiku excerpovaném databází Scopus

2013, UPB Scientific Bulletin, Series D: Mechanical Engineering, 75 (2), p. 157-164), ISSN 1454-2358

Carbon fibre in polyphenylene sulfide composites became popular ma- terial in aircraft industry but its fragility and low resistance against impact load- ing limits the application of these composites in aircraft primary structures. The article deals with experimental investigation of the mechanical response of dam- aged composite. Material degradation of intact and damaged specimens during fatigue tests was investigated. The changes in natural frequencies, ultrasound wave propagation and bending stiffness were chosen as damage parameters. The entire fatigue life of intact and damaged specimens was studied in the article by all the presented methods. The accuracy and reliability of assessment of damage parameters were compared. Comparison of accuracy and reliability of presented method for assessment of damage parameters is also given.

Článek v periodiku excerpovaném databází Scopus

2013, Proceedings of 30th Danubia - Adria Symposium on Advances in Experimental Mechanics, Zagreb, Croatian Society of Mechanics), p. 43-44), ISBN 978-953-7539-17-7

In this paper, application of laser profilometry is demonstrated for surface geometry measurement and compared to results obtained by active thermography as a reference method for damage detection and assessment. Specimens made of eight-ply carbon fiber reinforced PPS matrix laminate in the form of strips 25mm wide, 250mm long and 2mm thick were subjected to simulated impact damage. Both mothods are capable to detect impacts, which is first sign of incurred damage of material. Therefore this methods are suitable for monitoring of damage accumulation during fatigue process.

Abstrakt ve sborníku z mezinár. konf.

2013, Proceedings of 12th International Workshop on Advanced Infrared Technology and Applications, Politecnico di Torino), p. 217-219)

The presented work summarizes first results on hi-speed thermography analysis of cyclic loading of carbon fibers reinforced thermoplastic matrix composite. Opportunity to record and analyze minute changes of temperature is shown as well as detailed documentation of energy dumping on gradual increase of mean temperature of the specimen. Demonstrated sensitivity of the thermoanalysis is prerequisite for future investigation of impact damage as discussed in conclusions.

Abstrakt ve sborníku z mezinár. konf.

2012, Chemické listy, 106 (s3), p. 399-400), ISSN 0009-2770

The article deals with monitoring of degradation of carbon fibre reinforced polymer (CFRP) under cyclic loading. The investigated material is composed of polyphenylensulfid matrix and carbon fibres. Four specimens were subjected to repeated cyclic loading. During the fatigue loading surface of tested specimens was observed by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) to obtain surface roughness characteristics and micrographs of surface morphology. With increasing number of cycles the measured surface characteristics showed increasing surface roughness indicating at the level of micromechanics detachment of matrix from the fibers and also changes in the matrix structure itself.

Článek v periodiku excerpovaném SCI Expanded

2012, Engineering Mechanics 2012, Prague, Institute of Theoretical and Applied Mechanics, AS CR), p. 231-237), ISBN 978-80-86246-39-0

Assessment of degradation rate of material can be carried out by many experimental techniques differing in complexity and sophistication. A relatively simple method based on acoustic analysis is described in this contribution. Degradation of material's properties due to fatigue loading is detectable in decrease of their modulus of elasticity that can be derived from natural frequencies of specimens, which were acquired by the presented method. These measurements utilize self-designed device capable of specimen excitation and acquisition of its vibration. The recorded signal is then processed by spectral analysis enabling determination of natural frequencies. Usefulness of the above mentioned acoustic method can be seen in the fact that the measured changes of material's parameters are comparable to those obtained by laser vibrometry, which is by several orders more expensive technique.

Stať ve sborníku z mezinár. konf. cizojazyčně

2012, Chemické listy, 106 (S3), p. 523-524), ISSN 0009-2770

The leech's sucking apparatus is an amazing instrument - it has 3 jaws and 300 teeth made for easily cut into the skin of the host animal. In this study, we used nanoindentation and atomic spectroscopy to reveal composition and material properties of leeches' teeth. Five samples of leech's jaws obtained from adult subjects of Hemopis sanguisuga were investigated. Main constituents of leeches' teeth have been identified. The tooth is composed mainly of calcium (41.9%), oxygen (41.2%) and carbon (11.4%), other constituents are present in small quantities (F, Na, P, 0 and S), therefore, a substance typical for mineral component in bones hydroxyapatite is likely present in the teeth among other substances. Material properties, which are independent on indentation depth, examined by nanoindentation provided average reduced modulus Er = 27.54 +/- 3.71GPa

Článek v periodiku excerpovaném SCI Expanded

2012, Chemické listy, 106 (S3), p. 551-554), ISSN 0009-2770

The paper presents enhanced method for study of severe plastic deformation by hardness mapping utilizing portable hardness tester, flatbed scanner and software processing tool. This technique can be advantageous in situations, where crude information is not only sufficient, but also preferred, especially when it concerns testing on-site and on medium to large scale specimens and construction. Validity of the approach is supported by a comparison of hardness mapping results to the results obtained by an independent method based on evaluation of plastic strains from thermograms. It is shown that both methods determined similar shape and the extent of the plastic zone of the studied specimens.

Článek v periodiku excerpovaném SCI Expanded

2012

Tato práce se zabývá nedestruktivním testováním uhlíkového kompozitu s polymerní matricí C/PPS. Za tímto účelem byla zvolena metoda určování degradace materiálu pomocí akustických charakteristik. Tato metoda byla významně upravena, bylo zkonstruováno vlastní experimentální zařízení a vyvinut vlastní software pro měření a vyhodnocování dat. Pomocí těchto nástrojů byly evaluovány vlastní frekvence vzorku a jejich logaritmický dekrement útlumu. Měřené změny těchto veličin byly následně použity jako indikátory poškození materiálu únavovou degradací.

Diplomová práce

2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 244-250), ISBN 978-1-63439-432-1

During the last decades, there has been much effort on the determination of effective elastic properties of porous metals. In this paper, the overall elastic moduli of reference aluminium foam Alporas are assessed using predictive methods based on definition of compliance contribution tensor. Surface of the foam is captured using flatbed scanner and such data are subjected to image and signal processing routines in order to obtain dimensions of the sufficient representative volume element and calculation of structural characteristics for analytical homogenization. It is shown that only the Mori-Tanaka scheme gives results close to nominal values.

Stať ve sborníku z mezinár. konf.

2012

Thesis is aimed at the determination of effective mechanical properties of foam materials with concentration on metal foams. Elastic constants are investigated using numerical homogenization method. As a input data, 2-D macrostructure of the reference foam Alporas captured by high resolution flatbed scanner was used. The acquired image is segmented to binary one that is subjected to spectral analysis in order to assess dimensions of the representative volume element sufficient for characterization of the random microstructure of the foam. The real form of the microstructure is substituted by equivalent Voronoi diagram that is consequently transformed to finite element model. The model is used in a set of simulated mechanical tests in ANSYS software leading to determination of searched elastic constants. Obtained results are compared with the experimental ones assessed using tension test performed with the Alporas specimen.

Diplomová práce

2012, Proceedings of 11th Youth Symposium on Experimental Solid Mechanics, Brašov, Universitate Transilvania Brasov), p. 92-95), ISBN 978-1-63439-432-1

Abstract: This paper deals with investigation of acoustic material degradation indicator (natural frequency) of carbon fibre C/PPS composite obtained by a custom-built experimental device. The specimen's sound was emitted during the impact of steel pellet in acoustic measurement experimental device. Acoustic signals were recorded and analyzed using spectral and regression analysis. Specimens were repetitively measured after designated number of loading cycles. The decreases of natural frequencies were determined for given number of natural modes. Relations between natural frequency values and their decreases were investigated. To conclude, the data assessed using acoustic measurements are suitable for evaluation of material degradation.

Stať ve sborníku z mezinár. konf.

2012, e-Journal of NDT, 17 (10), ISSN 1435-4934

In this paper the application of quantitative thermography analysis on strains is presented on the study dealing with evaluation of material's behavior during plastic deformation of specimen in two thermodynamically different states. The analysis of plastic deformation and thermal phenomena processes is demonstrated on compact-tension steel specimens both in theoretical and experimental way. The experiments proved different temperature response to external loading and dependence of plastic deformation development on material's state. These results support claim that thermography can be used for non-destructive investigation of internal state of materials.

Článek v odborném recenzovaném periodiku

2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 31-34), ISBN 978-80-01-05062-0

This paper deals with evaluation of hardness fields using Vickers indentation device and a semi-automatic software tool for local hardness distribution mapping. Specimens from low carbon pipeline steels were investigated. Dense grids of Vickers imprints were created on the specimens' surface. Image data of the surface were acquired by a high resolution flatbed scanner with resolution 6400dpi. The imprints were measured using an custom-developed image processing tool, and from the obtained geometrical characteristics local hardness values were derived. From the local hardness values and their coordinates the hardness field in the whole specimen was interpolated.

Stať ve sborníku z mezinár. konf. cizojazyčně

2012, Experimental Methods and Numerical Simulation in Engineering Sciences, Proceedings of XIIIth Bilateral Czech/German Symposium, Praha, České vysoké učení technické v Praze, Fakulta dopravní), p. 35-38), ISBN 978-80-01-05062-0

This paper deals with investigation of acoustic material degradation indicator (attenuation decrement drop of selected natural frequency) measured by a custom-built experimental device. Samples of C/PPS fibre composite material were analyzed. Acoustic signals were recorded and processed using spectral analysis and sound signal regression. Data measured by this method were verified by comparative experiment. Specimens were simultaneously measured using both acoustic experimental device and laser vibrometer. Modal analysis of the specimen were carried out prior to the experiment. This enabled assessment of specimens natural modes and therefore the best impact zone. In total, 10 measurements were performed for each specimen at the same level of degradation. Measured data were then processed and compared. The specimens were repetitively measured after designated number of loading cycles. To conclude, the data assessed using acoustic measurements are comparable in terms of precision, reproducibility and reliability with results from laser vibrometer and the method is suitable for evaluation of material degradation.

Stať ve sborníku z mezinár. konf. cizojazyčně

2011, Engineering Mechanics 2011, Praha, Ústav termomechaniky AV ČR), p. 355-358), ISBN 978-80-87012-33-8

Changes of mechanical properties, namely of modulus of elasticity, often play a role of damage accumulation indicators in the framework of fatigue behaviour of composite materials. In order to improve the reliability of these indicators for identification of material degradation process it is necessary to eliminate the influence of external loading and volume forces associated with thermal expansion of heterogeneous material at various temperatures. Therefore the paper deals with description of experimental assessment of relation between external load and material stiffness and also studies the dependency of material stiffness on temperature. For the monitoring of degradation process ultrasonic measurement was used. Obtained results are discussed with respect to fatigue testing of material and also interpreted from the micromechanical point of view.

Stať ve sborníku z mezinár. konf. cizojazyčně

2011, Chemické listy, 105 (17), p. 729-732), ISSN 0009-2770

The presented paper outlines experimental investigation that is a part of an extensive research plan of study of fatigue properties of aerospace industry grade CRFP laminates. These materials are relatively novel and their long-term behavior and degradation are not yet completely described. Deterioration of this complex material in cyclic loading conditions is to be evaluated by several criteria based on evolution of certain of mechanical properties. Among the criteria is a decrease of modulus of elasticity. In order to reliably detect the changes in this property sensitive three point bending experimental setup was prepared, calibrated and compared to the results of the independent ultrasound method yielding the dynamical modulus of elasticity. Simultaneously, the local mechanical properties were studied by nanoindentation in order to set a reference point for a successive measurement after fatigue tests.

Článek v periodiku excerpovaném SCI Expanded

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 64-65), ISBN 978-1-63439-434-5

This paper is aimed at the study of mechanical behavior of aluminium metal foams by modeling their internal structure and analysis using finite element method. Alporas aluminium foam was selected as a reference material and the material characteristics are derived from tensile loading using numerical FEM analysis in ANSYS software. Internal structure is modeled by 2 different methods - using voxel model created on the basis of a series of CT scans and by discretization using Gibson-Ashby's cellular model. Mechanical behavior analysis is performed in both elastic and plastic fields. Investigated mechanical characteristics are particularly the evolution of overall Young's modulus according to different relative densities and in the plastic field tensional stress-strain diagram. The beam-only discretization is considered intentionally to investigate its suitability for modeling of closed cell foams. Finally, FEM numerical results are compared to Gibson-Ashby's mathematical model.

Stať ve sborníku z mezinár. konf.

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 71-72), ISBN 978-1-63439-434-5

Article deals with describing of the pre-testing procedure for the uniaxial testing, nanoindentation and finite element modeling of single trabeculae. The first part is focused on the specimen resection, delipidation and fixation in a novel high precision experimental device which enables to measure the strains optically using a high-resolution CCD camera. The second part deals with the development of the volumetric model of the trabecula required for numerical analysis. The last part is dedicated to optimization of polishing procedure used sample surface preparation for nanoindentation. Effect of the grain size, load and duration time of the grinding on final surface roughness was analyzed. Change in the surface roughness was monitored during the preparation process using a confocal microscope. Optimized procedure of sample preparation for micro-mechanical testing with satisfactory results is presented in the paper.

Stať ve sborníku z mezinár. konf.

2011, 10th Youth Symposium on Experimental Solid Mechanics, Chemnitz, Technische Universität Chemnitz), p. 45-46), ISBN 978-1-63439-434-5

This article is focused on assessment of pore size distribution of a porous material. Improvements of the analysis procedure and of the software tools are presented. For the comparison of reliability of the presented method specimena of various origins were tested. As representatives of biological materials specimena of human and porcine trabecular bone were tested, as representatives of artificial materials synthetic pumice and frit glass were used. Images required for the image analysis were captured using a CCD camera, a high resolution flatbed scanner and a confocal microscope. The different methods used to acquire the images are discussed regarding to the range of the pore size, dimensions of the available specimen and properties of the specimen surface. Used image processing algorithms were tested and improved regarding to the variable shape of the voids present in the material structure.

Stať ve sborníku z mezinár. konf.

2011, Experimentální analýza napětí 2011, Brno, Brno University of Technology), p. 49-55), ISBN 978-80-214-4275-7

The article deals with assessment of fatigue degradation of C/PPS composites using simple acoustic measurement technique. Changes in natural frequency and attenuation decrement were chosen as indicators of fatigue damage accumulation in the studied composite material. New testing device was developed for acoustic measurement. The experimental setup was designed to chime the specimen by repeatable force of stiff striker exciting a specific natural mode of vibration and to record the acoustic response of the specimen to the impact simultaneously. From the power spectral density of the signal the natural frequency was obtained. Using the same signal, the attenuation decrement was estimated from regression of the its envelope. Presented high precision non-destructive method allows to conclusively measure the natural frequency and its change with a deviation smaller than a few tenths per cents.

Stať ve sborníku z mezinár. konf. cizojazyčně

2011, Engineering Mechanics 2011, Praha, Ústav termomechaniky AV ČR), p. 115-118), ISBN 978-80-87012-33-8

This paper deals with pore size distribution assessment of trabecular structure of human proximal femur. Two distinct methods for estimation of the pore size distribution histograms are tested, mercury intrusion porosimetry and image analysis. For the image analysis two-dimensional images of crosssections of the specimens were used and the pore size distribution was estimated using a stereological calculation method based on the geometrical properties of an idealized pore. Comparison of the results of both methods is presented. Suitability of both methods for biological materials is discussed regarding to mechanical properties of these materials, characteristics of pores and range of pore sizes present in the structure.

Stať ve sborníku z mezinár. konf. cizojazyčně

2011, 19th Annual Conference Proceedings Technical Computing Prague 2011, Praha, Vydavatelství VŠCHT Praha), p. 53-56), ISBN 978-80-7080-794-1

This article presents the implementation of a non-invasive optical method - Digital Image Correlation. First it discusses the basic principle of how the DIC works, covers to innovative improvements like the process of subpixel approximation, global data smoothing and process of image sequencing. The presented DIC application is compared to other commercial applications and systems. The application is provided with the GUI, which enables easy to learn and simple usage for the novice user. The output of the application contains the 2D plots of displacement and strain fields.

Stať ve sborníku z mezinár. konf. cizojazyčně

2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 155-157), ISBN 978-88-95940-30-4

Article deals with pore size distribution assessment of porous materials using image analysis. Test samples used in the study were prepared from metal foams and porcine trabecular bone. Two- and threedimensional images were obtained by SEM (scanning electron microscopy) and a high resolution flatbed scanner. For the pore size distribution assessment various methods were used, depending on input data properties (method of obtainig image data) and on pores characteristics (different approach should be used for closed or opened pores). For pore size evaluation using 2D images 25F Association method [5] was used. For verification of the developed algorithms MIP (mercury intrusion porosimetry) measurements were performed, but only in case of trabecular bone samples, because opened pores are necessary for these measurements. Presented algorithms were verified using artificial data structures.

Stať ve sborníku z mezinár. konf.

2010, Experimental methods and numerical simulation in engineering sciences, Wuppertal, Bergische Universität Wuppertal), p. 52-53)

Development of the presented method is a part of the complex program devoted to the investigation of the fracture properties of ductile metals in the states far from the applicability of the linear fracture mechanics theory. The method combines experimental and numerical techniques for detailed study of behavior of ductile specimens in loading preceding failure. The experimental part of the method is based on simultaneous measurement of displacements on the specimen surface by the digital image correlation method and also on recording of the temperature field of the speci-men, as the temperature field is an important variable influencing crack behavior. The displacements and temperatures are then combined in the finite elements model used for calculation of other relevant properties for description of the deformation process. The method is intended for evaluation of fracture mechanics criteria and for study of brittle to ductile transition of materials.

Stať ve sborníku z mezinár. konf.

2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 29-31), ISBN 978-88-95940-30-4

The aim of research is to develop a reliable method for studying of evolution of plastic deformation during the loading process by comparing temperature field measured by thermo-camera with FEA model on CT specimens. The presented method is noninvasive and non-contact. For strain measurement is used thermoplastic phenomenon, which is a typical for local raise of the temperature in deformed places. The loads and the boundary conditions used in the experiments are input to the mechanical FEA model and after analysis we can compare the computed density of the plastic work with the density of heat energy known from experiment. The FEA model and the experiment yield similar results. The description and modeling of regions far away from the notch involves consideration of more complex physics (transition phenomena) therefore the differences of maximum values of heat between experiment and simplified model are bigger.

Stať ve sborníku z mezinár. konf.

2010, 9th Youth Symposium on Experimental Solid Mechanics, Trieste, University Trieste), p. 158-160), ISBN 978-88-95940-30-4

This contribution presents application of digital correlation method for optical measurement of displacements and techniques for improvement of data processing. The main point of the paper is a comparison of two different techniques of the data processing of the same experiment. First one is based on determination of the displacement field using the image of studied body surface at the beginning and at the end of load application, while the second evaluation technique relies on sequential evaluation and addition of the partial displacement fields derived from comparison of adjacent image pairs in the sequence. It is shown that the later approach is favorable from the point of view of the total error of the experimental results. This observation is especially true in the case of large deformations as explained in the final discussion of the paper.

Stať ve sborníku z mezinár. konf.

2009, 8th Youth Symposium on Experimental Solid Mechanics, Budapešť, Scientific Society of Mechanical Engineers), ISBN 978-963-9058-26-2

Article deals with investigation of physical and mechanical properties of trabecular bone. Non-destructive ultrasonic tests and heat measurements were used to determine the modulus of elasticity of each sample. The velocity of longitudinal ultrasonic waves' propagation depends on the mechanical properties of the material, so the Young's modulus can be obtained from the formula coupling elasticity modulus, wave velocity and bone density.

Stať ve sborníku z mezinár. konf.

2008, Československý časopis pro fyziku, 58 (1), p. 58-63), ISSN 0009-0700

Legující přísady přísady nejsou v kovových slitinách rozděleny rovnoměrně. Jejich koncentrace se liší zrno od zrna. Při mikroradiografikém pozorování se nestejnoměrná koncetrace těchto přísad v jednotlivých zrnech slitiny projevuje charakteristickou stuktrurou. Po vhodném zpracováním dat je tak možné určit percentuální rozložení hlavních přísad v pozorovaném radiogramu.

Článek v odborném recenzovaném periodiku česky