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Asymmetry of the response probability density of a system with parametric random noises
Náprstek, Jiří; Fischer, Cyril
2018 - English
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.
Keywords:
random vibration; signal reconstruction; parametric noise; response asymmetry
Available at various institutes of the ASCR
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 - English
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.
Keywords:
polyurethane foam; artificial bone; uniaxial loading; digital image correlation
Available at various institutes of the ASCR
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 - English
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.
Keywords:
in-situ loading device; four-point bending; 4D micro-CT; crack propagation
Available at various institutes of the ASCR
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 ...
Corrosion products phase identification using micro-Raman and FTIR
Majtás, Dušan; Mácová, Petra
2018 - English
Phase identification of corroded metal objects might be problematic because corrosion products are usually a complex mixture of different phases. Furthermore, some of present phases may be either semi-crystalline or amorphous. The most suitable procedure is to use X-ray diffraction (XRD), for identification of crystalline phases in bulk, in combination with micro-Raman spectroscopy to obtain information on smaller scale and given location. Micro-Raman spectroscopy identifies crystalline and semi-crystalline phases. The literature also reports of the application of Mössbauer spectroscopy to identify amorphous phases. In this work, the combined use of Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy is evaluated. The methods may be interchangeable to some point. But is it safe to assume that all phases present can be detected?
Keywords:
corrosion; micro-Raman spectroscopy; FTIR
Available at various institutes of the ASCR
Corrosion products phase identification using micro-Raman and FTIR
Phase identification of corroded metal objects might be problematic because corrosion products are usually a complex mixture of different phases. Furthermore, some of present phases may be either ...
The effect of micro-silica on the microscopic features of the UHPC composite and its inter-facial transition zone
Hrbek, Vladimír; Prošek, Z.; Chylík, R.; Vráblík, L.
2018 - English
The uplift of concrete overall macroscopic performance by way of alternative additives is commonly used technique. In case of ultra high performance concrete (UHPC), micro-silica is added to the mixture as a micro-filler to the structure of cement binder. As a result, the cementitious matrix macro-mechanical performance is elevated. This paper is aimed on the UHPC micro-scale enhancement by different micro-silica additive content in the mixture. More closely, the study investigate the impact of the micro-silica on the inter-facial transition zone (ITZ) between the binder matrix and basaltic aggregate.
Keywords:
high performance concrete; indentation; spectral deconvolution SEM; image analysis; ITZ
Available at various institutes of the ASCR
The effect of micro-silica on the microscopic features of the UHPC composite and its inter-facial transition zone
The uplift of concrete overall macroscopic performance by way of alternative additives is commonly used technique. In case of ultra high performance concrete (UHPC), micro-silica is added to the ...
Design of material and technological copy for repair of sgraffito decorated renders
Válek, Jan; Skružná, Olga; Wichterlová, Z.; Waisserová, J.
2018 - English
This paper deals with research in Renaissance sgraffito materials and techniques. It focuses on the replication process for original materials and application techniques used in a reconstruction of the missing parts of a sgraffito decoration depicting a Landsknecht procession on the façade of a house in Slavonice. The result of the theoretical and practical experimental work is the description and evaluation of the process of creating a material and technological copy of the original. This involved detailed material analysis, determining the provenance of and selecting suitable raw materials, design of a repair mix and its testing, and evaluation during application trials. The study has shown that, in order to achieve good results, the conclusions of material analysis have to be linked to the practical\nskills of restorers and conservators. The particular application procedures that match the requirements of the historical material and the original work can be deduced from full scale practical trials. Feedback between the design of the repair mixture and the application process made it possible to come to an optimal material and application technique. The missing parts of the sgraffito were replaced using a mortar and application technique that closely correspond to those originally used in the Renaissance.
Keywords:
sgraffito; mortar analysis; historic techniques; Slavonice
Available at various institutes of the ASCR
Design of material and technological copy for repair of sgraffito decorated renders
This paper deals with research in Renaissance sgraffito materials and techniques. It focuses on the replication process for original materials and application techniques used in a reconstruction of ...
Engineering mechanics 2018. Book of full texts
Fischer, Cyril; Náprstek, Jiří
2018 - English
The proceedings contains papers presented at the 24th International Conference on Engineering Mechanics, which has been held in Svratka resort in Czech Republic under auspices of the Czech Society of Mechanics and being a part of IFTOMM (The International Federation for the Promotion of Mechanism and Machine Science) activities. As it corresponds with character of the conference, this proceedings consists of several topic oriented parts: Biomechanics, Fluid mechanics, Dynamics, Fracture mechanics, Kinematics, Mechatronics, Reliability of structures, Mechanics of solids, Techological processes, Thermodynamics. The volume represents a well-balanced overview of theoretical, numerical and experimental work on fundamental and applied studies.
Keywords:
mechanics; dynamics; reliability
Available at various institutes of the ASCR
Engineering mechanics 2018. Book of full texts
The proceedings contains papers presented at the 24th International Conference on Engineering Mechanics, which has been held in Svratka resort in Czech Republic under auspices of the Czech Society of ...
Forced movement of a ball in spherical cavity under kinematic excitation
Náprstek, Jiří; Fischer, Cyril
2018 - English
In the paper the response of a heavy ball rolling inside a semi-spherical cavity under horizontal kinematic excitation is investigated. The system with six degrees of freedom with three non-holonomic constraints is considered. The contact between the ball and the cavity surface is supposed to be perfect without any sliding. The mathematical model using the Appel-Gibbs function of acceleration energy is developed and discussed. The most important post-critical regimes are outlined and qualitatively evaluated on the frequency axis. Numerical experiments have been performed when excitation frequency is slowly swept up and down. Results obtained by means of semi-analytical investigation and numerical simulation are evaluated and physically interpreted. Some applications in civil engineering as a tuned mass damper used on slender structures is outlined. Strengths and weaknesses of solution method are evaluated.
Keywords:
nonlinear dynamics; non-holonomic systems; Appell-Gibbs formulation; singular states; tuned mass damper
Fulltext is available at external website.
Forced movement of a ball in spherical cavity under kinematic excitation
In the paper the response of a heavy ball rolling inside a semi-spherical cavity under horizontal kinematic excitation is investigated. The system with six degrees of freedom with three non-holonomic ...
Accuracy and numerical efficiency of approximate method for complex eigensolution of structure with specialized damping device
Hračov, Stanislav
2018 - English
The paper provides a detailed parametric analysis of the recently proposed approximate method for complex eigensolution of non-classically damped structures. This method is based on a combination of perturbation and incremental approaches and is applicable to the classically damped structures equipped with a specialized passive damping device. The numerical efficiency in terms of the required calculation times and the accuracy is demonstrated on a model of an existing structure for various combination of computational parameters. Wide numerical simulations revealed the selection of real eigenmodes of undamped system used in the approximate eigensolution as the most important parameter affecting the final accuracy.
Keywords:
non-classical damping; complex eigensolution; perturbation method; passive damper
Fulltext is available at external website.
Accuracy and numerical efficiency of approximate method for complex eigensolution of structure with specialized damping device
The paper provides a detailed parametric analysis of the recently proposed approximate method for complex eigensolution of non-classically damped structures. This method is based on a combination of ...
Influence of printing and loading direction on mechanical response in 3D printed models of human trabecular bone
Doktor, Tomáš; Kumpová, Ivana; Wroński, S.; Śniechowski, M.; Tarasiuk, J.; Forte, G.; Kytýř, Daniel
2018 - English
The paper deals with investigation on directional variations of mechanical response in 3D printed models of human trabecular bone. Sample of trabecular bone tissue was resected from human donor and 3D model was obtained by X-ray computed tomography. Then a series of cubical samples was prepared by additive manufacturing technique and tested by uniaxial compression loading mode. Mechanical response was compared in nine different combinations of direction of 3D printing and loading direction. The results show neglectible influence on the deformation response in elastic region (stiffness) and significant changes of the behaviour in plastic region (stress and strain at yield point, strain at full collapse).
Keywords:
additive manufacturing; tomography; deformation response
Available at various institutes of the ASCR
Influence of printing and loading direction on mechanical response in 3D printed models of human trabecular bone
The paper deals with investigation on directional variations of mechanical response in 3D printed models of human trabecular bone. Sample of trabecular bone tissue was resected from human donor and 3D ...
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