National Repository of Grey Literature 54 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
Knowledge Extraction from Data
Kozák, Vladislav ; Mrázová, Iveta (advisor) ; Petříčková, Zuzana (referee)
The task of this master thesis is to describe the overall process of data mining and algorithms used for data preparation and data modelling. The qualities of these algorithms are compared and the results are well-founded with repeatable tests. Knowledge gained by this research is applied to 2 real data based tasks. Master thesis includes development of own data mining application. The stress was laid on robustness, intuitive GUI as well as wide spectrum of data mining algorithms implemented.
Information system for schools
Kozák, Vladislav ; Patočka, Mikuláš (advisor) ; Zavoral, Filip (referee)
The task of the work is to develop information system for primary and secondary schools. The application allows to insert and store data related with school and performs mass printing of school reports. The user interface is easy to use and includes grafic interface for setting the printer output. The application comunicates with database server and supports parallel access.
Method of Threshold Stress Determination for a Local Approach to Cleavage Fracture
Kotrechko, S. ; Gryshchenko, V. ; Kozák, Vladislav ; Dlouhý, Ivo
The contribution is focused on a new methodology description for determination of threshold stress sigma th, as the third parameter in Beremin local approach to cleavage fracture that is using three-parameter Weibull statistics. Nature of the methodology lies in tensile testing of rounded notched specimens at liquid nitrogen temperature and corresponding calculations. Reactor pressure vessel steel was chosen as an example for the illustration.
Prediction of the Traction Separation Law of Ceramics Using Iterative Finite Element Modelling
Kozák, Vladislav ; Chlup, Zdeněk ; Padělek, P. ; Dlouhý, Ivo
Specific silicon nitride ceramics, the influence of the grain size and orientation on the bridging mechanisms was found. In ceramic matrix composites, crack-bridging mechanisms can provide substantial toughness enhancement coupled with the same and/or increased strength. The prediction of the crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated. From a number of damage concepts the cohesive models seem to be especially attractive for the practical applications. Within the standard finite element package Abaqus a new finite element has been developed; it is written via the UEL (user’s element) procedure. Its shape can be modified according to the experimental data for the set of ceramics and composites. The element seems to be very stable from the numerical point a view. The shape of the traction separation law for four experimental materials is estimated via the iterative procedure based on the FEM modeling and experimentally determined displacement in indentation experiments, J-R curve is predicted and stability of the bridging law is tested.
Information system for schools
Kozák, Vladislav ; Zavoral, Filip (referee) ; Patočka, Mikuláš (advisor)
The task of the work is to develop information system for primary and secondary schools. The application allows to insert and store data related with school and performs mass printing of school reports. The user interface is easy to use and includes grafic interface for setting the printer output. The application comunicates with database server and supports parallel access.
Knowledge Extraction from Data
Kozák, Vladislav ; Petříčková, Zuzana (referee) ; Mrázová, Iveta (advisor)
The task of this master thesis is to describe the overall process of data mining and algorithms used for data preparation and data modelling. The qualities of these algorithms are compared and the results are well-founded with repeatable tests. Knowledge gained by this research is applied to 2 real data based tasks. Master thesis includes development of own data mining application. The stress was laid on robustness, intuitive GUI as well as wide spectrum of data mining algorithms implemented.
Modelling of ductile fracture for sub-sized three-point-bend geometry
Stratil, Luděk ; Hadraba, Hynek ; Kozák, Vladislav ; Dlouhý, Ivo
The contribution deals with the simulation of R-curve using complete Gurson model of ductile fracture. The R-curve was experimentally determined for a Eurofer97 steel on sub-sized three-point-bend geometry in previous study. To apply complete Gurson model the parameters describing the voids´ behaviour and characteristic length parameter need to be determined. The nucleation parameters were identified by single specimen method of smooth tensile test specimen and from metallographic examination of fracture micro-mechanism. The characteristic length parameter was derived by fitting load versus deflection curves of sub-sized specimens. The simulations of the tests were carried out by software ABAQUS in Standard and Explicit modules. The identification was supported by parametric studies. Comparing experimental and simulated R-curve the ductile tearing was not successfully achieved. Insufficient calibrated parameters as a result non-uniqueness problem of single specimen method were found.
A simulation of R-curve by complete Gurson model
Stratil, Luděk ; Hadraba, Hynek ; Kozák, Vladislav ; Dlouhý, Ivo
The contribution deals with the simulation of R-curve using completed Gruson model of ductile fracture. The R-curve was experimentally determined for a Eurofer97 steel in previous study. The simulations of the tests were carried out by FEM software ABAQUS 6.11 in Standard and Explicit modules. The Gurson parameters were identified by single specimen method of smooth tensile test specimen and from metallographic examination of fracture micro-mechanism. The identification was supported by parametric studies. Comparing experimental and simulated R-curve the ductile tearing was not successfully achieved. Insufficient calibrated parameters as a result non-uniqueness problem of single specimen method were found.
Fatigue crack growth and delamination in fiber metal laminate (GLARE) during loading with positive mean stress
Chlupová, Alice ; Kozák, Vladislav
The aim of the paper is to present the results of a study on the damage of fiber metal laminate (GLARE) subjected to the low cycle fatigue loading with positive mean stress. The fatigue crack initiation and growth was observed on the surface of notched specimens and then the individual layers of fatigued specimens were removed by chemical etching and polishing to obtain data about cracks length and delamination shape and area. Mechanism of initiation and crack growth in this type of materials differs from homogeneous monolithic materials. The fatigue life in term of number of cycles to crack initiation depending on amplitude of local plastic deformation and local stress in the notch root was evaluated.
Stress state analysis of sub-sized pre-cracked three-point-bend specimen
Stratil, Luděk ; Kozák, Vladislav ; Hadraba, Hynek ; Dlouhý, Ivo
The contribution deals with finite element analysis of stress state in sub-sized pre-cracked three-point bend specimen (KLST). A studied material was Eurofer´97 steel. The true stress-true strain curve was obtained from tensile test. The three point bend tests were carried out on plain and side-grooved specimens at ambient temperature and were simulated using ABAQUS 6.10. The stress state in KLST specimen was compared with the stress state of standard specimen. The analysis confirmed the stress state in KLST specimens at the crack tip does not correspond to conditions of standard fracture toughness determination because loss of constraint.

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