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Multiplatformní mobilní aplikace pro nákup kuponů
Ševčík, Martin
This thesis describes design and implementation of cross platform mobile application for coupon purchasing in the Vykupto company. First part analyzes the existing mobile Vykupto applications. New application's draft including visual application screens is created on basis of requested functional and non-functional requirements. The following part is about selecting appropriate technology to create cross-platform application. The last part covers implementation of a application prototype and user testing.
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On a critical geometry of a crack arrested at a bimaterial interface
Ševčík, Martin ; Zouhar, Michal ; Máša, Bohuslav ; Hutař, Pavel ; Náhlík, Luboš
Surface crack propagation in a thin soft protective layer on a massive stiffer substrate is analyzed using generalized linear elastic fracture mechanics. The growth of the initial crack is considered in both forward and sideways directions and the influence of the interface between the protective layer and massive substrate on the final crack configuration is investigated. It is shown that, depending on the elastic mismatch, the part of the crack front can be arrested at the interface protective layer/substrate and the rest of the crack grows continuously sideways only. The effective value of the stress intensity factor is used in order to predict the conditions under which the crack will propagate through the interface into the second material. Corresponding calculations have been made by finite element method.
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Numerical modelling of damage of a particulate composite with polymer matrix
Máša, Bohuslav ; Ševčík, Martin ; Náhlík, Luboš
The main focus of this contribution is estimation of mechanical properties of a composite loaded in tension using finite element method. Investigated composite is composed of matrix in a rubbery state filled by alumina-based particles (Al2O3). Hyperelastic properties of the matrix have been modelled by the Mooney-Rivlin material model. The damage mechanisms of the matrix have also been taken into account. Results of numerical analyses have been compared with experimental data and good agreement between numerical models with damage mechanisms of matrix and experimental data has been found.
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Crack stability condition at the interface between two polymer materials
Zouhar, Michal ; Hutař, Pavel ; Náhlík, Luboš ; Ševčík, Martin ; Knésl, Zdeněk
The aim of this work is to study the behaviour of crack with its tip at the interface of two polymer materials. The numerical model of cracked bi-material tension specimen is investigated and a stability criterion was tested. Usually a stability criterion based on general stress concentrator needs the relation between critical value of the generalized stress intensity factor and critical value of the stress intensity factor (fracture toughness). This relation is a function of elastic mismatch between particular materials, fracture toughness of the main material and critical distance d. Estimation of d is usually not straightforward and different authors use different approaches for its determination. Therefore main aim of this study is mutual comparison of published approaches for d estimation and to quantify their effect on the critical loading value. The results of this study can lead to better lifetime prediction and design of layered structures.
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Influence of point load on crack shape in polymeric pipe
Ševčík, Martin ; Hutař, Pavel ; Náhlík, Luboš ; Pinter, G. ; Frank, A.
The aim of this work was to develop an easy applicable algorithm of numerical model creation simulating a cracked polymeric pipe under various combination of loading. Proposed algorithm is able to find a real crack front shape using iterative procedure. The main aim was to study the effect of the point load and its consequences on the crack front shape. It was numerically confirmed that point loading causes grater crack extension in axial direction than in the case of pipe loaded by pure inner pressure. This results leads to higher stress intensity factor and lower residual life-time of the pipe system.
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Simulation of the crack growth in the weld of the polyolefin pipes
Ševčík, Martin ; Hutař, Pavel ; Náhlík, Luboš
The aim of this work was to study the effect of the material properties change due to the butt welding on the stress intensity factor in polyolefin pipe. The gradient change of the Young’s modulus was assumed. The crack was located in the middle of the affected zone. The stress intensity factors estimated in both graded region and basic material (homogenous case) were compared. Strong influence of the graded region on the value of the stress intensity factor was observed. Therefore, for realistic estimation of the welded pipe lifetime the change of the material properties inside the polymer weld should be taken into account.
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Computational modelling of fatigue crack propagation path in gears
Ševčík, Martin ; Vrbka, M. ; Hutař, Pavel ; Náhlík, Luboš
The paper deals with estimation of fatigue crack behavior for crack propagation from the tooth root. The conditions of linear elastic fracture mechanics are considered. The extension of LEFM – two-parameter LEFM is used for crack path estimation. The effect of the rim thickness on the path of fatigue crack was studied and procedure for more accurate description of the fatigue crack propagation at the gear rim is proposed in the work. Modified maximal tangential stress (MTS) criterion was used for an estimation of the fatigue crack path in the gear rim. Good agreement with experimental results was obtained. More accurate two-parameter description of the stress field around the crack tip can explain the discrepancies between experimental results and previous numerical calculations based on classical one parameter LEFM.
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