National Repository of Grey Literature 13 records found  1 - 10next  jump to record: Search took 0.00 seconds. 
Single lever control system of piston engine with propeller
Gröger, Roman ; Cäsar, Tomáš (referee) ; Šplíchal, Miroslav (advisor)
This bachelor thesis deals with the description of the work of aircraft piston power plants and single-lever control systems. The first part describes the characteristics of piston engines and their indicators. The second part describes the work of piston engines with variable-pitch propeller. The third and fourth part deals with single-lever control systems of piston power plant, their comparison and possible problems of their control.
Thermodynamics of Dislocation Pattern Formation at the Mesoscale
Gröger, Roman
We introduce a mesoscopic framework that is capable of simulating the evolution of dislocation networks and, at the same time, spatial variations of the stress, strain and displacement fields throughout the body. Within this model, dislocations are viewed as sources of incompatibility of strains. The free energy of a deformed solid is represented by the elastic strain energy that can be augmented by gradient terms to reproduce dispersive nature of acoustic phonons and thus set the length scale of the problem. The elastic strain field that is due to a known dislocation network is obtained by minimizing the strain energy subject to the corresponding field of incompatibility constraints. These stresses impose Peach-Koehler forces on all dislocations and thus drive the evolution of the dislocation network.
The numerical analysis of interactions between twins and precipitates in magnesium alloys
Bogdan, Miloš ; Gröger, Roman (referee) ; Šiška, Filip (advisor)
Hlavním cílem této práce je analýza napěťových polí, indukovaných dvojčatěním ovlivněných přítomností precipitátu před čelem dvojčete. Zvolený případ popisuje tahové dvojče {1012} 101 1 s lamelarními precipitáty v hořčíkové slitině AZ31. Systém je modelován metodou konečnýh prvků jako 2D elastická eliptická inkluze, se dvěmi elastickými precipitáty tyčovitého tvaru, nacházející se před čelem elipsy obklopené plastickou matricí modelovanou pomocí krystalové plasticity. Analýza dvojčat a precipitátů s různou tlouštkou ukazje inhibující účinek precipitátů na růst tloušťky dvojčat. Velikost tohoto účinku se mění s tloušťkou dvojčete v důsledku komplexní interakce mezi dvojčetem precipitátem a indukovanou plastickou zónou.
Calculations of fract. param. of general stress concentrators:III.Analysis of the stress field around a tip of a sharp V-notch
Náhlík, Luboš ; Gröger, Roman
In the article is under assumptions of linear elastic fracture mechanics analyzed problem of the sharp V-notch with its tip on the bi-material interface, as a example of general stress concentrator. The procedure for the determination of stress singularity exponents is performed for general cases, when this exponent lies within the interval (0,1). The procedure for an estimation of the general stress intensity factor for considered configuration is shown too. Here is suggested method which consider both types of stress singularities which exist in this case.
Calculations of fracture parameters of a general stress concentrators: III. Analysis of the stress field around a tip of a sharp
Náhlík, Luboš ; Gröger, Roman
In the article is under assumptions of linear elastic fracture mechanics analyzed problem of the sharp V-notch with its tip on the bi-material interface, as a example of general stress concentrator. The procedure for the determination of stress singularity exponents is performed for general cases, when this exponent lies within the interval (0,1). The procedure for an estimation of the general stress intensity factor for considered configuration is shown too. Here is suggested method which consider both types of stress singularities which exist in this case.
Determination of T stress for arbitrary oriented crack terminating at interface between two dissimilar materials
Gröger, Roman
The most important factors describing the fracture-mechanics behavior of layered structures are the generalized stress intensity factor and also T stress describing the amplitude of the stress field independent on the radial distance from the crack tip.. Direct methods of the calculation of such parameters are well known and their accuracy is critically assessed by the experimental measurements. The present work proposes an alternative method of determining of the elastic T stress based on the validity of the reciprocal work theorem using the integration of the strain energy along a circular path surrounding the crack tip. The results obtained from a model of a crack terminating at interface between two dissimilar elastic materials are compared with the usually used direct approach. It is shown that such this term is not negligible and generally need to be taken into account in the considerations on the stability of layered materials.
Theoretical background for determining the fracture-mechanics parameters using the Boundary Element Method
Gröger, Roman
Boundary Element Method is a powerful tool for certain class of Solid Mechanics problems, where the fundamental solution of the governing differential equation is known. This article briefly outlines the theoretical background of BEM for plane problems as well as integral identities for calculation of internal stresses and displacements. Chapter 2 introduces the most useful contour integrals for calculation of fracture parameters in two-parameter linear elastic fracture mechanics. These coefficients are solved using the stress and strain tensor field calculated using BEM. All the proposed and discussed approaches are compared and the differences between FEM and BEM are discussed.
Application of contour integrals to assessment of notch stability in linear elasticity
Gröger, Roman ; Knésl, Zdeněk
The article yields a teoretical background of a well- sophisticated numerical method for calculation of GSIF and T stress, especially for case when the integration across the nonhomogeneous material interface is unavoidable. The main advantage of the integral approach over the well-known direct methods is its accuracy induced by monotonous convergence of the solution. This work contributes to more accurate description of the instability state of V-notches in composite structures.
Integral methods for the determination of fracture characteristics of general stress concentrators
Gröger, Roman
The integral appoaches for calculation of generalized stress intensity factors (GSIF) are presented. Integral identities are derived using the Betti reciprocal theorem as a superposition of two independent solutions satisfying the sam boundary conditions. The complementary solution for computation of GSIF is assembled using the negative eigenvalues lambda. This algorithm yields a set of integral identities that allow to estimate GSIF separately for mode I and II. A quantitative comparsion of the integral approach with recently used extrapolation method is proposed in conclusion.
Calculation of fracture parameters for the cracked bodies strengthened by circular patches
Gröger, Roman
The present article yields a quantitative characterization of the influence of geometry and material properties on the values of fracture parameters. Both the cracked sheets with single and double circular patches are used for the analysis. The desired value of elastic T stress is obtained using the conservation M integral resulting from the Eshelby integral concept. For the SIF calculation, the indirect method of J integral is used and the general concept for the SIF separation in case of a mixed mode of loading is discussed here. The reduction effect is specified by the ratios of SIF and T stress. The method of stiffening the region surrounding the crack tip can be used as an alternative method of the lifetime prolongation, but cannot be used in all cases. Sometimes the usual method of the crack tip singularity cancellation is the only one to repair the structure.

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