Acta Mechanica Slovaca, 2010 (vol. 14), issue 4
On Necessity and Possibility to Fully Exploitation of the Entire Information Inherent in Structural Analysis Data
Karl-Hans Laermann
Acta Mechanica Slovaca 2010, 14(4):6-15 | DOI: 10.2478/v10147-011-0029-5 
The necessity of condition-monitoring and supervising of structures will be justified under aspects of reliability, durability and safety as well as with regard to economical reasons. The achievements in measurement techniques enable the evolution of efficient monitoring systems. The prerequisite will be pointed out, to conceive such systems in close co-ordination with the mathematical modelling of the structure. This is inalienable with concern to system identification as generally the control-parameters cannot be measured directly. They are to exploit on the basis of the mathematical model and the measurable structural response symptoms like displacements...
Analysis of Thermo-Piezoelectricity Problems by Meshless Method
Jan Sládek, Vladimír Sládek, Peter Staňák
Acta Mechanica Slovaca 2010, 14(4):16-27 | DOI: 10.2478/v10147-011-0030-z
In this paper meshless method based on the local Petrov-Galerkin approach is pesented for the solution of boundary value problems for coupled thermo-electro-mechanical fields. Transient dynamic governing equations are considered in analysis of the problems. Material properties of piezoelectric materials are influenced by a thermal field. It is leading to an induced nonhomogeneity and the governing equations are more complicated compared to a homogeneous counterpart. Two-dimensional analyzed domain is divided into small circular subdomains surrounding nodes that are randomly spread over the whole domain. A unit step function is used as the test functions...
Some Possibilities of Determination of Yield Conditions for Cold Rolled Steel Sheets
Fratišek Šimčák, Vladislav Berinštet, Michaela Štamborská
Acta Mechanica Slovaca 2010, 14(4):28-35 | DOI: 10.2478/v10147-011-0031-y
Rolling of metallic materials results to anisotropy of their mechanical properties during plastic deformation. In the paper are described some possibilities of analytical and experimental determination of conditions for plastic deformation of cold rolled steel sheets. The experimental analysis is realized by biaxial tensile test with application of strain gage and optical methods. The results gained by experimental procedures are compared with yield conditions according to individual theories.
Kinematics of Self-Reconfigurable Robotic System
František Trebuňa, Juraj Smrček, Zdenko Bobovský
Acta Mechanica Slovaca 2010, 14(4):36-41 | DOI: 10.2478/v10147-011-0032-x
Theory of mechanisms with variable structure in robotic applications self-reconfigurable structures is one of the directions of development of robotics. On our faculty is developed self-reconfigurable modular robotic system capable of rebuilding a structure according to the requirements of the current task. To perform kinematic changes of its structure we needs to have information on where to find the modules and their submodules. Therefore it is necessary to know the mathematical relationship between the positions of its individual parts. Spatial kinematic chains is investigated based on the theory of simultaneous movements, where the position of...
Computational Modeling of the Probability of Destructions in Total Joint Endoprosthesis Ceramic Heads using Weibull's Theory
Přemysl Janíček, Vladimír Fuis, Michal Málek
Acta Mechanica Slovaca 2010, 14(4):42-51 | DOI: 10.2478/v10147-011-0033-9
This report deals with the issue of finding causes of ceramic heads destructions in total joint endoprostheses. It has been identified that the head fractures were caused by improper mutual geometry tolerances in the taper joint between the ceramic head and the metal stem. This fact was revealed by the results of deformation-stress analyses of heads with various geometric imperfections in the taper contact with the stem using FEM. The issue was further elaborated in the sense of determination of probability of head destruction by existing shape macro-deviations of the taper contact surface of the head and stem, such as varying taper ratio and ovality,...
Experimental Stress Analysis of Transducers by Means of PhotoStress Method
Pavel Macura
Acta Mechanica Slovaca 2010, 14(4):52-57 | DOI: 10.2478/v10147-011-0034-8
This article deals with some experimental stress analysis issues by means of the PhotoStress method. The method was used in order to find out directions and magnitudes of the main stresses at specific cells of the pressure transducers. Since the experimental analysis has been carried out on the curved surfaces of the transducers, the photoelastic coatings had to be cast, shaped, glued on and calibrated before the measurement itself. First of all the article shortly describes calibration process of the cast photoelastic coating made of PL 8 material. Then the measurement procedure and results of courses for the main stresses magnitudes and their directions,...
Parametrical Study of Free Vibration and Plastic Collapse of a Clamped Beam
Pavel Élesztős, Ladislav Écsi
Acta Mechanica Slovaca 2010, 14(4):58-63 | DOI: 10.2478/v10147-011-0035-7
In this paper a parametrical study of free vibration and plastic collapse of a clamped beam is presented. In the numerical study the finite element method was used utilising the updated Lagrangian formulation for large deformations/large strains, the Von Mises material model with multilinear isotropic hardening for hypoelastic-plastic materials, the Kelvin-Voight's model for internal damping and the Jaumann's objective rate in the form of the Green-Naghdi's objective rate for co-rotational Cauchy's stress update calculation, in which appropriate rotation tensors were expressed with the Rodrigues' formula. The aim of this study was to numerically determine...
Numeric Analysis of the Eigenfrequencies of the Ductile Cast Iron with the Spheroidal Shape of Graphite
Ján Vavro, Ján Vavro, jr., Marián Handrik
Acta Mechanica Slovaca 2010, 14(4):64-73 | DOI: 10.2478/v10147-011-0036-6
The given work is focused on the analysis of the eigenfreqencies and natural shapes as well as it is connected with stress distribution in the frequency area referring to the ductile cast iron with the spheroidal shape of graphite. The analysis was made with help of finite element method (FEM) in the software system ADINA.v.8.6.2.
Dynamic Analysis of the Two-Mass System to Imitate Rectilinear Motion of a Snake
Alexander Gmiterko, Ivan Virgala, Martina Vacková
Acta Mechanica Slovaca 2010, 14(4):74-81 | DOI: 10.2478/v10147-011-0037-5
A few previous decades the researchers and the designers started to copy the animal motion to the mechanisms. The principal motivations of the snaky locomotion are the environments where the traditional machines are not applicable due their dimensions or shapes and where the accessories like the wheels or the legs fail. The paper deals with the dynamic analysis of the two-mass system imitating the snake rectilinear motion on the level surface. Within the research there were made various modifications of the system and through the simulation was verified the behavior of the kinematic parameters. Based on the mentioned displacements and the speeds depending...
Further Possibilities of Using Software PhotoStress for Separation of Principal Normal Stresses
František Trebuňa, Ján Jadlovský, Peter Frankovský, Zuzana Bakšiová, Anna Kostelníková
Acta Mechanica Slovaca 2010, 14(4):82-91 | DOI: 10.2478/v10147-011-0038-4
Software PhotoStress, elaborated in our laboratories allows determination of directions and magnitudes of strains or principal normal stresses in loaded photoelastically coated structural elements. It allows accelerating process of measurement and evaluation of deformations or stresses in point, along line or along curve, respectively. In those entities can be determined directions, and magnitudes of differences and separated principal deformations or stresses on the basis of photography of loaded photoelastically coated objects. In the paper is given procedure for of evaluation of separated principal normal stresses by using of separation methods:...
Some Aspects of Probability and Possibility Theories for Numerical Analysis of Uncertain Mechanical Systems
Milan Sága, Vladimír Dekýš, Milan Vaško
Acta Mechanica Slovaca 2010, 14(4):92-101 | DOI: 10.2478/v10147-011-0039-3
Our paper presents chosen traditional (based on probability theory) and non-traditional (based on possibility theory) computational tools for analysis of the material, geometric or loading uncertainties in mechanical structures. Uncertainties are introduced as bounded possible values - intervals or as fuzzy sets, assuming possibility theory and as random parameters in the case of the probability theory. The main goal is to propose numerical algorithms for interval modal and spectral FE computations suggested by authors and their additional implementation into fuzzy analysis and Monte Carlo method.
Adaptable Mechatronic Locomotion System
Alexander Gmiterko, Michal Kelemen, Tatiana Kelemenová, Ľubica Miková
Acta Mechanica Slovaca 2010, 14(4):102-109 | DOI: 10.2478/v10147-011-0040-x
Wheeled in-pipe locomotion is very favourite principle of locomotion used inside pipe. However, there are several problems in these systems like slipping or deadlocking on inner pipe wall. The construction of the system provides adaptation of the wheels position i.e. adaptation of the normal force of the wheels against to the inner pipe wall. This property is important, because of geometric deviations on inner pipe wall. Information about the actual normal force of wheels against the inner pipe wall is used for regulation of their value. When normal force is too small then slipping occurs, but if normal force is too large then deadlocking occurs. A...