Pavol Lengvarský

An Investigation of the Temperature Influence on a Shift of Natural Frequencies Using Digital Image Correlation

The contribution describes an original optical measuring technique serving for the investigation of temperature influence on the shift of investigated objects natural frequencies. The mentioned method uses a modified high-speed digital image correlation system with original program Modan 3D created in Matlab, by which it is possible to non-contactly determine the natural frequencies using complex mode indicator function (CMIF) or normal mode indicator function (NMIF), the mode shapes as well as the damping ratio. Influence of the temperature on the shift of natural frequencies was analyzed at the planar steel specimen of circular shape with three holes. To the excitation a modal hammer was used. The specimen heating was realized by a hot-air gun, whereby the influence of the elevated temperature on the shift of natural frequencies was investigated by three temperatures distinguishing the room temperature 50° C, 75° C and 100° C.

The Use of Nonlocal Theory for Bending Vibrations of Single-Walled Carbon Nanotubes

In the paper are investigated the eigenfrequencies of single-walled carbon nanotubes (SWCNTs) by the analytical method based on nonlocal theory of beam bending. A continuum approach is applied for eigenfrequency computation of SWCNTs with four types of beam end conditions: clamped-free (C-F), simply-simply supported (S-S), clamped-simply supported (C-S) and clamped-clamped (C-C).

Buckling Analysis of Hetero-Junction Carbon Nanotubes

Abstract The buckling analysis of carbon nanotubes without and with hetero-junctions is described in this paper. The buckling behaviour was investigated by the finite element method and the carbon nanotubes were modelled as space frame structures. The results showed that the critical buckling force depends on the dimensions of carbon nanotubes. The critical buckling forces of hetero-junction carbon nanotubes are in range between critical buckling forces of carbon nanotubes of both used diameters with the same chiralities without hetero-junction.

The Use of Optical Methods in the Analysis of the Areas with Stress Concentration

Abstract Anchoring parts of technical systems are often damaged due to the heavy forces acting on these systems during their operation. For that reason, various modifications are suggested and created on the anchoring screws, which should help to reduce the mechanical stress values in a place of the first load-bearing thread of a female screw. For the determination of stress fields on the surface of a plane model of a threaded joint, two non-contact optical methods were used – conventional transmission photoelasticimetry and modern digital image correlation.

Application of finite element method for analysis of nanostructures

Abstract The paper deals with application of the finite element method in modelling and simulation of nanostructures. The finite element model is based on beam elements with stiffness properties gained from the quantum mechanics and nonlinear spring elements with force-displacement relation are gained from Morse potential. Several basic mechanical properties of structures are computed by homogenization of nanostructure, e.g. Youngs modulus, Poissons ratio. The problems connecting with geometrical parameters of nanostructures are considered and their influences to resulting homogenized quantities are mentioned.

Possibility of Using of Tensometry in Deformation Analysis in Areas With Sudden Change of Geometry

In the process of design of machines and equipment high attention has to be given to structural notches, defects of materials and surface quality, because they have high impact to their fatigue strength. In the paper is presented proposal of methodology concerning deformation analysis near stress concentrators by using strain gages. The experimental measurement was realized on bended U-shape specimen with notches. The results gained by experimental measurements were verified by numerical modelling by the finite element method.

Using of Air Natural Convection for Cooling of Casks with Spent Nuclear Fuel in Dry Storage System

The paper is devoted to the description of project of storage system for the spent nuclear fuel. The proposed dry storage system is based on the natural convection of air so no additional fans are needed for the cooling. In the paper basic parameters of the storage as well as some preliminary computations verifying its concept are described.

Influence of different random pattern creation forms on the results of experimental modal analysis performed by high-speed digital image correlation

Abstract In this contribution an influence of random contrast patterns creation on the quality of the obtained results of experimental modal analysis performed by high-speed digital image correlation is described. Three common forms of random pattern creation were investigated. While the first form was presented by the black speckles printed on white matt vinyl foil and bonded on the sample surface, in the second and the third case, respectively, the black speckles were sprayed on white sprayed sample surface or on paint white one. For the purposes of modal parameters estimation in the form of natural frequencies, mode shapes and damping ratios the program called Modan3D, developed in the authors department, was used. The results obtained by Modan3D were compared with the results achieved by system Pulse specialized for vibration analysis.