Czasopismo Techniczne z. 20. Mechanika z. 4-M

Czasopismo Techniczne z. 20. Mechanika z. 4-M

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New models of fracture in solids at meso- and nanoscales

Wnuk, Michael P.
Article
2010
Novel properties of the present cohesive crack models provide a better insight and an effective tool to explain multiscale nature of fracture process and the associated transitions from macroto meso- and nano-levels of material response to deformation and fracture. Fracture testing of materials with cementitious bonding such as concrete and certain types of ceramics demonstrates that fractal cracks are commonly observed. In the limit of vanishing fracture quantum and/or reduced degree of fractality the quantized cohesive model of a fractal crack, as presented here, reduces to the well-known classic models of Dugdale–Barenblatt or to the linear elastic fracture mechanics or the quantized fracture mechanics theories. Therefore, the basic concepts of linear elastic fracture mechanics, quantized fracture mechanics and fractal geometry are all incorporated into the present theory.

Cyclic steady states of a thick-walled reactor with stress concentrators

Widłak, Grzegorz, Zieliński, Andrzej P.
Article
2010
The paper deals with elastic-plastic stress states in vicinity of a radial cross-bore in a thick-walled reactor loaded by variable internal pressure and a temperature gradient. In the description of material, the linear Prager model of hardening has been applied. The mechanism of development of reverse plastification in each load cycle has been observed. The termal effect is presented on an example of the steady stress states. The transient states (starting and closing work periods of the reactor) have been investigated in the PhD thesis of the first author.

Temperatura empiryczna, czarna, barwowa, korelacyjna i pirometryczna

Wesołowski, Zbigniew
Article
2010
W technice bardzo często obserwowane obiekty są zbyt gorące albo zbyt odległe, by je mierzyć zwykłym termometrem. Przykładami są spoina, piec martenowski, pożar budynku. O mówiono podstawy mierzenia stopnia nagrzania takich ciał. O mówiono temperaturę empiryczną oraz temperatury przeliczeniowe: czarną, barwową, korelacyjną i pirometryczną. Uwypuklono specyficzne cechy każdej z nich.

Hybrid computational systems in structural mechanics

Waszczyszyn, Zenon, Pabisek, Ewa, Kaliszuk, Joanna
Article
2010
The first problem discussed in the paper is related to the reliability of structures. The simulation of the ultimate load of a steel girder is analized by means of a hybrid computational system FEM & ANN & p-EMP. The system consists of three components, with a low fusion grade. FEM is applied for ‘off line’ computing of the patterns for ANN training and testing. The trained AN is then used for very fast generation of MC trials for the hybrid Monte Carlo method (HMC). The second problem corresponds to the identification of a neural material model (NMM) in elasto-plastic plane stress problems. The autoprogressive method (APM) was applied in a formulated hybrid system FEM/NMM/p-EMP with a very high fusion grade of components. The ‘on line’ interaction of all the components is applied at each load incremental step. In the third part of the paper the standing seminar on the application of ANN s in civil engineering, inspired by the ideas of the famous Professor Życzkowski’s Seminar on applied mechanics, is briefly described.

Decohesive carrying capacity of strongly curved I-beam

Szuwalski, Krzysztof
Article
2010
In the paper certain mechanism of ending of process of elastic-plastic deformations forvperfectly elastic-plastic, strongly curved I-beam is discussed. It is connected with separationvof one of flanges from a web, due to infinite value of radial strain in the web. According to Szuwalski, Życzkowski [1] the corresponding value of external loading describes decohesive carrying capacity of the I-beam. T he domain of validity for obtained solutions is defined.

Discontinuous plasticity at extremely low temperatures

Skoczeń, Błażej
Article
2010
Evolution of scientific instruments based on the principle of superconductivity generates ever increasing interest in development and mathematical description of materials suitable for extremely low temperatures. Fcc metals and alloys are frequently used in cryogenic applications, nearly down to the temperature of absolute zero, because of their excellent physical and mechanical properties including ductility. Many of these materials undergo at low temperatures three essentially different dissipative phenomena: discontinuous plastic flow (serrated yielding), plastic strain induced transformation from the parent phase (γ) to the secondary phase (α’) as well as evolution of micro-damage. A ll three phenomena lead to irreversible degradation of lattice and accelerate the process of material failure. Discontinuous yielding belongs to the class of dissipative phenomena often termed plastic flow instabilities. It is characteristic both of low and high stacking fault energy materials loaded beyond the yield point at very low temperatures. Serrated yielding represents oscillatory mode of deformation and reflects discontinuous (in terms of dϭ/dε) nature of plastic flow. It occurs below threshold temperature (T1 or T0) that represents transition from screw to edge dislocations mode. In the present paper a physically based constitutive model of discontinuous plastic flow is presented and its most important features when compared to classical plasticity are highlighted. T he results of low temperature experiments are illustrated and discussed.

Energia powierzchniowa, dyssypacja i efekty skali w modelowaniu mikrostruktur martenytycznych

Petryk, Henryk, Stupkiewicz, Stanisław
Article
2010
W niniejszym artykule przedstawiono energetyczne podejście do wieloskalowego modelowania ewolucji mikrostruktur martenzytycznych w stopach z pamięcią kształtu. Energia swobodna Helmholtza i energia dyssypowana w układzie reprezentowane są przez sumy członów odpowiadających energii objętościowej oraz energii powierzchniowej na granicach mikro-strukturalnych pomiędzy poszczególnymi wariantami martenzytu, fazami lub ziarnami. Ewolucja mikrostruktury jest wyznaczana drogą przyrostowej minimalizacji całkowitej energii dostarczanej do rozpatrywanego układu w procesie makroskopowo quasi-statycznym i izotermicznym. Ogólną procedurę zastosowano do numerycznych symulacji powstawania i ewolucji warstwowych struktur martenzytycznych indukowanych naprężeniowo w stopach z pamięcią kształtu. W energii powierzchniowej uwzględniono energię mikroodkształceń sprężystych w otoczeniu granic mikrostrukturalnych, wyznaczoną przy użyciu metody elementów skończonych. Policzone przykłady opisują ewolucję mikrostruktury martenzytycznej w formie laminatu trzeciego rzędu w stopie CuAlNi dla przemiany 1 1 β→γ′ oraz jej zależność od sposobu uwzględnienia dyssypacji energii powierzchniowej.

Searching of stable configurations of nanostructures using computational intelligence methods

Mrozek, Adam, Kuś, Wacław, Burczyński, Tadeusz
Article
2010
This paper deals with computational intelligence methods: evolutionary algorithms, artificial immune systems and the particle swarm optimization applied to the process of minimization of the potential energy of small nanostructures, such as atomic clusters. These algorithms simulate biological processes of the natural environment and organisms such as the theory of evolution and the biological immune systems. Mentioned approaches, generally, do not need any information about the gradient of the fitness function and give a strong probability of finding the global optimum. The main drawback of these methods is the long time of computations.

Optimal design of thin-valled columns for buckling under combined loadings controlled by displacements

Krużelecki, Jacek, Stawiarski, Adam
Article
2010
In this paper the problem of the optimal design of thin-walled tubular columns under axial compression and torsion controlled by displacements is investigated. A radius of cross-sectional circular profile varying along the axis of the shell-column as well as a wall thickness, which lead to the maximal displacements caused by loadings before the structure buckles are sought. Both global (buckling of a column) and local (wall buckling of a shell) stability of a structure are taken into account. The geometry of the structure is approximated by the convex Bézier polynomial. The results are obtained using the simulated annealing method.

Some exaples on the significance of the notions combined loadings and non-homogeneity in the mechanics of solids and structures

Irschik, Hans
Article
2010
In the following presentation, at first we shortly report about the visits and the fruitful scientific advice, which the late Professor Michał Życzkowski was so kind to spend to the Mechatronics group at the Johannes Kepler University of Linz (JK U Linz) in Austria. Afterwards, we review some own contributions at the Institute of Technical Mechanics of the Mechatronics group in Linz, which were motivated by the research thoughts of Professor Życzkowski. Particularly, we emphasize the usefulness of the notion of Combined Loadings, which we have learned from Professor Życzkowski. Professor Życzkowski introduced this extremely fruitful classification scheme in his famous book on Combined Loadings in the Theory of Plasticity [1], where he distinguished between an analysis at the point level, at the surface level and at the level of the body as a whole. Consequences that have followed from this classification for the scientific strategy of our group concerning elastoplastic vibrations and vibrations of smart (piezoelectric) structures are shortly sketched. In the framework of a pull-out stability problem, nn interesting aspect noted in the celebrated article on the Stability of Bars and Bar Structures [17] by Professor Życzkowski is also addressed. As a whole, we demonstrate how Professor Zyczkowski’s classification scheme serves for us as a highly powerful guide for choosing, explaining and justifying new directions of research in the Mechanics of solids and structures.