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Search Results: 1 - 10 of 3142 matches for " Applied mechanics "
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Fatigue aspects of an evaluation of the operational safety of components working in creep conditions
J. Okrajni
Journal of Achievements in Materials and Manufacturing Engineering , 2011,
Abstract: Purpose: The main purpose is the method of the description of the thermo-mechanical fatigue process of power plant components working under mechanical and thermal loading. The work focuses on the chosen component strain-stress characteristics and their strength. The paper discusses the issue of modelling the heating and cooling processes of components in a power plants in the start-up and shut-down conditions of a boiler.Design/methodology/approach: The FEM modelling has been used to describe the local stress-strain behaviour of the chosen component.Findings: The calculations of stress distribution on the chosen component surface show that the internal pressure induces considerably smaller values of stresses and strains in comparison with the same stresses specified for thermal loads. However, it should be noted that the impact of temperature gradients and thermal stresses is usually short-lived, therefore, its influence on creep processes is less significant in comparison to pressure load. Material fatigue is mainly the effect of thermal stresses. Thus, thermal impacts are responsible for cracks initiation and growth in areas of the greatest intensity of damage accumulation.Research limitations/implications: The presented analysis is the part of the complex investigation method which main purpose is increasing the accuracy of the TMF process description and thermo-mechanical life assessment. The possibility of applying the fatigue durability criteria currently assumed in standards still requires justification and confirmation in laboratory and industrial conditions to be closer to the real components behaviour. In such situation the industrial investigations curried out in the work give the model approach and data for the comparison the real behaviour with the predictions.Practical implications: The method of stress-strain behaviour analysis used in the paper could be useful in the practical cases when the real components mechanical behaviour would be analysed.Originality/value: The main value of this paper is the own method of the mechanical behaviour analysis of the power plant component. This method includes the temperature fields analysis taking into account the boundary conditions based on the operation parameter data and the thermoplastic material model. The material stress-strain behaviour has been treated as the local phenomenon, that could be modelled by FEM.
An analysis of applied mechanics contest for senior high school students in Taiwan
Nelson Cheng-Chih CHEN,Ching-Hao CHEN,Ming-chun LIN
Asia-Pacific Forum on Science Learning and Teaching , 2008,
Abstract: The applied mechanics education contest hosted by STAM (Society of Theoretical Applied Mechanics) has been held in Taiwan for several years. The contest pattern has been changed from a simple written test to an experiment-oriented test after the NSTM (National Science and Technology Museum) proceeded to hold the competition in 2005. The major change of the contest is to merge theory with a practical experiment. The NSTM set up well-designed video shows and materials packs for hands-on experiments at the contests. Visiting related mechanics exhibits at NSTM was highly recommended by the contestants and teachers. Statistical analyses of the contest scores over the past four years shows no significant correlation between the medals and the areas where the contestants are from, and there was no significant difference among the contestants’ final scores for different areas. Since 2004, the outstanding students at the competition were selected to attend the annual cross-strait mechanics field academic exchanges, and this academic exchange will continue to help extend the influence of mechanics education in Taiwan and China.
Stres-strain characteristics under mechanical and thermal loading
J. Okrajni,A. Marek,G. Junak
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: The main problem addressed in the paper is the description of a deformation process under theconditions of mechanical and thermal interactions.Design/methodology/approach: The mathematical modelling has been used to describe the stress-strainbehaviour of materials. The method of fatigue testing has been adopted to determine experimentally stress-straincharacteristics. The method based on the long term own experience in thermo-mechanical investigations andnew European Code-of-Practice for Thermo-Mechanical Fatigue Testing.Findings: An appropriate model description has been developed. Fatigue examinations of the P91 steel that isused in power industry, were carried out. The validation of the model has been performed. So far, experimentalverification of the usefulness of the model description to determine the stress-strain characteristics’ course fora selected value of the phase shift angle between the temperature and total strain cycles has been made. It hasbeen found that the proposed model reflects the deformation process nature very well in variable temperature,strain and stress conditions. Hence, a conclusion seems to be justified that the approach presented in the papercould constitute the right basis for appropriate constitutive equations, which depict the material behaviour underthermo-mechanical conditions.Research limitations/implications: The developed description should be useful in problems of fatigue behaviourpredictions of materials under different mechanical and thermal loadings in industry practical applications and inresearch problems connected for instance with fatigue life criteria description and validation.Originality/value: The new material characteristics have been shown in the work and the own new method ofthe material fatigue behaviour prediction. The work is addressed to researchers interested in problems of materialtesting and material behaviour prediction under different loadings that we can meet in the operation practice.
Description of the deformation process under thermo-mechanical fatigue
J. Okrajni,A. Marek,G. Junak
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: The main problem addressed in the paper is the description of a deformation process under the conditions of mechanical and thermal interactions.Design/methodology/approach: The mathematical modelling has been used to describe the stress-strain behaviour of materials. The method of fatigue testing has been adopted to determine experimentally stress-strain characteristics. The method based on the long term own experience in thermo-mechanical investigations and new European Code-of-Practice for Thermo-Mechanical Fatigue Testing.Findings: An appropriate model description has been developed. Fatigue examinations of the P91 steel that is used in power industry, were carried out. The validation of the model has been performed. So far, experimental verification of the usefulness of the model description to determine the stress-strain characteristics’ course for a selected value of the phase shift angle between the temperature and total strain cycles has been made. It has been found that the proposed model reflects the deformation process nature very well in variable temperature, strain and stress conditions. Hence, a conclusion seems to be justified that the approach presented in the paper could constitute the right basis for appropriate constitutive equations, which depict the material behaviour under thermo-mechanical conditions.Research limitations/implications: The developed description should be useful in problems of fatigue behaviour predictions of materials under different mechanical and thermal loadings in industry practical applications and in research problems connected for instance with fatigue life criteria description and validation.Originality/value: The new material characteristics have been shown in the work and the own new method of the material fatigue behaviour prediction. The work is addressed to researchers interested in problems of material testing and material behaviour prediction under different loadings that we can meet in the operation practice.
Dynamical flexibility of rod and beam systems in transportation
S. ?ó?kiewski
Journal of Achievements in Materials and Manufacturing Engineering , 2008,
Abstract: Purpose: Purpose of this paper is to present a mathematical model of rod and beam systems in transportation. The mathematical model is presented in the form of dynamical flexibility of systems. Systems are considered as flexible rotating rods and flexible rotating beams. In solution there was took into account the interaction between the main motion and local vibrations of elements.Design/methodology/approach: The dynamical flexibility was derived by the approximate method, the Galerkin’s method. The example dynamical characteristics were presented in form of attenuation-frequency characteristics. The dynamical flexibility was derived on the basis of known equations of motion derived in other publications.Findings: There can be observed so called the transportation effect. This effect consist in that when analyzed system rotates with some angular velocity in the characteristic of dynamical flexibility we can notice additional poles and after increasing angular velocity it is noticeable that created modes are symmetrically propagated from the original mode. It is also palpable fact, instead of the original mode there is created zero.Research limitations/implications: Analyzed systems are simple linear type beams and rods in rotational motion. Motion was restricted to plane motion. Future research ought to consider complex systems, damped models and also nonlinearity.Practical implications: Practical implications of derived mathematical models of beam and rod systems both the free-free ones and fixed ones is a possibility of derivation of the stability zones of analyzed systems and derivation of eigenfrequencies and zeros in the way of changing the value of angular velocity.Originality/value: Presented models apply to rotating flexible rod and beam systems with taking into consideration the transportation effect. It is a new approach of analyzing rod and beam systems and can be put to use in modelling and analyzing machines and mechanisms in rotational transportation.
Life and operational safety of power systems and chemical plants
J. Okrajni
Journal of Achievements in Materials and Manufacturing Engineering , 2010,
Abstract: Purpose: The problem addressed in the paper is the description of an effort and durability of components under the conditions of mechanical and thermal interactions. The problems of proper material testing methods have been shown as the important part of the components life assessment methodology.Design/methodology/approach: The FEM modelling has been used to determine the stress and strain fields in the components and to describe their behaviour under mechanical and thermal loading.Findings: An appropriate models description has been developed. So far, experimental verification of the usefulness of the model description to determine the stress and strain patterns in particular object and for chosen operation conditions has been made.Research limitations/implications: The developed description should be useful in problems of behaviour predictions of high temperature components and their durability assessment under different mechanical and thermal loadings in industry practical applications.Originality/value: The method, which more precise description of power industry components behaviour makes possible have been shown in the work. The work is addressed to researchers interested in problems of component behaviour prediction under different loadings that we can meet in the operation practice and to power industry engineering maintenance staff.
Dynamical flexibilities of mechanical rotational systems
S. ?ó?kiewski
Journal of Achievements in Materials and Manufacturing Engineering , 2008,
Abstract: Purpose: of this work is to present dynamical flexibilities of rotational beams and rods systems. The results ofmathematical calculations were presented in the form of dynamical flexibility of analyzed systems. In final solutionthere were took into consideration the interactions between the major motions and local vibrations of subsystems.Design/methodology/approach: The dynamical flexibilities were derived by the Galerkin’s method. The dynamicalflexibilities for example numerical cases were presented onto charts of attenuation-frequency characteristics. Themathematical models were derived on the basis of known equations of motion derived in previous thesis’s.Findings: After analysis of characteristics we can observe the transportation effect. We can notice additional poleson the characteristic of dynamical flexibility characteristics and after increasing angular velocity created modessymmetrically propagate from the origin mode and instead of the original mode there is created a zero’s amplitude.Research limitations/implications: Analyzed systems are beams and rods in rotational motion. Motion waslimited to plane motion. Future works will be connected with consideration of complex systems.Practical implications: of derived dynamical flexibilities of free-free and fixed beams and rods systems is apossibility of derivation of the stability zones of analyzed systems and derivation of eigenfrequencies and zerosin the function of angular velocity of work motion.Originality/value: Models analyzed in this thesis apply to rotating rod and beam systems with taking intoconsideration the transportation effect. This new approach of analyzing rod and beam systems can be put to usein modelling, analyzing and designing machines and mechanisms with rotational elements.
Steam pipelines' effort and durability
J. Okrajni,K. Mutwil,M. Cie?la
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: The main problem addressed in the paper is the description of an effort and durability of steam pipelines under the conditions of mechanical and thermal interactions.Design/methodology/approach: The FEM modelling has been used to determine the stress and strain fields in the pipelines and to describe their behaviour under mechanical and thermal loading.Findings: An appropriate model description has been developed. So far, experimental verification of the usefulness of the model description to determine the stress and strain patterns in particular object and for chosen operation conditions has been made. The analysis made has shown that the most probable cause of cracks occurrence on the analyzed chosen pipeline’ inner surfaces are thermal deformations and constraints of their dislocations.Research limitations/implications: The developed description should be useful in problems of behaviour predictions of high temperature components and their durability assessment under different mechanical and thermal loadings in industry practical applications.Originality/value: The method, which more precise description of power industry components behaviour makes possible have been shown in the work. The work is addressed to researchers interested in problems of component behaviour prediction under different loadings that we can meet in the operation practice and to power industry engineering maintenance staff.
Modelling, synthesis, modification, sensitivity and analysis of mechanic and mechatronic systems
A. Buchacz
Journal of Achievements in Materials and Manufacturing Engineering , 2007,
Abstract: Purpose: The main purpose of this thesis is the research of the authors scientific problematic which were presented during the AMME and CAM3S conferences.Design/methodology/approach: The main approach to the problem is to present the variety of the conferences and on this background – the abilities of the propositions for the potential participants. According to the author of this article these were the topics concerning - modelling, synthesis, design, examining the sensitivity, modifications of discrete, continuous, discrete continuous mechatronic systems and machatronic active or passive and also taking into consideration the transportation.Findings: The flexibility impact of the manipulators chains in fix position with the transportation was examined. The problem of the synthesis and examining the sensitivity of continuous and discrete continuous systems with the usage of method of examining this problem with discrete models was formulated and solved. The problem: of structural modification of different type of systems was formulated and solved; of active discrete structures. The methods of synthesis according to selected class of dynamical characteristic in order to generate the “new” structures – physical realizations in a shape of models of mechatronic systems were given.Research limitations/implications: The various linear mechanical and mechatronic systems were modelled, synthesised, design and analysed.Practical implications: Obtained results can be used as a field of improving and developing the modelling methods as far as design and examining the various class of vibrating mechanical and mechatronic systems are concerned. Mentioned results can be also useful for the engineers which are working with this or similar problems.Originality/value: New modelling methods, synthesis, examination of sensitivity and modifications of selectaed class of mechanic and mechatronic systems represented by graphs and structural numbers were presented.
First Theoretical Constructions to the Fluid Mechanics Problem of the Discharge  [PDF]
Sylvio R. Bistafa
Advances in Historical Studies (AHS) , 2015, DOI: 10.4236/ahs.2015.43015
Abstract: After the publication of Hydrodynamics by Daniel Bernoulli in 1738, there was a fierce competition for priority with his father, Johann Bernoulli, and controversies with Jean le Rond D’Alembert, in which Leonard Euler seemed to have tacitly accepted the role of presiding over the disputes. These disputes were aroused by the almost simultaneous publications of Hydraulics by J. Bernoulli in 1743 and of Traité de l’équilibre et du mouvement des fluides by D’Alembert in 1744. It would be shown that despite the fact that the Bernoullis and D’Alembert used their own principles and approaches to the fluid mechanics problem of discharge, they essentially reached the same end. Nonetheless, it was Euler who brought the fluid mechanics problem of discharge to a new and definitive level with two publications. In these publications, for the first time, the pressure force and the friction force appeared explicitly in the formulations. However, the friction force was built under the wrong assumption that, as for the case of solid friction, the fluid friction force was proportional to the pressure. Finally, Lagrange’s memoir on the theory of fluid motion of 1781 is presented as a sequel to these first theoretical constructions.
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