Rozprawy doktorskie: „Shakedown”

1

Zhang, Jin. "Shakedown of porous materials". Thesis, Lille 1, 2018. http://www.theses.fr/2018LIL1I044/document.

Streszczenie:

Cette thèse est consacrée à la détermination des états limites de l'adaptation des matériaux ductiles poreux sur la base du théorème de Melan et en considérant le modèle de la sphère creuse. Dans un premier temps, nous proposons le critère analytique macroscopique d'adaptation avec la matrice de von Mises sous deux charges particuliers, alterné et pulsé. Le critère analytique dépend des première et seconde invariants des contraintes macroscopiques, du signe du troisième et du coefficient de Poisson. Ensuite, ce critère est étendu aux charges cycliques répétées générales par la construction d'un champ de contraintes résiduelles d'essai plus approprié permettant simultanément des calculs analytiques et l'amélioration du modèle précédent. De plus, il est également utilisé pour les matériaux ductiles poreux avec une matrice de Drucker-Prager.L'idée repose d'abord sur la solution exacte pour le charge purement hydrostatique. Il s'avère que la ruine se produit par fatigue. Ensuite, des champs de contrainte d'essai appropriés sont construits avec des termes supplémentaires pour capter les effets de cisaillement. Le domaine de sécurité, défini par l'intersection du domaine d'adaptationet celui d'analyse limite (la ruine survenant brusquement par formation d'un mécanisme au premier cycle), est entièrement comparé avec des simulations élasto-plastique incrémentales et des calculs directs simplifiés.Enfin, nous fournissons une méthode numérique directe pour prédire le domaine de sécurité de l'adaptation des matériaux poreux soumis à des charges variant de manière indépendante en considérant le chemin critique du domaine de chargement au lieu de l'histoire entière. Le problème de l'adaptation est transformé en un problème d'optimisation de grande taille, qui peut être résolu efficacement par l'optimiseur non-linéaire IPOPT pour donner non seulement le facteur de charge limite, mais aussi le champ de contrainte résiduelle correspondant à l'état d'adaptation
This thesis is devoted to the determination of shakedown limit states of porous ductile materials based on Melan's static theorem by considering the hollow sphere model, analytically and numerically. First of all, we determine the analytical macroscopic shakedown criterion of the considered unit cell with von Mises matrix under alternating and pulsating special loading cases. The proposed macroscopic analytical criterion depends on the first and second macroscopic stresses invariants, the sign of the third one and Poisson's ratio. Then, the procedure is extended to the general cyclically repeated loads by the construction of a more appropriate trial residual stress field allowing analytical computations and the improvement of the previous model simultaneously. Moreover, this approach is applied to porous materials with dilatant Drucker-Prager matrix.The idea relies firstly on the exact solution for the pure hydrostatic loading condition. It turns out that the collapse occurs by fatigue. Next, suitable trial stress fields are built with additional terms to capture the shear effects. The safety domain, defined by the intersection of the shakedown limit domain and the limit analysis domain corresponding to the sudden collapse by development of a mechanism at the first cycle, is fully compared with step-by-step incremental elastic-plastic simulations and simplified direct computations. At last, we provide a direct numerical method to predict the shakedown safety domain of porous materials subjected to multi-varying independent loadings by considering the critical loading path of the load domain instead of the whole history. The shakedown problem is transformed into a large-size optimization problem, which can be solved efficiently by the non-linear optimizer IPOPT to give out not only the limit load factor, but also the corresponding residual stress field for the shakedown state

Style APA, Harvard, Vancouver, ISO itp.

2

Engelhardt, Markus Jochen. "Computational modelling of shakedown". Thesis, University of Leicester, 1999. http://hdl.handle.net/2381/30173.

Pełny tekst źródła

Streszczenie:

The work presented is concerned with the implementation and exploitation of an iterative non-linear programming technique, based on the elastic compensation method, for solving limit load and shakedown problems. Such solutions are required in the design of structures or components subjected to complex combinations of static and cyclic loading, in structural integrity procedures and life cycle assessment. To achieve these aims, a brief review of the problem, the historical development of shakedown theory and recent developments of methods addressing these issues are given in the early chapters. This is followed by the implementation of the above method to generate limit load solutions for elastic-plastic materials subject to the von Mises yield condition. The method was found to be numerically stable and convergence could be guaranteed for upper bound limit load solutions if a number of sufficient convergence criteria are adhered to. These are stated during the provided convergence proofs. Upon studying the behaviour of the method, i.e. quality and sensitivity of solutions, computational effort as well as identifying error sources, this implementation is extended to solve limit load problems for arbitrary yield surfaces. This was found to be possible, but dependent on the nature of the yield surface and limits to the implementation in its present form were identified. The method was then implemented using a different formulation capable of solving limit and, more importantly, shakedown problems for elastic-plastic materials subject to the von Mises yield criterion. A number of benchmark problems were considered, an example of which is the classic Bree problem, which is concerned with shakedown of components subjected to a static mechanical load in combination with thermal transients. The method performed well and was then used to solve novel shakedown problems, such as shakedown states where creep must be considered. Acceptable creep behaviour for a given shakedown state could also be calculated using minor additions. The final issue considered was cyclic creep solutions. Rapid cycle creep solutions could be generated as a stress history can be considered, which is of a similar form to shakedown. Finally, conclusions were drawn and remaining issues discussed.

Style APA, Harvard, Vancouver, ISO itp.

3

Faria, P. de D. "Shakedown analysis in geotechnical engineering". Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636956.

Pełny tekst źródła

Streszczenie:

Many problems in geotechnology are concerned with the response of earth materials to cyclic loads. These loads are either generated by forces of nature such as sea waves, currents, winds, and earthquakes or as a consequence of engineering operations such as blasting, pile driving and rotating machines. For most design purposes related to static loads it is logical to use as a design basis either the elastic range where no plastic deformation occurs or the plastic range, in which large plastic deformation can occur. However, when cyclic loading is involved few design methods are available since a pattern for the response of the body to cyclic loads is not well known. When a body is subjected to cyclic loading some modes of adaptation or non adaptation can occur as a response to the loads such as elastic shakedown, alternating plasticity and ratchetting. Despite its extensive use in structural problems very few applications of the shakedown approach to soil masses can be found in literature. Therefore the present work aims to extend the elastic shakedown concepts to geotechnical problems. Initially the shakedown concepts are introduced, its theorems and their importance for geomechanical problems are highlighted. Later the use of Melan's static shakedown theorem for the present study is shown. Shakedown analyses of plane stress and plane strain problems are presented. In this study the shakedown formulation is based on the concept of a residual stress field obtained by means of a numerical formulation using a visco-plastic algorithm. Two numerical codes linked with a mesh generator were implemented as tools for the treatment of the shakedown problems. Numerical examples and applications are shown to illustrate the usefulness of the present approach.

Style APA, Harvard, Vancouver, ISO itp.

4

Franco, Jose Ricardo Queiroz. "Bounding techniques in shakedown and ratchetting". Thesis, University of Leicester, 1987. http://hdl.handle.net/2381/8237.

Pełny tekst źródła

Streszczenie:

A review of Shakedown and Ratchetting concepts and their extensions is presented in an attempt to recount all the aspects of the problems considered in this research programme. The concept of Stress Concentration Factor was the first to be further investigated, by analysing two representative types of structures operating under severe stress concentration, namely; two-bar structures and cylindrical vessels with variable thickness subjected to cyclic mechanical loads. The material behaviour considered are: elastic-perfectly plastic and isotropic hardening. Such an analytical investigation allowed the assessment of the influence of the Stress Concentration Factor below and above the limit of reversed plasticity. The primary aim of this research was to develop simplified techniques capable of solving thermal loading problems in the presence of steady mechanical loads. A simplified technique was then developed to analyse a tube subjected to a complex thermal loading simulating the fluctuation of level of sodium in Liquid Metal Fast Breeder Reactors (LMFBR). The technique was also able to include a second important aspect of shakedown problems which is cases of multiple mechanical loads. The construction of bi-dimensional Bree type diagrams, from tri-dimensional ones obtained for such cases, allowed an easy assessment of the modes of deformation of the structure. The effects of the temperature on the yield stress were explored. A third aspect of thermal cyclic problems investigated was the experimental verification of the reliability of the extended Upper Bound Theorem proposed in Chapter 2. This was achieved by experimental tests on portal frames at 400°C. Contours representing states of constant of deformation were obtained from the experimental measurements. A fourth aspect of the problem was the development of theoretical technique to estimate the transient plastic deformation in excess of the shakedown limit which allowed the construction of theoretical contours directly comparable with the experimental ones. The fifth and major contribution of this thesis was the development of a general technique for the analysis of axi-symmetric shells based in a displacement formulation for the Finite Element Method. Limit analysis and shakedown problems were reduced to minimization problems by developing a technique to obtain consistent relationship between the displacement field and the plastic strain field. Such a technique, based upon a Galerkin type of approach, consist of minimizing the difference between the two representations of the strain within the element; in terms of nodal displacement and in terms of plastic multipliers. The problem was then solved by Linear Programming. Finally, the conclusions and proposal for future work are presented.

Style APA, Harvard, Vancouver, ISO itp.

5

Kobayashi, Shun-ichi. "Limit and Shakedown Design in Geotechnical Engineering". 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/148311.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

6

Hearle, Adrian Donald. "Deformation, shakedown and fatigue in rolling contact". Thesis, University of Cambridge, 1985. https://www.repository.cam.ac.uk/handle/1810/250858.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

7

Ngo, Ngoc Son Civil &amp Environmental Engineering Faculty of Engineering UNSW. "Limit and shakedown analyses by the p-version fem". Awarded by:University of New South Wales. Civil and Environmental Engineering, 2005. http://handle.unsw.edu.au/1959.4/23463.

Pełny tekst źródła

Streszczenie:

This thesis provides a contribution towards a general procedure for solving robustly and efficiently limit and shakedown analyses of engineering structures within the static approach which has been chosen for its simplicity of implementation. Throughout the thesis, attempts at improving the robustness and efficiency of the computations are presented. Beginning with efforts to prevent volumetric locking, which is a severe shortcoming of traditional low order h-type displacement elements, the investigation proposes the use of the high order p-version of the finite element method. It is shown theoretically and confirmed numerically that this p-method is not only robust in preventing locking, but also provides very accurate results. However, the use of uniformly distributed high order p-elements may be computationally demanding when the size of the problem becomes large. This difficulty is tackled by two main approaches: use of a p-adaptive procedure at the elastic computation stage and use of approximate piecewise linear yield functions. The p-adaptive scheme produces a non-uniform p-distribution and helps to greatly reduce the number of degrees of freedom needed while still guaranteeing the required level of accuracy. The overall gain is that the sizes of the models are reduced significantly and hence also the computational effort. The adoption of piecewise linear yield surfaces helps to further increase the efficiency at the expense of possibly slightly less accurate, but still very acceptable, results. State-of-the-art linear programming solvers based on the very efficient interior point methodology are used. Significant gains in efficiency are achieved. A heuristic, semi-adaptive scheme to piecewise linearize the yield surfaces is then developed to further reduce the size of the underlying optimization problems. The results show additional gains in efficiency. Finally, major conclusions are summarized, and various aspects suitable for further research are highlighted.

Style APA, Harvard, Vancouver, ISO itp.

8

Trần, Thanh Ngọc. "Limit and shakedown analysis of plates and shells including uncertainties". Doctoral thesis, Universitätsbibliothek Chemnitz, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200800256.

Pełny tekst źródła

Streszczenie:

The reliability analysis of plates and shells with respect to plastic collapse or to inadaptation is formulated on the basis of limit and shakedown theorems. The loading, the material strength and the shell thickness are considered as random variables. Based on a direct definition of the limit state function, the nonlinear problems may be efficiently solved by using the First and Second Order Reliability Methods (FORM/SORM). The sensitivity analyses in FORM/SORM can be based on the sensitivities of the deterministic shakedown problem. The problem of reliability of structural systems is also handled by the application of a special barrier technique which permits to find all the design points corresponding to all the failure modes. The direct plasticity approach reduces considerably the necessary knowledge of uncertain input data, computing costs and the numerical error
Die Zuverlässigkeitsanalyse von Platten und Schalen in Bezug auf plastischen Kollaps oder Nicht-Anpassung wird mit den Traglast- und Einspielsätzen formuliert. Die Lasten, die Werkstofffestigkeit und die Schalendicke werden als Zufallsvariablen betrachtet. Auf der Grundlage einer direkten Definition der Grenzzustandsfunktion kann die Berechnung der Versagenswahrscheinlichkeit effektiv mit den Zuverlässigkeitsmethoden erster und zweiter Ordnung (FROM/SORM) gelöst werden. Die Sensitivitätsanalysen in FORM/SORM lassen sich auf der Basis der Sensitivitäten des deterministischen Einspielproblems berechnen. Die Schwierigkeiten bei der Ermittlung der Zuverlässigkeit von strukturellen Systemen werden durch Anwendung einer speziellen Barrieremethode behoben, die es erlaubt, alle Auslegungspunkte zu allen Versagensmoden zu finden. Die Anwendung direkter Plastizitätsmethoden führt zu einer beträchtlichen Verringerung der notwendigen Kenntnis der unsicheren Eingangsdaten, des Berechnungsaufwandes und der numerischen Fehler

Style APA, Harvard, Vancouver, ISO itp.

9

Goodall, Shane. ""Harness Shakedown" Flight Bus Harness Testing Using the CKT Machine". Digital Commons at Loyola Marymount University and Loyola Law School, 2012. https://digitalcommons.lmu.edu/etd/391.

Pełny tekst źródła

Streszczenie:

At the Boeing Satellite Development Center, all programs must follow the same test flow through the factory. First the units are built, tested, and delivered for sub system level integration. There are units built for the bus module and units built for the payload module. Both sub systems are built in different locations and have their own core teams. Once the sub systems are properly integrated, they will then travel to the next test phase of the factory which is known as Integrated Vehicle Testing (IVT). During IVT, both the bus and payload modules are integrated to make one system. This system will travel through the factory and will be tested to make sure that all requirements are met. Once all requirements are validated and verified, the spacecraft is now ready for launch and delivery to the customer. There are hundreds of tests that need to take place throughout the spacecrafts life in the factory. The purpose of these tests is to make sure that a requirement from the customer is met one way or another. Thousands of man hours are budgeted for testing the satellite during its journey through the factory. At an average engineering cost of $200 per hour, this total dollar value for requirements validation and verification can get very expensive. One of the tests in particular is called "Harness Shakedown." This test is conducted to make sure that all the harness wiring in the bus module is wired correctly per the released wire list. These wires can be used for telemetry and control, power to units, signal wires, etc. The way that the test is currently conducted is all done manually using break out boxes, break out cables, digital volt meters, and power supplies. This is an inefficient way of doing the test. This test can be leaned out using systems engineering practices and finding better ways for doing this test to bring value to the customer. The most expensive cost to a program is engineering labor. Systems engineering can help in this test by using the systems engineering process milstd- 499B. This will be used to ensure that the requirements are good and can be fulfilled through the new way of testing. Lean systems engineering will play a large role in finding waste in the test and how to eliminate this non-value added waste. Understanding risk that can occur and ways to manage that risk, is key when fulfilling these requirements. Performing trade studies on how to do this test will help in making the proper engineering decision for the best way of doing the test while again, focusing on added value to the program.

Style APA, Harvard, Vancouver, ISO itp.

10

Trần, Thanh Ngọc. "Limit and shakedown analysis of plates and shells including uncertainties". Doctoral thesis, Bericht ; 2/2008, 2007. https://monarch.qucosa.de/id/qucosa%3A18876.

Pełny tekst źródła

Streszczenie:

The reliability analysis of plates and shells with respect to plastic collapse or to inadaptation is formulated on the basis of limit and shakedown theorems. The loading, the material strength and the shell thickness are considered as random variables. Based on a direct definition of the limit state function, the nonlinear problems may be efficiently solved by using the First and Second Order Reliability Methods (FORM/SORM). The sensitivity analyses in FORM/SORM can be based on the sensitivities of the deterministic shakedown problem. The problem of reliability of structural systems is also handled by the application of a special barrier technique which permits to find all the design points corresponding to all the failure modes. The direct plasticity approach reduces considerably the necessary knowledge of uncertain input data, computing costs and the numerical error.
Die Zuverlässigkeitsanalyse von Platten und Schalen in Bezug auf plastischen Kollaps oder Nicht-Anpassung wird mit den Traglast- und Einspielsätzen formuliert. Die Lasten, die Werkstofffestigkeit und die Schalendicke werden als Zufallsvariablen betrachtet. Auf der Grundlage einer direkten Definition der Grenzzustandsfunktion kann die Berechnung der Versagenswahrscheinlichkeit effektiv mit den Zuverlässigkeitsmethoden erster und zweiter Ordnung (FROM/SORM) gelöst werden. Die Sensitivitätsanalysen in FORM/SORM lassen sich auf der Basis der Sensitivitäten des deterministischen Einspielproblems berechnen. Die Schwierigkeiten bei der Ermittlung der Zuverlässigkeit von strukturellen Systemen werden durch Anwendung einer speziellen Barrieremethode behoben, die es erlaubt, alle Auslegungspunkte zu allen Versagensmoden zu finden. Die Anwendung direkter Plastizitätsmethoden führt zu einer beträchtlichen Verringerung der notwendigen Kenntnis der unsicheren Eingangsdaten, des Berechnungsaufwandes und der numerischen Fehler.

Style APA, Harvard, Vancouver, ISO itp.

11

Jappy, Alan. "A constitutively consistent lower bound, direct shakedown and ratchet method". Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23743.

Pełny tekst źródła

Streszczenie:

When a structure is subject to cyclic loads there is a possibility of it failing due to ratchet or incremental collapse. In many engineering structures the demonstration of non-ratcheting behaviour is a fundamental requirement of the design and assessment process. Whilst it is possible to use incremental finite element analysis to simulate the cyclic response for a given load case to demonstrate shakedown or ratchet, it does not yield any information on the safety factor. In addition, there are several practical problems in using this approach to determine whether or not a component has achieved shakedown. Consequently several direct methods which find the loads at the shakedown and ratchet boundaries have been developed in the past 3 decades. In general, lower bound methods are preferred for design and assessment methodologies. However, to date, the lower bound methods which have been proposed for shakedown and ratchet analysis have not been fully reliable and accurate. In this thesis a lower bound shakedown and ratchet method which is both reliable and accurate is proposed. Previously proposed elastic plastic lower bound ratchet methods are revisited and modified to understand the limitations in current methods. From this, Melan's theorem is reinterpreted in terms of plasticity modelling and shown to have the same form as a non-smooth multi yield surface plasticity model. A new shakedown method is then proposed based on the non-smooth multi yield surface plasticity model. The new shakedown method is extended using a two stage process to determine the ratchet boundary for cyclic loads in excess of the alternating plasticity boundary. Two simplified variants of the ratchet method are also proposed to decrease the computational expense of the proposed ratchet method. Through several common benchmark problems the proposed methods are shown to give excellent agreement with the current upper bound methods which have been demonstrated to be accurate. The flexibility of the shakedown method is demonstrated by extending the method to incorporate temperature dependent yield, hardening and simplified non-linear geometric effects.

Style APA, Harvard, Vancouver, ISO itp.

12

Martinez, Julian A. "Weiser Carrots and Sticks: Motivation Beyond Money at the Shakedown Café". Scholarship @ Claremont, 2012. http://scholarship.claremont.edu/cmc_theses/411.

Pełny tekst źródła

Streszczenie:

It is generally assumed that monetary incentivization is the most effective means of motivating organizationally-beneficial behaviors. Individuals, under this line of thought, pursue their own objective self-interest above all else. However, evidence is being uncovered that indicates that human motivation may be a much more complicated facet of the human psyche. The purpose of this study is to examine the deeper underpinnings that drive people work that might lie beyond financial rewards. In order to do this, the Shakedown Café, a student-run restaurant on Pitzer College’s campus, will be examined. This specific organization is of particular interest because it does not have the ability to reward employees in the manner that most businesses are able to employ. In looking at the Shakedown, the author's direct experiences while working in the restaurant, observations, a variety or intra-organizational correspondences, and modern organizational behavior theories will be utilized. The findings of this research indicate that the human drives to learn, bond with others, and defend oneself and one's surroundings are all just as important aspects of motivation as is the drive to acquire money. Within the organization of interest, these drives manifest themselves through organizational purpose, group learning, and shared leadership. From this example of the Shakedown Café, it is suggested that proliferation of financial rewards in today's organizations may well be an outdated model of motivating which could be prohibiting organizations and the people within them from reaching their full potentials.

Style APA, Harvard, Vancouver, ISO itp.

13

Shi, Jinhua. "Limit and shakedown analysis of structures by the finite element method". Thesis, University of Strathclyde, 1996. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=21253.

Pełny tekst źródła

Streszczenie:

Limit and shakedown analyses are powerful methods in designing pressure vessel components and other engineering structures. With the development of computer technology the use of finite element analysis as an alternative tool for engineering structure design has become ever more increasing. In this thesis the finite element method utilises the novel elastic compensation method to carry out the limit and shakedown analyses on variety engineering structures: nozzles in pressure vessels, plates with a central hole and frame structures. There are two main objectives of the present study. One of them is to conduct limit and shakedown analyses on a series of thick cylinders, nozzle/sphere intersections under internal pressure, plates with a hole and frame structures under multiple loading conditions using the initially developed elastic compensation method based on 2-D solid element models. A comparision of the lower, upper bound limit loads and shakedown solutions is made with the result s available in literature or with new elasto-plastic analyses. The results obtained using the elastic compensation method were found to be of useful accuracy. Another is to further develop the elastic compensation method using generalised yield criteria. Then the procedure is implemented to beam and shell finite elements to calculated limit loads for beam and shell structures. A number of 2-D and 3-D frames were examined using a general yield surface. The obtained results were compared with that of theoretical plastic analysis and with the results available in literature and were found to be in good agreement. Parametric studies of nozzle/sphere intersections and nozzle/cylinder intersections under internal pressure were carried out using Ilyushin's and Ivanov's generalised yield criteria. The results calculated were compared with the solutions obtained using the initially elastic compensation method and with the solutions available in literature and were found to also be in good agreement. The newly developed elastic compensation procedure using generalised yield criteria was found to be more economic and useful in engineering design. From this study, some new design methods based on limit and shakedown loads are proposed for nozzle/sphere intersections and for other engineering structures. The newly developed elastic compensation procedure using generalised yield criteria is highly recommended in structural design for a quick limit load estimation.

Style APA, Harvard, Vancouver, ISO itp.

14

Juspi, Sumyaty. "Experimental validation of the shakedown concept for pavement analysis and design". Thesis, University of Nottingham, 2007. http://eprints.nottingham.ac.uk/12864/.

Pełny tekst źródła

Streszczenie:

The shakedown concept has been widely applied in structural and mechanical engineering numerical models. The concept is related to the response of a structure to load repetitions in a resilient manner without further permanent deformation. More than 40 wheel tracking tests were conducted with various wheel load levels for each test to check the validity of the shakedown concept in the pavement foundation. Six different types of soils with different characteristics were used in the wheel tracking tests. These were a silt (from gravel pit washings), a silty-clay (Mercia Mudstone, referred to here by its earlier name of Keuper Marl), two sands (Portaway and Langford Fill), and two crushed rocks (Carboniferous Limestone and Granite). Three different sized wheel-tracking facilities were used; a small wheel tracker (SW), a larger Slab Testing Facility (STF) and the half-scale Nottingham Pavement Testing Facility (PTF). These allowed various wheel specifications and test specimen sizes to be investigated. The test programme embraced one, two and three layered systems. The permanent vertical deformation of each system was measured after a certain number of passes. The soil is said to be under shakedown if after a certain number of passes, there is no further permanent deformation. The experimental result was compared with the theoretical shakedown prediction. A series of static triaxial tests for each soil, with the test conditions close to the wheel tracking tests, was carried out to identify the shear strength to be used as input parameters for the theoretical shakedown prediction. The theoretical shakedown limits of the various soil combinations show a good agreement with the wheel tracking test results.

Style APA, Harvard, Vancouver, ISO itp.

15

Liu, Shu. "Application of shakedown theory in the structural design of bituminous pavements". Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/35577/.

Pełny tekst źródła

Streszczenie:

Excessive rutting, one of the major distress modes of bituminous pavements, is mainly caused by the accumulation of load-induced permanent deformation. However, current pavement design approaches against the excessive rutting are mainly developed using the theory of elasticity. Recently, a new pavement design approach based on the shakedown concept has attracted lots of attention because it can consider plastic properties of pavement materials. However, most of the existing shakedown solutions were developed for pavement foundations composed of granular materials and soils. Very limited work has been reported on bituminous pavements. Besides, current studies usually assume homogeneous, isotropic pavement materials obeying an associated plastic flow rule (termed as standard materials in the present study), which may not be realistic for pavement materials. In the present research, a step-by-step numerical approach was used to obtain numerical shakedown limits of pavement structures under repeated moving loads. Both two-dimensional and three-dimensional problems were considered. It was found that, under the assumption of standard materials, the obtained numerical shakedown limits and residual stress fields agreed well with the available theoretical data. A static (i.e. lower bound) shakedown approach for pavements with anisotropic, heterogeneous materials was developed based on Melan’s lower bound theorem and the critical residual stress method of Yu and Wang (2012). The influence of material plastic flow rules on pavement shakedown limits was also evaluated both numerically and theoretically. It was found that neglect of the inherent material properties (i.e. anisotropy, heterogeneity and non-associated plastic flow) could overestimate the real shakedown limits of bituminous pavements. A series of tests were conducted to validate the shakedown concept for the responses of bituminous pavements under traffic loads. Two distinct phenomena corresponding to shakedown and non-shakedown were observed. Triaxial tests and uniaxial compression tests were also undertaken to obtain the stiffness and strength parameters, from which the theoretical shakedown limits can be calculated. Comparison between the experimental results and the theoretical solutions revealed that the current 3D shakedown approach for standard materials may overestimate capacities of bituminous pavements. Finally, the lower bound shakedown approach was employed to design a typical bituminous pavement. A direct comparison was made between the shakedown-based design and the current UK design method. It demonstrated that the shakedown-based design for bituminous pavements can be conducted considering the maximum contact pressure and a relatively high air temperature.

Style APA, Harvard, Vancouver, ISO itp.

16

Wang, Juan. "Shakedown analysis and design of flexible road pavements under moving surface loads". Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/12836/.

Pełny tekst źródła

Streszczenie:

Flexible road pavements often fail due to excessive rutting. as a result of cumulative vertical permanent deformation under repeated traffic loads. The currently used analytical approach to flexible pavement design evaluates the pavement life in terms of critical elastic strain at the top of the subgrade. Hence, the plastic pavement behaviour is not properly considered. Shakedown analysis can take into account the material plasticity and guarantee structure stability under repeated loads. It provides a more rational design criterion for flexible road pavements. Finite element analyses using the Tresca and Mohr-Coulomb yield criteria are performed to examine the responses of soil half-space when subjected to different loading levels. Both shakedown and surface ratchetting phenomena are observed and the residual stresses are found to be fully-developed after a limited number of load passes. The finite element results are then used to validate the solutions from shakedown analysis. The main focus of current research is concerned with new solutions for static (i.e. lower-bound) shakedown load limits of road pavements under both two-dimensional and three-dimensional moving surface loads. Solutions are derived by limiting the total stresses at any point (i.e. residual stresses plus loading induced elastic stresses) to satisfy the Mohr-Coulomb yield criterion. Previous analytical shakedown solution has been derived based on a residual stress field that may not satisfy equilibrium for certain cases. In this study, a rigorous lower-bound shakedown solution has been derived by imposing the equilibrium condition of residual stresses. The newly developed shakedown solutions have been applied to one-layered and multi-layered pavements. It was found that the rigorous lower-bound solution based on the self-equilibrated residual stress field is lower than the analytical shakedown solution for cases when the critical point lies on the surface or at the base of the first pavement layer. The results showed that the theoretical predictions of pavement shakedown load limit generally agree with the finite element and experimental observations for pavement behaviours. The shakedown solution has been further extended to study the influence of the shape of contact load area for pavements under three-dimensional Hertz loads. It was found that the shakedown load limit can be increased by changing the load contact shape from a circle area to an elliptical one. A new pavement design approach against excessive rutting has been proposed. The pavement design is suggested by plotting thickness design charts using the direct shakedown solutions and choosing the thickness combination based on the design traffic load.

Style APA, Harvard, Vancouver, ISO itp.

17

Crawley, Nigel Ian. "The effect of proof testing on the shakedown behaviour of pressure vessel components". Thesis, University of Liverpool, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240528.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

18

Merkevičiūtė, Dovilė. "Tamprių-plastinių prisitaikančių sistemų optimizacija su standumo ir stabilumo sąlygomis". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2005. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2005~D_20051223_165845-93934.

Pełny tekst źródła

Streszczenie:

Optimization problems (to which is dedicated this dissertation) of structural mechanics are introductory stage of structure optimum design based on principles of solid deformable body mechanics, mathematical programming theory, its methods and their mechanical interpretation. In order to base calculation on real operating conditions of structure, it is necessary evaluate as exact as possible structure material properties, external effects and other factors in mathematical models of optimization problems. Partially it is achieved by including plastic properties of material. Calculation and design of the structures, taking in to account plastic strains, allows to use their bearing capacity more efficiently and make more economic project (in this dissertation research is developed on the basis of perfect plasticity theory). From the other side, real effect for structure are often cyclic (variable repeated load character is also evaluated in this work). In the dissertation it is assumed that load is quasi–static and is characterised by load variation bounds (deterministic formulation of problems is considered). Under repeated loading a structure can lose its serviceability because of its progressive plastic failure or because of alternating strain (usually both cases are called cyclic–plastic collapse). But, if residual forces together with variable part that do not violate the admissible bounds appear in the initial stage of loading, the structure adapts to existing load and... [to full text]

Style APA, Harvard, Vancouver, ISO itp.

19

Nery, Domingos Eugênio de Sá, i Instituto de Engenharia Nuclear. "Estados limite de componentes mecânicos considerando encruamento cinemático limitado". Instituto de Engenharia Nuclear, 2007. http://carpedien.ien.gov.br:8080/handle/ien/1950.

Pełny tekst źródła

Streszczenie:

Submitted by Marcele Costal de Castro (costalcastro@gmail.com) on 2017-10-02T17:55:20Z No. of bitstreams: 1 DOMINGOS EUGENIO DE SÁ NERY D.PDF: 2789497 bytes, checksum: aff82f3bd13e62b597c33ec7477538fb (MD5)
Made available in DSpace on 2017-10-02T17:55:20Z (GMT). No. of bitstreams: 1 DOMINGOS EUGENIO DE SÁ NERY D.PDF: 2789497 bytes, checksum: aff82f3bd13e62b597c33ec7477538fb (MD5) Previous issue date: 2007-08
Neste trabalho o problema da acomodação elástica de enfocado, para estruturas constituídas de materiais de Mises, porém com a consideração do encruamento cinemático limitado. O modelo de camadas de microelementos de Stein é utilizado para a formulação e solução do problema e é mostrado que o algoritmo já desenvolvido para o caso de elastoplasticidade ideal, pode ser utilizado também no caso com encruamento. As soluções analíticas, desenvolvidas para o problema de um bloco com restrições, são estendidas para o caso com encruamento e permitem a validação dos resultados numéricos em tensão plana. Comparações com resultados da literatura são levadas a efeito, tanto em tensão plana quanto em problemas com simetria de revolução. Estes exemplos visam à validação da teoria e sua implementação e também o tratamento de estruturas mais complexas que se aproximem progressivamente do nível das aplicações industriais.
In this work, the problem of shakedown is considered for Mises material structures but, with limited kinematic hardening. Stein's overlay model is used for formulation and solution of the problem. It is shown that the algorithm, originally developed for elastic perfectly plastic materials, can be used when hardening is considered. Analytical solutions developed for a restrained block are extended here for the case of hardening in plane stress, allowing the validation of numerical results. Bench marks are used to check numerical results in plane stress and axissimetric problems. This examples intend to validate the theory and its implementation and also a progressive treatment of more complex structures, aiming to approach industrial level.

Style APA, Harvard, Vancouver, ISO itp.

20

Morrissey, Ryan J. "Strain accumulation and shakedown in fatigue of Ti-6A1-4V by Ryan J Morrissey". Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17144.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

21

GONCALVES, R. P. "ESTUDO NUMÉRICO DO EFEITO DE PROPRIEDADES MECÂNICAS E DO ATRITO NO FENÔMENO DE SHAKEDOWN". Universidade Federal do Espírito Santo, 2016. http://repositorio.ufes.br/handle/10/9731.

Pełny tekst źródła

Streszczenie:

Made available in DSpace on 2018-08-02T00:02:50Z (GMT). No. of bitstreams: 1 tese_10432_RODRIGO PEREIRA GONÇALVES.pdf: 3395928 bytes, checksum: a1eb1bfe65858f3c3f79d97f9029e049 (MD5) Previous issue date: 2016-09-29
Shakedown pode ser definido como o processo pelo qual uma estrutura submetida a um carregamento cíclico, que se deforma plasticamente durante a primeira aplicação de carga, atinge após uma determinada quantidade de ciclos um estado estacionário em que a resposta do material é perfeitamente elástica. Uma estrutura projetada com base em uma análise shakedown é mais segura do que uma baseada em seu limite plástico. Dessa forma, foi feito um estudo numérico afim de avaliar a inflência de parâmetros como tensão de escoamento, coeficiente de atrito, grau de encruamento e modelo de encruamento no fenomemo shakedown. Para isso, foi utilizado o software comercial ABAQUS, onde foi feito um modelo de elementos finitos para simular um carregamento cíclico de uma esfera rígida sobre um plano deformável. Os resultados indicam que quanto mais resistente é o material solicitado (maior tensão de escoamento) mais rápido acontece a estabilização em shakedown. O atrito se mostra prejudicial ao acontecimento do shakedown, aumentando a quantidade de ciclos de carregametno necessários para sua estabilização. Já o encruamento teve uma influência benéfica, facilitando o acontecimento do fenômeno. Os modelos de encruameno isotrópicos e cinemático linear se mostraram inadequados para análise em condições que envolvem alta deformação plástica, não sendo capazes de prever a plasticidade incremental. Já o modelo de encruamento cinemático não-linear se mostrou adequado para análise shakedown em todas as condições simuladas. Palavras chave: Shakedown, Atrito, Modelo de encruamento

Style APA, Harvard, Vancouver, ISO itp.

22

Tong, Andrew S. "Design, Shakedown, Modification, and Preliminary Study of the Sygnas Chemical Looping Sub-Pilot Demonstration Unit". The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1284999534.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

23

Ribeiro, Madalena Maria Pereira. "Contribuição ao estudo da deformação permanente dos solos de subleito". Universidade de São Paulo, 2013. http://www.teses.usp.br/teses/disponiveis/18/18143/tde-06092013-110219/.

Pełny tekst źródła

Streszczenie:

Esta pesquisa apresenta uma contribuição ao entendimento do efeito da variação do estado de tensões e variação de umidade na compactação, na suscetibilidade à deformação permanente dos solos de subleito. Assim, um programa experimental foi desenvolvido considerando as variáveis o estado de tensões e a umidade, que são importantes na análise da evolução da deformação permanente dos solos de subleito. Para esta avaliação, foi utilizado um solo arenoso laterítico proveniente da região de Dois Córregos, estado de São Paulo, Brasil. Foram realizados ensaios de caracterização e ensaios triaxiais de cargas repetidas (módulo de resiliência e deformação permanente). Adicionalmente, foi analisado o efeito do acúmulo de deformação permanente nos valores de módulo de resiliência, que foi efetuado a partir de ensaios realizados antes e após o ensaio de deformação permanente. Além disso, de posse dos resultados de deformação permanente foi verificada a ocorrência do Shakedown. Concluiu-se que um aumento de tensões causa um aumento na deformação permanente, não sendo possível avaliar o efeito da variação de umidade na deformação permanente. Observou-se a ocorrência do Shakedown, porém não foi possível definir seu limite. Não foi possível o enquadramento da deformação permanente no modelo de Monismith, sendo proposto, por meio de regressão múltipla, um modelo para avaliação da deformação permanente, considerando as variáveis, umidade, número de aplicações de carga e estado de tensões.
This research presents a contribution to understanding the effect of the variation of the state of stress and water content in the evolution of the permanent deformation of subgrade soils. A lateritic sandy soil from the region of Dois Córregos, State of São Paulo, Brazil, was used throughout the characterization and triaxial repeated loads tests (resilient module and permanent deformation tests). Additionally, it was analyzed the effect of the accumulation of permanent deformation in the values of resilient module from tests performed before and after the permanent deformation tests, as well as it was verified the occurrence of Shakedown. It was concluded that an increase of stress causes an increase in permanent deformation, but it was not possible to evaluate the effect of the variation of moisture content in permanent deformation. It was also observed the occurrence of Shakedown, but it was not possible to set its limit. Furthermore, it was not possible to fit the permanent deformation testing data in the model of Monismith, being proposed, by means of multiple regression, a model for the assessment of permanent deformation considering the variables moisture content, number of load applications and state of stress.

Style APA, Harvard, Vancouver, ISO itp.

24

Tran, Ngoc Trinh [Verfasser], i Hermann G. [Akademischer Betreuer] Matthies. "Limit and Shakedown Analysis of Structures under Stochastic Conditions / Ngoc Trinh Tran ; Betreuer: Hermann G. Matthies". Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/1177988585/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

25

Barros, Felicio Bruzzi. "Técnica adaptativa de elementos finitos para análise limite e de "Shakedown" para cascas finas axi-simétricas". Universidade Federal de Minas Gerais, 1996. http://hdl.handle.net/1843/PASA-8AEHCS.

Pełny tekst źródła

Streszczenie:

Improvements in the technique for finite element shakedown and limit analysis of axisymmetrical shells, proposed by [Franco, 1987], are presented. Basic concepts of the continuum mechanics are first summarized and the technique is introduced.l The stress problem due to the temperature gradient at the contact of a supporting skirt of a coke drum is analyzed. The elastic solution obtained from the thin shell theory was implemented for considering indirect load. An error estimator combined with adaptive procedures for an h-refinement are presented to obtain much more reliable solutions.A new finite element compatible with a more sophisticated yield surface is developed. Although the formulation for a complete shakedown analysis has not been implemented, limit analysis problems were studied for each proposed topic which illustrate the effectiveness and quality of the formulations.
Este trabalho descreve as contribuições realizadas para a técnica de elementos finitos de análise limite e de "shakedown"em casca axi-simétricas, proposta em [ Franco, 1987 ]. Após uma breve revisão de conceitos fundamentais e da apresentação da técnica, é feito um estudo simplificado da saia de sustentação de um tambor de coqueamento, sujteita a tensões provenientes de sua interação com o tambor, durante a produção do coque. Para a consideração do carregamento indireto, foram utilizadas soluções elásticas da teoria de cascas finas. Em seguida, com a finalidade de melhorar a solução numérica, através de uma estratégia adaptativa do tipo h, é desenvolvido um estimador de erro. Finalmente, a formulação de um novo elemento finito e de condições de escoamento mais sofisticadas são introduzidas. Embora a formulação para uma análise de "shakedown"completa não tenha sido implementada, problemas de análise limite foram estudados para cada um dos tópicos propostos demonstrando o sucesso das implementações efetuadas.

Style APA, Harvard, Vancouver, ISO itp.

26

Phạm, Phú Tinh [Verfasser]. "Upper bound limit and shakedown analysis of elastic-plastic bounded linearly kinematic hardening structures / Phu Tinh Pham". Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2011. http://d-nb.info/1018189491/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

27

Ure, James Michael. "An advanced lower and upper bound shakedown analysis method to enhance the R5 high temperature assessment procedure". Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=22547.

Pełny tekst źródła

Streszczenie:

A nuclear power station contains some of the most extreme environments and operating conditions seen by metallic components. In order to ensure the continued safe operation of these plant components rigorous structural integrity assessments are performed. Part of this structural assessment involves demonstrating that the component in question will not fail by ratcheting. In the UK the R5 procedure forms the cornerstone of these integrity assessments. The R5 rules for shakedown, whilst easily implemented, can give an overly pessimistic estimate of the shakedown status. This means that a computationally expensive nonlinear finite element analysis must be conducted. The Linear Matching Method (LMM) is one of the recently developed Direct Methods for shakedown analysis. This upper bound method has the ability to give more accurate shakedown limits than the simplified R5 route and with less computational expense than nonlinear finite element analysis. This thesis details the steps taken to take the LMM from being a research based method into a tool which can be used for regular integrity analyses within EDF. Firstly a conservative lower bound to the shakedown limit is derived and added to the LMM. The theoretical development and numerical implementation of this calculation is detailed. Convergence improvements are also investigated to improve the numerical difficulties often suffered by lower bound shakedown calculations. The LMM is implemented in Abaqus through user subroutines. To make the LMM suitable for regular use a user interface has been created via a plug-in for Abaqus. This plug-in automatically configures the model for the analysis, meaning that the user now has access to LMM analyses without having to carry out the code changes which were required with the research version of the method. The resulting analysis tool has been delivered to EDF so their engineers can now access accurate shakedown analyses through a convenient user-interface.

Style APA, Harvard, Vancouver, ISO itp.

28

Jospin, Reinaldo Jacques, i Instituto de Engenharia Nuclear. "Etats limites des tuyauteries par la methode des elements finis et la programmation mathematique". Instituto de Engenharia Nuclear, 1992. http://carpedien.ien.gov.br:8080/handle/ien/1956.

Pełny tekst źródła

Streszczenie:

Submitted by Marcele Costal de Castro (costalcastro@gmail.com) on 2017-10-04T18:02:21Z No. of bitstreams: 1 REINALDO J. JOSPIN D.pdf: 7139084 bytes, checksum: bf9d60aa6ce4a1c288149571d9f29f14 (MD5)
Made available in DSpace on 2017-10-04T18:02:21Z (GMT). No. of bitstreams: 1 REINALDO J. JOSPIN D.pdf: 7139084 bytes, checksum: bf9d60aa6ce4a1c288149571d9f29f14 (MD5) Previous issue date: 1992
Les tuyauteries sont parmi les structures les plus utilisées dans la construction mécanique et dans des domaines aussi variés que ceux des installations nucléaires, des structures "offshore", de Pindustrie pétrochimique, etc... Ces structures, composées essentiellement de tuyaux droits (coque cylindrique) et de coudes (coque toroïdale incomplète), sont soumises à des expansions thermiques, à des séismes, à leur poids propre, à des effets de raccordement, etc....Une analyse particulièrement poussée des coudes, ses composants les plus flexibles, est nécessaire en vue de déterminer les déplacements apparus lors du chargement. Plus particulièrement, pour des matériaux rigides plastiques et pour des chargements proportionnels (analyse limite) dans le cas des tuyaux cylindriques, et dans le cas des coudes. Ces derniers utilisent une analyse viscoplastique où le cas particulier du matériau rigide plastique est obtenu à la limite quand l'exposant de la loi de comportement tend vers l'infini. Le problème crucial de la stabilité de l'ovalisation d'un coude de section circulaire et soumis à une pression interne utilisant les différences finies utilisant l'intégration numérique directe effectuée sur les équations de Reissner pour les petites déflexions finies. En ce qui concerne la modélisation et le calcul numérique des coudes, on constate dans la littérature deux voies complémentaires. La première consiste à discrétiser le coude em éléments finis de coques (bidimensionnelles ou tridimensionnelles). Dans ce cas, les effets géométriques d'ovalisation et de gauchissement de la section sont pris en compte directement. La deuxième utilise des éléments de poutre (umdimensionnels) avec des champs de déplacement enrichis par des champs qui peuvent représenter l'ovalisation et le gauchissement. La théorie de l'analyse limite considère l'état de ruine plastique des structures soumises à des charges proportionnelles croissantes, c'est à dire, dépendantes d'un seul paramètre. Généralement les charges appliquées aux structures varient indépendamment et de façon répétitive. La deuxième méthode prend aussi un grand élan surtout dans la théorie unifiée des états limites l'analyse linéaire, l'analyse limite et l'adaptation plastique car elle est plus économique pour ce qui concerne le coût numérique. Au niveau du critère de plasticité, les utilisateurs de la méthode de Newton travaillent directement sur des critères non linéaires du type von Mises tandis que les partisans de la programmation mathématique dans la majorité formulent les problèmes avec des critères linéarisés. Au niveau des variables, les premiers éliminent les variables internes (déformation plastique) au profit des variables structurales (déplacement), alors que les seconds éliminent les déplacements en ne conservant que les variables internes (le multiplicateur plastique).

Style APA, Harvard, Vancouver, ISO itp.

29

Trần, Thanh Ngọc. "Limit and shakedown analysis of plates and shells including uncertainties Traglast- und Einspielanalyse von Platten und Schalen bei Unsicherheiten /". [S.l. : s.n.], 2008.

Znajdź pełny tekst źródła

Streszczenie:

Chemnitz, Techn. Univ., Diss., 2008.
Zugl. ersch. als: Bericht, Technische Universität Chemnitz, Fakultät für Maschinenbau, Institut für Mechanik und Thermodynamik ; 2/2008. - Dt.-Titel: Traglast- und Einspielanalyse von Platten und Schalen bei Unsicherheiten.

Style APA, Harvard, Vancouver, ISO itp.

30

Merkevičiūtė, Dovilė. "Tamprių-plastinių prisitaikančių sistemų optimizacija su standumo ir stabilumo sąlygomis". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2006. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2005~D_20060209_120302-36691.

Pełny tekst źródła

Streszczenie:

Optimization problems (to which is dedicated this dissertation) of structural mechanics are introductory stage of structure optimum design based on principles of solid deformable body mechanics, mathematical programming theory, its methods and their mechanical interpretation. In order to base calculation on real operating conditions of structure, it is necessary evaluate as exact as possible structure material properties, external effects and other factors in mathematical models of optimization problems. Partially it is achieved by including plastic properties of material. Calculation and design of the structures, taking in to account plastic strains, allows to use their bearing capacity more efficiently and make more economic project (in this dissertation research is developed on the basis of perfect plasticity theory). From the other side, real effect for structure are often cyclic (variable repeated load character is also evaluated in this work). In the dissertation it is assumed that load is quasi–static and is characterised by load variation bounds (deterministic formulation of problems is considered). Under repeated loading a structure can lose its serviceability because of its progressive plastic failure or because of alternating strain. But, if residual forces together with variable part that do not violate the admissible bounds appear in the initial stage of loading, the structure adapts to existing load and further behaves elastically. This phenomenon is... [to full text]

Style APA, Harvard, Vancouver, ISO itp.

31

Li, Kai. "Modélisation du comportement hydromécanique des sols gonflants basée sur la théorie de l'état limite". Thesis, Strasbourg, 2015. http://www.theses.fr/2015STRAD004/document.

Pełny tekst źródła

Streszczenie:

Les matériaux argileux sont soumis aux chemins complexes de succion/contrainte qui se manifestent par des désordres affectant principalement les structures construites en surface et les ouvrages enterrés. Dans ce contexte, il est important d’appréhender le comportement hydromécanique de ces matériaux afin de mieux maîtriser leur utilisation. Le comportement hydromécanique complexe des matériaux argileux est directement relié à leur structure interne qui a été le principal sujet de plusieurs études sur la micro- et macrostructure des sols. Ces études ont conduit aux développements des modèles élastoplastiques pour sols gonflants. Les modèles existants sont capables de simuler le comportement principal de sol gonflant non saturé, mais ils présentent un grand nombre de paramètres, ce qui prend du temps pour le calcul. Par conséquence, on propose une méthode simplifiée pour modéliser le comportement hydromécanique des sols gonflants basée sur la théorie de l’état limite. Ce modèle est tout d’abord validé par les résultats de l’essai oedométrique. Ensuite, il est implanté dans un code aux éléments finis (CAST3M) pour simuler le comportement in situ des sols gonflants. Enfin, l’application de la théorie de l’état limite au sol gonflant avec une grande densité est effectuée par la combinaison de l’écrouissage cinématique et l’écrouissage isotrope
Clayey materials are often subjected to the complex suction/stress paths, causing many problems in both surface structures and buried structures built on them. In this context, it is important to study the hydromechanical behavior of these materials in order to better control their use in civil engineering. The complex hydromechanical behavior of clay materials is basically connected to their fabric which has been the main subject of several studies on the micro- and macrostructure of soils. These studies have led to the development of elastoplastic models for expansive soils. The existed models are able to simulate the basic behavior of unsaturated expansive soil, but present a large number of model parameters, leading to a time-consuming calculation. Therefore, we propose a simplified method to model the hydromechanical behavior of expansive soils based on shakedown concept. This model is first validated by the experimental results of cyclic suction-controlled oedometer tests. Then, it is implemented in a finite element code (CAST3M) to simulate the in-situ behavior of expansive soils. Finally, the application of shakedown theory to heavily dense expansive soils is carried out by considering a combined hardening plasticity

Style APA, Harvard, Vancouver, ISO itp.

32

Zago, João Paulo. "Estudo da deformação permanente de três solos típicos de subleitos rodoviários de Santa Maria - RS". Universidade Federal de Santa Maria, 2016. http://repositorio.ufsm.br/handle/1/12036.

Pełny tekst źródła

Streszczenie:

Studies conducted in 2016 show that 58% of the highways in Brazil presents any deficiency in the pavement, signaling or in its geometry. These deficiencies are, on average, the cause for about 6% of the accidents and for the increase of the operational cust by 91,6%. Among them we can stress the permanent deformation, the so called wheel tracks, which is harmful to the dynamic of the loads, to the comfort provided by the pavement, increasing its risk. To the correct design of the pavement it is very important to better know the characteristics of the materials to be used. In this context, stands out the subgrade, the foundation for the whole structure of the pavement, which one is studied in the present reseach by considering three typical soils used as highway subgrade in Santa Maria, Rio Grande do Sul State, and having the permanent deformations as the main focus. The metodology aplied in this work consisted in the location, sampling and characterization of the soil fields, lab tests and empirical machanistic design. Besides the physical, chemical and mechanical characterizations, it was performed the repeated triaxial load test aiming to obtain the resilient modulus and the permanent deformation parameters, according to the Brazilian Petroleum Corporation Manual (PETROBRAS). The Resilient Modulus model presented the better results with frequencies of 1 Hz and 2 Hz, and the presence of silt in one of the soils affected its resilient behaviour. The permanent deformation tests were performed with the frequency of 2 Hz and 150.000 load cicles. The average statistic correlation, according to Guimaraes (2009)´s methodology, was 0.91, bigger than the one provided by the Monismith and Barksdale´s models. However, the dominance of fine grained soils, along with low compactation energy, lead to a higher deformation rates, motivating the use of intermediate energy. With this new approach the permanent deformation was reduced 40% and the resilient modulus increased 78,8%. However, the numerical simulation according to the mechanistic approach, and using the layer thickness obtained from the Departamento Nacional de Infraestrutura de Transportes (DNIT) method, under 8,2 ton standard axle load, showed that the wheel tracks deeping would be small, based on the low stresses observed in the subgrade. On the other hand, the fatigue behaviour presented an inferior performance, reducing the project´s useful life. It was observed the presence of shakedown in the ranges A, B and C.
Pesquisas realizadas no ano de 2016 mostram que 58,2 % das rodovias de todo o país apresentam alguma deficiência no pavimento, na sinalização ou na geometria da via. Em média, esses defeitos são responsáveis por cerca de 6% do número de acidentes, além de aumentar o custo operacional das vias em até 91,6%. Dentre essas anomalias, destaca-se a deformação permanente denominada de afundamento na trilha de roda (ATR), que prejudica a dinâmica das cargas, afeta o conforto ao rolamento e causa risco à segurança. Para o adequado dimensionamento de um pavimento, é fundamental o conhecimento dos materiais que o compõem. Neste contexto, destaca-se o subleito, por ser a fundação sobre a qual são assentes todas as camadas, motivo pelo qual o objetivo geral desta pesquisa é analisar três solos típicos de subleitos rodoviários de Santa Maria, estado do Rio Grande do Sul, em especial quanto aos parâmetros de deformação permanente. A metodologia aplicada neste trabalho consistiu na localização, coleta e caracterização das jazidas de solos, realização de ensaios laboratoriais e dimensionamento mecanístico - empírico. Assim, além da caracterização física, química e mecânica, foram realizados ensaios triaxiais de cargas repetidas para obtenção do módulo de resiliência e dos parâmetros de deformação permanente, segundo recomendações do manual de execução de trechos monitorados da empresa Petróleo Brasileiro Sociedade Anônima (PETROBRAS). O modelo composto do módulo de resiliência apresentou os melhores resultados, a partir de ensaios com frequência de 1 Hz e 2 Hz, sendo que a presença de silte em um dos solos afetou seu comportamento resiliente. Os ensaios de deformação permanente foram conduzidos a 2 Hz, com 150.000 ciclos de aplicação de carga, cuja correlação estatística média, empregando a metodologia de Guimarães (2009), foi de 0,91 – superior a dos modelos de Monismith e Barksdale. Entretanto, a predominância de materiais finos, aliada à baixa energia de compactação (normal), resultaram em elevadas taxas de deformação, o que motivou o estudo de um dos solos também com uso da energia intermediária. Esse procedimento reduziu a deformação permanente em 40% e elevou o módulo de resiliência em 78,8%. Entretanto, a simulação numérica do pavimento sob a ótica mecanicista, a partir das espessuras calculadas pelo método do Departamento Nacional de Infraestrutura de Transportes (DNIT), aplicando-se a carga padrão de 8,2 toneladas, mostrou que o ATR seria pequeno, em face das baixas tensões atuantes no subleito, em contraposição ao desempenho à fadiga, que reduziu sensivelmente a vida útil de projeto. Constatouse a ocorrência de shakedown nos domínios A, B e C.

Style APA, Harvard, Vancouver, ISO itp.

33

Numrich, Ralf. "Modellierung des nichtlinear-elastischen Verformungsverhaltens von Tragschichten ohne Bindemittel". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2003. http://nbn-resolving.de/urn:nbn:de:swb:14-1073899777906-02092.

Pełny tekst źródła

Streszczenie:

Ziel der vorliegenden Dissertation war die Erweiterung der Kenntnisse über das nichtlinear-elastische Spannungs-Verformungsverhalten von Tragschichten ohne Bindemittel (ToB). Ein analytisches Bemessungsverfahren ist aufgrund der schwierigen Modellierbarkeit des Verformungsverhalten der einzelnen Straßenbaustoffe bisher nicht existent. Die Dissertation soll einen Beitrag zur Entwicklung eines solchen Bemessungsverfahrens leisten. Eine Literaturrecherche zum Verformungsverhalten von ToB bildet die Grundlage für die Festlegung der Vorgehensweise. Basis der weiteren Untersuchungen sind Triaxialversuche, die an der Universität Nottingham an verschiedenen Gesteinskörnungen durchgeführt wurden. Mit Hilfe der Shakedown-Theorie konnte belegt werden, dass sich ToB in unterschiedlichen Beanspruchungsbereichen nach verschiedenen Gesetzmäßigkeiten verhalten und dass Modelle zur Beschreibung des Verformungsverhaltens von ToB bereichsweise verschieden formuliert werden müssen. Somit ist es möglich, Gültigkeitsgrenzen für elastische Stoffmodelle zu ermitteln sowie Beanspruchungsgrenzen für ToB festzulegen. Mit ausgewählten Stoffmodellen erfolgten Beanspruchungsberechnungen nach der Finite-Elemente Methode (FEM). Die beste Annäherung zwischen Messwerten und Rechenergebnissen ergibt sich bei Anwendung des DRESDNER Modells. Berechnungen für Befestigungen nach den RStO 01 haben gezeigt, dass die Beanspruchungen auf den ToB bei Anwendung des DRESDNER Modells stark von denen bei Anwendung linearer Elastizität abweichen können. Durch unterschiedliche Überbauungsdicken der ToB besitzen diese einen verschieden hohen Anteil am Tragverhalten der Befestigung. Abschließend wird eine Methode zur Ermittlung von Sicherheitsniveaus vorgestellt. Bei Kenntnis der entsprechenden Schichtparameter lassen sich die Beanspruchungen jeder beliebigen Bauweise mit denen von Bauweisen nach RStO vergleichen. Als Ergebnis kann festgehalten werden, dass das Sicherheitsniveau einer bestimmten Bauweise nach RStO genauso groß ist, wie eine Befestigung mit einer dünneren Asphalttragschicht, dafür jedoch einer steiferen ToB
The aim of this thesis was the extension of the knowledge about the resilient stress-deformation behaviour of unbound granular materials (UGM). Due to difficulties in modelling the behaviour of the single materials an analytical design method does not exist at present. Therefore this thesis makes a contribution for developing such a design method. A study of international publications about the current knowledge of the stress-deformation behaviour of UGM and repeated load triaxial tests, which have been performed at Nottingham University, were the base for all further investigations. With the shakedown concept it could be shown that materials behave in a different manner depending on the applied stress level and that material laws for describing the resilient deformation behaviour of UGM have to be formulated separately for different stress ranges. Within this thesis a method is introduced which helps to find boarders for the applicability of different material laws and limiting stress lines where below the lines stable behaviour and admissible deformations for the material are expected. Applying selected material laws finite element calculations have been performed. Comparing calculation results with measurement results it can be shown that the Dresden model offers the best approach. Calculations for pavement constructions applying the Dresden model have resulted that the vertical stresses differ very much in comparison with elastic behaviour for the UGM. It can be concluded that the thickness of the covering bounded layers have an effect to the contribution of the unbound granular layers at the complete deformation behaviour of the pavement construction. Finishing a method is introduced to determine the safety levels of pavement constructions. It seems to be possible to compare the stress-strain levels of any pavement construction with those from the german standard RStO 01. Existing functions could be modified to determine safety coefficients, i. e. ratios between admissible and existing numbers of load cycles. It can be concluded that there are the same safety levels for different pavement constructions ? a thinner asphalt layer can be compensated with a stiffer UGM

Style APA, Harvard, Vancouver, ISO itp.

34

Jarmolajeva, Ela. "Lenkiamų plokščių optimizacija prisitaikomumo sąlygomis". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2007. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2007~D_20070703.093114-40459.

Pełny tekst źródła

Streszczenie:

Disertaciniame darbe, pasitelkus deformuojamo kūno mechanikos energinius principus ir matematinio programavimo teoriją, iš vieningų pozicijų išnagrinėtos tiek tamprių, tiek tamprių-plastinių sistemų deformacijų darnos (Sen-Venano) lygtys. Sprendžiant energinio principo apie papildomos energijos minimumą pagrindu sudarytą ekstremumo analizės uždavinį, įrodoma, kad yra tik trys nepriklausomos Sen-Venano lygtys su atitinkamai performuotomis kraštinėmis sąlygomis. Prisitaikomumo teorija nagrinėja tamprių-plastinių konstrukcijų, veikiamų kintamos-kartotinės apkrovos, būvį, pasitelkdama tiek tamprumo, tiek plastiškumo teorijų pagrindines lygtis ir priklausomybes: disertaciniame darbe pavyko, pasinaudojant Kuno ir Takerio optimalumo sąlygomis, metodiškai pagrįstai įjungti į plastinį konstrukcijų skaičiavimą liekamųjų deformacijų darnos lygtis. Taigi, disertacijoje Kuno ir Takerio sąlygos originaliai pritaikytos tamprumo teorijos lygtims įtempiais ir asociatyvinio tekėjimo dėsnio išraiškoms plastiškumo teorijoje gauti. Pasinaudojant gautaisiais rezultatais patobulinta prisitaikančių lenkiamų plokščių optimizavimo teorija ir sukurti nauji tokių uždavinių sprendimo metodai. Netiesinių uždavinių matematiniai modeliai, sudaryti taikant pusiausvirų baigtinių elementų metodą, sprendžiami iteraciniu būdu, pasitelkus Rozeno projektuojamųjų gradientų algoritmą. Darbui būdinga tai, kad matematinio programavimo teorija optimizavimo problemos nagrinėjimą lydi nuo matematinio modelio sudarymo iki... [toliau žr. visą tekstą]
Adapted perfectly elastic-plastic structure satisfies strength conditions and it is safe with respect to cyclic-plastic collapse. But it can do not satisfy its serviceability requirements, for instance, stiffness ones. Therefore, not only strength, but also stiffness conditions-constraints should be included in the discrete mathematical models of bending plate parameter or load variation bound optimization problems (exactly such problems are considered in the dissertation). Using mathematical programming not only new optimization technique of bending plates at shakedown is developed, but also relation between Kuhn-Tucker conditions and strain compatibility (Saint-Venant) equations and dependences of associative yield law of the deformable body mechanics is showed in the dissertation. Mathematical models of nonlinear problems are constructed applying method of equilibrium elements and are solved by iterations using Rosen project gradient algorithm. The feature of this research work is that the theory of mathematical programming accompanies investigation of optimization problem from the construction of the mathematical model up to its numerical solution, at the same time revealing mechanical meaning optimality criterion of applied Rosen algorithm.

Style APA, Harvard, Vancouver, ISO itp.

35

Wetter, Robbin [Verfasser], Valentin L. [Akademischer Betreuer] Popov, Valentin L. [Gutachter] Popov, Manfred [Gutachter] Zehn i Alexander [Gutachter] Filippov. "The interplay of system dynamics and dry friction: shakedown, ratcheting and micro-walking / Robbin Wetter ; Gutachter: Valentin L. Popov, Manfred Zehn, Alexander Filippov ; Betreuer: Valentin L. Popov". Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156181550/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

36

Blaževičius, Gediminas. "Strypų konstrukcijų prisitaikomumo analizė inkrementiniu-iteratyviniu metodu". Master's thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110617_190757-56397.

Pełny tekst źródła

Streszczenie:

Darbo tikslas – tampriųjų-plastinių strypų konstrukcijų (santvaros, rėmų), veikiamų kartotinės kintamosios apkrovos, prisitaikomumo proceso ir būvio įtempių ir deformacijų analizė optimalaus konstrukcijų projektavimo kontekste. Darbo aktualumas grindžiamas prisitaikančių konstrukcijų optimizavimo uždaviniuose figūruojančių standumo sąlygų-apribojimų kokybės gerinimo būtinumu. Prisitaikančių konstrukcijų deformacijų būvis priklauso nuo apkrovimo istorijos, o poslinkių ribojimui taikoma nepakankamai tiksli Koiterio sąlyga arba liekamųjų poslinkių influentinė matrica, nepagrįstai laikant, kad plastinio deformavimo procesas yra išimtinai holonominis. Anotuojamame darbe apkrovimo istoriją siūloma įvertinti, atliekant papildomą inkrementinę deformacijų būvio analizę. Tyrimai atlikti taikant idealiai tamprių plastinių santvarų ir rėmų techniškosios skaičiavimo teorijos prielaidas (maži poslinkiai ir deformacijos). Taikomi ekstreminiai energiniai mechanikos principai, matematinio programavimo teorija ir metodai. Inkrementinės analizės matematiniai modeliai sudaryti, besikeičiančias plastines deformacijas tapatinant su distorsijomis. Taip nustatomos konkrečios apkrovimo istorijos liekamųjų poslinkių kitimo maksimalios ir minimalios reikšmės. Gautieji rezultatai panaudoti optimizavimo uždavinių sprendiniams tikslinti ir, esant būtinumui, leidžiantys keisti pradines pagrindinio optimizavimo uždavinio sąlygas. Pateikti išsamūs skaitinių eksperimentų rezultatai.
The purpose of this work is analysis of stress-deformation state of perfectly elastic-plastic shakedown structures (truss, frames) subjected to repeated variable load in the context of optimal design. Relevance of this work is based on a need of improvement of accurateness of stiffness constrains in optimization problems of structures. Stress-deformation state of shakedown structures depends on its loading history, while for the restriction of displacements inaccurate Koiter’s condition or an influence matrix of residual displacements, on the wrong supposition that the process of plastic deformation is exclusively holonomic, is used. In this work is proposed to evaluate loading history by performing an additional incremental analysis of stress-deformation state. This research was performed invoking the assumptions of technical computing theory of perfectly elastic-plastic trusses and frames (small deformations and displacements). Mechanics extremum energy principles, mathematical programming theory and methods are applied. Mathematical models of incremental analysis are composed by indentifying volatile plastic deformations with distortions. Thus particular maximum and minimum values of residual displacements are found. Obtained results are used to verify optimal design problems solutions and change the restrictions of main optimimization problem if necessary. Comprehensive results of numerical experiments presented.

Style APA, Harvard, Vancouver, ISO itp.

37

Bowman, April Joy. "Performance of silty sands and their use in flexible airfield pavement design". Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/287462.

Pełny tekst źródła

Streszczenie:

Traditionally, flexible pavement design relies on past experience and semi-empirical methods developed through a combination of element testing and modelling. Element testing in this area especially, has centred on the performance of clean sands. This is in conflict with actual practice where a wide range of fines and soil gradations could be present in a real-world project. This research investigates the characteristics of natural sands and examines the influence of these marginal materials in pavement design using element testing and controlled modelling of an actual flexible pavement system. The element tests concentrated on separate, natural soils sourced from Kazakhstan which had similar mineralogy, but varying amounts of fines. One of the key parameters examined was equivalent void ratio and its efficiency to account for the behaviour change in granular materials which comes from increased fines content. Starting with monotonic triaxial results combined with strength-dilatancy methods it was shown that prediction of shear strength in a silty-sand could be improved by 13%. Incorporating this finding into repeat load triaxial tests, the transitions between elastic, plastic, and ratcheting failure behaviours (i.e. shakedown boundaries), commonly used to help predict the lifespan of a flexible pavement, were examined. It was seen that cycling a silty-sand, the stress path and yield surface could change depending on the fines content. The Cambridge Airfield Pavement Tester (APT) was designed and constructed to measure permanent subgrade deformation resulting from various surface loads. The number of input variables required to design flexible pavements is one of the most frequently stated problems in the field; variation of aircraft types, environmental conditions, and materials makes mechanistic design of the soil foundation problematic. Accordingly physical pavement modelling continues to be the only experimental method that allows input parameters and material characteristics to be examined simultaneously. Digital image correlation (DIC) was incorporated into the system; the first time this technology has been used in flexible pavement research. A Null Pressure System was also installed to measure soil stress distributions. It was observed that the critical failure mechanisms for thin and thick surficial layers are different, resulting in changes in the rates of surface rutting. Finally, by combining element and APT results, knowledge of the causal relationships between subsurface deformation and failure mechanisms in flexible pavement were advanced. In-situ soils, which are frequently incorporated into subgrade designs, were found to have a substantial role in the serviceability of the pavement. Correlations between element tests and APT results highlighted the complicated loading and boundary conditions present in a pavement.

Style APA, Harvard, Vancouver, ISO itp.

38

Flicek, Robert C. "Analysis of complete contacts subject to fatigue". Thesis, University of Oxford, 2015. http://ora.ox.ac.uk/objects/uuid:10c6e429-4e9e-45f0-a7a6-21823592043b.

Pełny tekst źródła

Streszczenie:

Engineering assemblies are very frequently subject to fretting fatigue, which is a damage process that results when very small slip displacements arise at nominally stationary frictional interfaces. Fretting accelerates the initiation and early propagation of fatigue cracks, thereby causing significant reductions in the fatigue performance of many critical engineering components. A majority of the previous research on fretting fatigue has focused on incomplete (i.e. smooth-edged) contacts, while complete (i.e. sharp-edged) contacts have received less attention. The aim of this thesis is to contribute to the theoretical understanding of complete contacts, especially when they are subject to fatigue conditions. This problem is addressed in two separate ways. First, because fretting failures almost invariably initiate from the edge of contact, a detailed understanding of the conditions in this region should enable more accurate assessments of fatigue performance to be made. Thus, an asymptotic analysis is presented, which provides an accurate description of the contact edge under many conditions. This is done by using the elasticity solution for a semi-infinite notch to represent the state of stress near the contact edge in an asymptotic sense. Attention is then placed on the fact that cyclically loaded frictional contacts tend toward a steady-state response in which less frictional slip (and energy dissipation) occurs than in the first few load cycles. To investigate this effect, a numerical sub-structuring procedure is described, which significantly reduces the number of degrees of freedom in finite element models of frictional contact. This reduced model is then used to calculate the shakedown limit, i.e. the amplitude of cyclic load above which frictional slip is guaranteed to persist in the steady state. The sensitivity of the steady-state solution to the initial residual displacement state is then investigated, and it is shown that initial conditions can have a large influence on the steady-state behaviour of complete contacts.

Style APA, Harvard, Vancouver, ISO itp.

39

Venskus, Artūras. "Prisitaikančių konstrukcijų optimizavimas. Sąsajos su projektavimo standartais". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2011~D_20110623_163527-78022.

Pełny tekst źródła

Streszczenie:

Disertaciniame darbe išplėtota vieninga tamprių-plastinių prisitaikančių sistemų optimizavimo su stiprumo, standumo ir klumpamosios galios sąlygomis, taikant ekstreminius energinius principus, matematinio programavimo teoriją, šiuolaikines kompiuterines technologijas ir sąsajas su projektavimo standartais, metodika. Darbe parodyta, kad prisitaikomumo teorija yra bendriausias metodinis įrankis skirtas statybinių konstrukcijų skaičiavimui nuo įvairių apkrovų, įgalinantis išvengti detalios apkrovimo istorijos nagrinėjimo. Disertaciją sudaro įvadas, penkeri skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai ir keturi priedai. Įvadiniame skyriuje aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimų objektas, formuluojamas darbo tikslas bei uždaviniai, aprašoma tyrimų metodika, darbo mokslinis naujumas, darbo rezultatų praktinė reikšmė, ginamieji teiginiai. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimų konferencijose sąrašas bei disertacijos struktūra. Pirmasis skyrius skirtas literatūros apžvalgai. Jame atlikta prisitaikančių konstrukcijų optimizavimo metodų apžvalga, išryškinta būtinybė pasitelkti sąsajas tarp teorinių optimizavimo metodų ir projektavimo standartų. Antrajame skyriuje aptariama konstrukcijų diskretizacija, sudaryti patobulinti projektinio ir patikrinamojo uždavinių matematiniai modeliai. Trečiajame skyriuje parodyta sąsaja tarp statybos inžinerijoje... [toliau žr. visą tekstą]
The optimization methodology of shakedow structures evaluating strength, stiffness and stability constraints and unifying extremum energy principles, mathematical programming theory, stat-of-the-art computer technologies and design standards was developed in the dissertation. There are shown in the work that shakedown theory is a generalized tool for calculation of civil engineering structures under different loading conditions that avoid detailed investigation of loading history. The dissertation consists of six parts including Introduction, 5 chapters, Conclusions, References and 4 Annexes. The introduction reveals the investigated problem, importance of the thesis and the object of research and describes the purpose and tasks of the paper, research methodology, scientific novelty, the practical significance of results examined in the paper and defended statements. The introduction ends in presenting the author’s publications on the subject of the defended dissertation, offering the material of made presentations in conferences and defining the structure of the dissertation. Chapter 1 revises used literature. The optimization methods of shakedown structures are reviewed and a demand of linkage between theoretical optimization methods and standards is highlighted. Chapter 2 describes the discretization of structures, the mathematical models for improved design and check problems was created. In the Chapter 3 the equivalence between load combinations of civil engineering... [to full text]

Style APA, Harvard, Vancouver, ISO itp.

40

Levy, Nina Hannah. "Modelling multi-directional behaviour of piles using energy principles". University of Western Australia. Dept. of Civil and Resource Engineering, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0211.

Pełny tekst źródła

Streszczenie:

The loads applied to pile foundations installed offshore vary greatly from those encountered onshore, with more substantial lateral and torsional loads. For combined axial and lateral loading the current design practice involves applying an axial load to a deep foundation and assessing the pile behaviour and then considering a lateral load separately. For the problem of an altering directions of lateral loads (e.g. due to changes in the wind directions acting on offshore wind turbines) a clear design procedure is not available. There is thus a need for a clearly established methodology to effectively introduce the interaction between the four different loading directions (two lateral, one axial and one torsional). In this thesis, a model is presented that introduces a series of Winkler elasto-plastic elements coupled between the different directions via local interaction yield surfaces along the pile. The energy based method that is used allows the soil-pile system to be defined explicitly using two equations: the energy potential and the dissipation potential. One of the most interesting applications of this model is to piles subjected to a change in lateral loading direction, where the loading history can significantly influence the pile behaviour. This effect was verified by a series of experimental tests, undertaken using the Geotechnical Centrifuge at UWA. The same theory was then applied to cyclic loading in two dimensions, leading to some very useful conclusions regarding shakedown behaviour. A theoretically based relationship was applied to the local yielding behaviour for a pile subjected to a combination of lateral and axial loading, allowing predictions to be made of the influence of load inclination on the pile behaviour. The ability of this model to represent interaction between four degrees of freedom allows a more realistic approach to be taken to this problem than that considered in current design practice.

Style APA, Harvard, Vancouver, ISO itp.

41

Pasten, Cesar. "Geomaterials subjected to repetitive loading: implications on energy systems". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47740.

Pełny tekst źródła

Streszczenie:

Improvements in quality of life, population growth, and environmental restrictions associated with the burning of fossil fuels will accentuate the need for renewable energy and energy geo-storage. A salient characteristic of these systems is that they impose numerous cycles of effective stress, temperature, and humidity on the surrounding geomaterials. This thesis quantifies future energy consumption based on realizable scenarios and explores the behavior of geomaterials subjected to mechanical and thermal cycles in view of energy-related applications. The long-term behavior of geotechnical systems subjected to a large number of mechanical load cycles is studied with a new numerical scheme based on a hybrid finite element formulation. The numerical scheme satisfies initial conditions as well as fundamental characteristics of soil behavior, such as threshold strain, terminal density, and long-term ratcheting. Numerical results show that shallow foundations subjected to repetitive loading experience strain accumulation and stress redistribution. On the other hand, the long-term behavior of energy piles, exposed geomembranes on slopes, and jointed rock masses subjected to cyclic thermal changes is studied using a combination of numerical, analytical, and experimental methods. Results show that thermal cycles lead to the gradual accumulation of plastic displacements, which may be amplified by thermally-induced wedging in jointed rock masses. In general, cumulative effects caused by repetitive loads increase with the number of cycles, the static factor of safety, the amplitude of the cyclic excitation, and the magnitude of the cyclically-induced displacement with respect to the critical elastic displacement.

Style APA, Harvard, Vancouver, ISO itp.

42

Lautrou, Nicolas. "Amorçage de fissure de fatigue dans un joint soudé de type naval : étude expérimentale et numérique". Université de Bretagne occidentale, 2007. http://www.theses.fr/2007BRES2051.

Pełny tekst źródła

Streszczenie:

Ce travail porte sur l'étude du comportement en fatigue d'assemblages soudés en acier S355NL, représentatifs d'éléments de structures navales. L'objectif est de développer une méthodologie pour estimer la durée de vie à l'amorçage d'une fissure de fatigue pour ce type de structures. L'approche proposée se décompose en deux étapes. Premièrement, un calcul de structure par éléments finis permet d'obtenir les cycles contraintedéformation stabilisés en tout point de l'assemblage soudé pour un chargement d'amplitude constante ou variable. Ce calcul prend en compte le comportement élastoplastique du métal de base, une variation de la limite d'élasticité dans la soudure basée sur des mesures de dureté, la géométrie locale du pied de cordon mesurée sur des photos de profil des éprouvettes, et éventuellement la présence de contraintes résiduelles. Deuxièmement, dans le cas où une adaptation élastique rapide se produit, un post-traitement permet de calculer la durée de vie à l'amorçage d'une fissure de fatigue, par l'utilisation d'un modèle d'endommagement à deux échelles basé sur les travaux de Lemaitre et al. . Les paramètres matériaux de ce modèle ont été identifiés à partir de courbes d'endurance établies pour le métal de base. Pour valider l'approche proposée, des essais de fatigue en flexion quatre points ont été réalisés sur des éprouvettes soudées réalisées par DCNS. Pour compléter l'analyse, des mesures de contraintes résiduelles présentes dans les éprouvettes soudées ont été réalisées par diffraction de rayons X. Les comparaisons entre les durées de vie expérimentales et les durées de vie calculées sont encourageantes pour la campagne d'essais réalisée.

Style APA, Harvard, Vancouver, ISO itp.

43

Jing, Peng. "Etude de l'effet des fines et de la teneur en eau sur le comportement hydromécanique des matériaux granulaires". Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAD008/document.

Pełny tekst źródła

Streszczenie:

Les matériaux granulaires sont souvent utilisés dans les chaussées à faible trafic, pour la réalisation des couches d'assise non liées. L'objectif de la thèse est une meilleure compréhension du comportement hydromécanique des matériaux granulaires insaturés sous charge répétée en tenant compte des différents effets couplés: teneur en eau et teneur en fines. Une série d'essais triaxiaux à chargements répétés (TCR) est réalisée avec les différents échantillons de sable de Missillac remodelés à différentes teneurs en eau et en fines pour caractériser les comportements de déformation permanent et résilient. En outre, les courbes de rétention sont obtenues par des essais de succion. Puis, sur la base des résultats expérimentaux, les modèles de déformations permanentes et réversibles existants sont améliorés pour prendre en compte les teneurs en fines et en eau variables. Finalement, le comportement de l'état limite du sable Missillac est estimé avec les effets des teneurs en fines et en eau
Granular materials are often used in low traffic pavement structures as unbound granular base and sub-base layers. The objective of this context is a better understanding of hydromechanical behaviour (deformation behaviour mainly) of the unsaturated granular materials under repeated loading taking into account the various coupled effects: water content and fine content. A series of RLTTs are conducted with the different remolded Missillac sand samples at different water contents and fine contents to characterize the permanent and resilient deformation behaviour. Besides, the soil water retention curves (SWRCs) are obtained by suction measurement. Then, based on the experimental results, the existing permanent and resilient deformation models are improved to accommodate to the changeable fine content and water content. In the end, the shakedown behaviour of Missillac sand is estimated with the effects of fine content and water content

Style APA, Harvard, Vancouver, ISO itp.

44

Li, Jing-Shin, i 李璟鑫. "Shakedown Analysis Based on a Primal-Dual Method". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/21652234588308574831.

Pełny tekst źródła

Streszczenie:

碩士
中華科技大學
飛機系統工程研究所
102
The thesis aims to investigate shakedown analysis of framed structures and truss structures by a primal-dual method. Shakedown analysis is a direct method to evaluate the load carrying capacity of a structure subjected to variable cyclic loads. The direct method is an effective tool for structure optimal design and safety evaluation. By the static or kinematic shakedown theorem, we can formulate the shakedown analysis problem as an optimization problem. In the thesis, we illustrate the duality relationship between the lower and upper bound formulations analytically by the Hölder inequality and numerically by the primal and dual analysis, respectively. Accordingly we can solve simultaneously lower bound problem and upper bound problem by a primal-dual method. The primal-dual algorithm provided by MATLAB is adopted to perform the shakedown analysis of framed structures and truss structures, respectively. For comparisons and validations, elastic-plastic analysis is also conducted by the commercial finite-element code ABAQUS. Finally, comparisons with good agreement validate the numerical results presented in the paper.

Style APA, Harvard, Vancouver, ISO itp.

45

Meier, Gerhard [Verfasser]. "Numerische und experimentelle Shakedown-Untersuchungen an Druckbehälterstutzen / Gerhard Meier". 2005. http://d-nb.info/978144287/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

46

Dai, Ren-Cing, i 戴仁清. "Analysis of Plastic Limit Load and Shakedown Limit Load by ABAQUS". Thesis, 2014. http://ndltd.ncl.edu.tw/handle/15093538337647967153.

Pełny tekst źródła

Streszczenie:

碩士
中華科技大學
飛機系統工程研究所
102
The thesis investigates plastic limit load and shakedown limit load of truss structures and square plates with single central circular hole by ABAQUS. The capabilities of step-by-step elastic-plastic analysis and direct cycle analysis in ABAQUS are adopted to perform the numerical computations. Unlike the step-by-step elastic-plastic analysis, the approach of direct cyclic analysis avoids considerable numerical expense with only one loading cycle prescribed. For comparisons, the computing tool MATLAB is also adopted to perform the primal-dual analysis. As shown in illustrative examples, the results obtained by ABAQUS agree very well with those acquired by MATLAB. The physical phenomena are investigated corresponding to plastic limit load and shakedown limit load of truss structures and square plates with single central circular hole. In addition, future applications of results acquired in the thesis are also discussed.

Style APA, Harvard, Vancouver, ISO itp.

47

Xing, Li-Xue, i 邢立學. "A Study of Plastic and Shakedown Limit Surfaces in Load Space". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/pgrbq3.

Pełny tekst źródła

Streszczenie:

碩士
國立臺灣大學
土木工程學研究所
105
In design of civil structures, most regulatory codes have adopted limit design specifications; hence, the development of analysis methods --- limit analysis --- to match the limit design is a very important issue. A significant feature of plasticity is ``path to path", and the relationship between displacement and load is ``path-related". In general, there is an ``initial yield surface" before the material is first yielded. With the loading of the force, the material is switched to the plastic stage. With the different load paths, it will evolve into different sequences of subsequent yield surfaces; that is, the evolution of the yield surface is not unique and depends upon the paths. However, there exists a unique ``plastic limit surface" in the load space which demarcates the safe loads and the static collapses; that is to say, it is not necessary to carry out a complicated plastic time history analysis. If the load is cyclically repeated, then plastic deformation either may result in vicious incremental collapse or alternating yield (plastic fatigue) phenomena, or may result in such appropriate residual stress distributions as shakedown phenomena occur. Between the safe cyclic loads and the incremental collapse or alternating yield, it is possible to establish a unique "shakedown limit surface" in the load space without the need for a complicated cyclic plastic time history analysis. In this thesis, we discuss the calculation method of the plastic limit surface and the shakedown limit surface in the load space. By using the linearly elastic-perfectly plastic model, we construct the vector inequality and then extend the linear algebra calculation method to the inequality calculation. By skipping the calculation of the subsequent yield surfaces, we can directly calculate the collapse modes, and then obtain the plastic limit surface (static collapse) and the shakedown limit surface (incremental collapse and alternating yield). The developed calculation method, applicable to trusses, beams and rigid plane frames, is verified by examples taken from the existing literature.

Style APA, Harvard, Vancouver, ISO itp.

48

TSAO, YOU-CHENG, i 曹佑誠. "Shakedown Limit Load Analysis of Trusses with Non-Linear Kinematic Hardening". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/32163260366975446548.

Pełny tekst źródła

Streszczenie:

碩士
中華科技大學
航空機械系飛機系統工程碩士班
103
This thesis investigates elastic shakedown limit loads and elastic-plastic analysis of structures subjected to cyclic loads made of nonlinear kinematic hardening materials. In the thesis, the step-by-step analysis of the computer code ABAQUS is applied to consider elastic-perfectly plastic and kinematic hardening materials, respectively. Parametric studies are made to study the prediction of shakedown limit loads and the relationship between shakedown limit loads and plastic limit loads. Also, validations and comparisons are made between the results obtained by ABAQUS and MATALB. Moreover, Armstrong-Frederick and Chaboche kinematic hardening models are utilized in the related parametric studies

Style APA, Harvard, Vancouver, ISO itp.

49

[Verfasser], Thanh Ngọc Trân. "Limit and shakedown analysis of plates and shells including uncertainties / von Thanh Ngọc Trân". 2008. http://d-nb.info/990089738/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

50

Kim, Byoung Yoon [Verfasser]. "Shakedown analysis of fiber-reinforced metal matrix composite under fusion-relevant thermomechanical loading / Byoung Yoon Kim". 2005. http://d-nb.info/977657086/34.

Pełny tekst źródła

Style APA, Harvard, Vancouver, ISO itp.

Rozprawy doktorskie na temat „Shakedown”

Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych