Rozprawy doktorskie na temat „Plastic bearability of plates”

The subject of this thesis is analysis of the plastic bearability of plates. The first part is dedicated to a description of pertinent theories. It is primarily a theory of material nonlinearity and plasticity, including a description of plasticity models, which are commonly used in engineering analysis. Next is the hinted theory of geometric nonlinearity and discusses the key principles of limit plastic bearability of plates. This thesis includes ultimate strength calculations of plates of selected shapes, their solution by both, a manual calculation and using computational software. The obtained values are subsequently evaluated. The appendices contain the procedures for modelling in the computational programs RFEM and ANSYS.

The theory of buckling strength of compression members in the plastic range has been extensively studied, and numerical methods already exist which deal with such behaviour. However, there is a significant research interest in developing analytical models for the plastic buckling, largely driven by the need for simplified mechanics based design tools, but also by the desire for enhanced understanding of this complex phenomenon. A thorough investigation into the inelastic buckling of columns and plates reveals the existence of two well-known inconsistencies recognised as the 'Column Paradox' and the 'Plate Plastic Buckling Paradox'. In the current research, addressing the conceptual issues related to the plastic buckling of columns and plates, including the two associated paradoxes, has been achieved by means of development and application of analytical models that are verified against nonlinear finite element analysis. These models are based on sound principles of structural mechanics and are intended to illustrate the mechanics of the plastic buckling response of stocky columns/plates by means of a simplified analytical approach, from the point of buckling initiation and considering the post-buckling response. In these models, the Rotational Spring Analogy is used for formulating the geometric stiffness matrix, whereas the material stiffness matrix is obtained with due consideration for the spread of material plasticity. It is shown that the buckling of stocky perfect columns starts at the Engesser load while the von Karman upper limit is typically not realised due to tensile yielding at the outer fibre of the column cross-section. Furthermore, it is established that beyond a threshold level of imperfection, as evaluated directly from the developed model, the plastic post-buckling response of columns is barely affected by a further increase in the out-of-straightness. Besides identifying previous misconceptions in the research literature, the proposed analytical models for the plastic buckling of plates have proven to offer valuable insight into factors that influence the plastic buckling of stocky plates, and hence succeeded in resolving the long-standing paradox. It is the major contention of this thesis, verified through extensive studies, that the 'Plate Plastic Buckling Paradox' is resolved with the correct application of plasticity theory, considering not only the influence of initial imperfections but also the interaction between flexural and planar actions.

The strength and behavior of gusset plates in buckling is evaluated herein based on data from the experimental investigations conducted by other researchers and the analytical work presented herein. A set of design guidelines has been recommended through the review of the current practice. Representative single and double brace gusset plates normally adopted for connections with compressive bracing/diagonal members in braced frames and trusses, were modeled and analyzed using linear and nonlinear finite element methods to determine the buckling loads. The buckling analysis data along with the test data indicated the occurrence of inelastic buckling of the gusset plates. Current design practice and a set of formulas for determination of gusset plate thickness have been reviewed. A set of guidelines has been recommended for the design and evaluating gusset plate buckling loads.

This study investigates the feasibility of strengthening reinforced concrete beams with epoxy-bonded Glass-Fiber-Reinforced-Plastic (GFRP) plates. The composite plate is epoxy-bonded to the tension flange of the beam to increase its stiffness and strength. Seven rectangular and one T-beam, retrofitted with composite plates, were tested to failure under symmetrical 4-point bending. The load versus deflection and the load versus strain in the composite plate, steel rebar and the extreme compression fiber of concrete were measured and plotted for the midspan section throughout the entire range of loading up to failure. Analytical models based on the equilibrium of forces and compatibility of deformations were developed to predict the stresses and deformations of the beam in the linear and nonlinear regions. The predicted and measured results correlated well. The analytical models were used in a parametric study to investigate the effects of design variables such as, plate area, plate strength and stiffness, reinforcement ratio, etc., on the moment-curvature relationships of typical rectangular and T cross sections.

The thesis deals with the plastic bifurcation buckling of a full circular plate partially or fully bonded to an elastic foundation, and subjected to a uniform radial pressure at the periphery. The prebuckling state of stress in the plate is therefore a constant equibiaxial stress. Under this stress, the plate material undergoes strain-hardening, obeying an isotropically expanding J2 (von Mises) yield surface. The incremental constitutive relations, needed for the bifurcation analysis, are written in a way so as to incorporate behaviours according to both the J2 deformation and J2 -incremental theories of plasticity, and also to include the elastic theory. The governing equation and boundary conditions, suitable for non-axisymmetric or axisymmetric buckling, are derived using the principle of virtual work and Shanley's concept of bifurcation under increasing load. Exact analysis solves the fourth order partial differential equation, and obtains the buckling stresses for plates fixed and simply supported at the periphery, as a function of the radius to thickness ratio, and for various values of the foundation modulus.Four cases of foundation support are considered: (1) no foundation, (2) full foundation, (3) partial inside foundation for half the plate radius, and (4) partial outside foundation from half to the full radius. This is done for fixed as well as simply supported plates. Buckling stresses and the associated mode shapes, whether axisymmetric or nonaxisymmetric, are obtained for the investigated cases.Numerical results are presented for the bifurcation stress of Aluminum 24S-T3 plates and foam like foundation materials. The results show that the effect of foundation is less significant in the plastic range than in the elastic range. As expected, the buckling stresses for the incremental theory are always higher than the results for the deformation theory. For fixed plates the maximum difference is around 10% at the high end of the validity of the stress-strain curve. But, surprisingly for the simply supported plates, the results from the incremental theory are higher by less than 1%. This means, that for circular simply supported plates, the well-known plastic buckling paradox almost disappears, even in the presence of a foundation.
Cette thèse traite du voilement plastique par bifurcation d'une plate circulaire qui est partiellement ou complètement liée à une fondation élastique, et qui est soumise à une pression radiale uniforme sur sa périphérie. Avant le voilement, la plaque se trouve dans un état de contraintes équibiaxiales constantes. Sous ces contraintes, le matériau de la plaque subit un écrouissage suivant une surface de plastification en expansion isotrope J2 (von Mises). Les lois constitutives incrémentales, requises pour l'analyse de bifurcation, sont écrites de façon à incorporer le comportement selon la théorie de déformation J2, les théories incrémentales de la plasticité J2 et la théorie élastique. L'équation régissant le comportement de la plaque et les conditions frontières, adaptés au voilement axisymétrique et non-axisymétrique, sont dérivés selon le principe du travail virtuel et le principe de bifurcation sous augmentation de charge de Shanley. L'analyse exacte de l'équation différentielle du 4e degré permet d'obtenir, en fonction du ratio rayon/épaisseur des plaques et du module de fondation, les contraintes de voilement pour les plaques encastrées et simplement supportées en leur périphérie.Quatre configurations de fondations sont considérées : (1) aucune fondation présente, (2) une fondation présente partout, (3) une fondation partielle présente uniquement à l'intérieur de la moitié du rayon de la plaque et (4) une fondation partielle présente à partir de la moitié du rayon jusqu'au bord de la plaque. Ces configurations sont appliquées pour des plaques simplement supportées et encastrées en périphérie. Les contraintes de voilement ainsi que les modes de déformations associés, qu'ils soient axisymétrique ou non-axisymétrique, sont obtenus pour chaque cas.L'analyse numérique présente des résultats de contraintes de bifurcation pour des plaques d'aluminium 24S-T3 et des matériaux de fondation peu rigides de type mousse synthétique. Il en ressort que l'effet de la fondation sur les contraintes de voilement est moins important dans le domaine plastique que dans le domaine élastique. Tel que prévu, les contraintes de voilement découlant de la théorie incrémentale de la plasticité J2 sont toujours supérieurs que celles basées sur la théorie de déformation J2. Pour les plaques encastrées, à l'extrémité de la courbe contrainte-déformation, la différence maximale est d'environ 10%. Étonnamment par contre, pour les plaques simplement supportées, les résultats de la théorie incrémentale de la plasticité sont plus importants par moins de 1%. Ceci veut dire que, pour les plaques simplement supportées, le paradoxe du voilement plastique ne s'applique pas et ce, même en présence d'une fondation.

A solution procedure based on the finite strip method is presented herein, for the analysis of plate systems exhibiting geometric and material non-linearities. Special emphasis is given to the particular problem of rectangular plates with stiffeners running in a direction parallel to one side of the plate. The finite strip method is selected for the analysis as the geometry of the problem is well suited for the application of this method and also as the problem is too complicated to solve analytically. Large deflection effects are included in the present study, by taking first, order non-linearities in strain-displacement relations into account. Material non-linearities are handled by following von-Mises yield criterion and associated flow rule. A bi-linear stress-strain relationship is assumed for the plate material, if tested under uniaxial conditions. Numerical integration of virtual work equations is performed by employing Gauss quadrature. The number of integration points required in a given direction is determined either by observing the individual terms to be integrated or by previous experience. The final set of non-linear equations is solved via a Newton-Raphson iterative scheme, starting with the linear solution. Numerical investigations are carried out by applying the finite strip computer programme to analyse uniformly loaded rectangular and I beams with both simply supported and clamped ends. Displacements, stresses and moments along the beam are compared with analytical solutions in linear analyses and with finite element solutions in non-linear analyses. Investigations are also extended to determine the response of laterally loaded square plates with simply supported and clamped boundaries. Finally, a uniformly loaded stiffened panel is analysed and the results are compared with finite element results. It was revealed that a single mode in the strip direction was sufficient to yield engineering accuracy for design purposes, with most problems.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

The large ductile deformation response of stiffened plates subjected to blast loads is investigated and simplified methods of analysis of such response are developed. Simplification is derived from modelling stiffened plates as singly symmetric beams or as grillages thereof. These beams are further assumed to behave in a rigid, perfectly plastic manner and to have piecewise linear bending moment-axial force capacity interaction relations, otherwise known as yield curves. A blast loaded, one-way stiffened plate is modelled as a singly symmetric beam comprised of one stiffener and its tributary plating, and subjected to a uniformly distributed line load. For a stiffened plate having edges fully restrained against rotations and translations, both transverse and in-plane, use of the piecewise linear yield curve divides the response of the beam model into two distinct phases: an initial small displacement phase wherein the beam responds as a plastic hinge mechanism, and a final large displacement phase wherein the beam responds as a plastic string. If the line load is restricted to be a blast-type pulse, such response is governed by linear differential equations and so may be solved in closed form. Examples of a one-way stiffened plate subjected to various blast-type pulses demonstrate good agreement between the present rigid-plastic formulation and elastic-plastic beam finite element and finite strip solutions. The response of a one-way stiffened plate is alternatively analysed by approximating it as a sequence of instantaneous mode responses. An instantaneous mode is analogous to a normal mode of linear vibration, but because of system nonlinearity exists for only the instant and deformed configuration considered. The instantaneous mode shapes are determined by an extremum principle which maximizes the rate of change of the stiffened plate's kinetic energy. This approximate rigid-plastic response is not solved in closed form but rather by a semi-analytical time-stepping algorithm. Instantaneous mode solutions compare very well with the closed-form results. The instantaneous mode analysis is extended to the case of two-way stiffened plates, which are modelled by grillages of singly symmetric beams. For two examples of blast loaded two-way stiffened plates, instantaneous mode solutions are compared to results from super finite element analyses. In one of these examples the comparison between analyses is extremely good; in the other, although the magnitudes of displacement response differ between the analyses, the predicted durations and mechanisms of response are in agreement. Incomplete fixity of a stiffened plate's edges is accounted for in the beam and grillage models by way of rigid-plastic links connecting the beams to their rigid supports. Like the beams, these links are assumed to have piecewise linear yield curves, but with reduced bending moment and axial force capacities. The instantaneous mode solution is modified accordingly, and its results again compare well with those of beam finite element analyses. Modifications to the closed-form and instantaneous mode solutions to account for strain rate sensitivity of the panel material are presented. In the closed-form solution, such modification takes the form of an effective dynamic yield stress to be used throughout the rigid-plastic analysis. In the time-stepping instantaneous mode solution, a dynamic yield stress is calculated at each time step and used within that time step only. With these modifications in place, the responses of rate-sensitive one-way stiffened plates predicted by the present analyses once again compare well with finite element and finite strip solutions.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

In this study, the effects of edge contact-frictional force imposed by the machine heads on the distribution of stress state prior to buckling of plates are investigated. A contact-friction interface element is included in the pre-buckling analysis which considers the possibility of slip between the machine heads and the plate. All analyses are performed using the incremental theory of plasticity in which the formulations given by Ramberg-Osgood and Richard are implemented to calculate the tangent modulus. The pre-buckling stress states are used to determine the buckling stresses. In the buckling formulation of the plate, an element stiffness based on Hermitian interpolation function is included. The buckling stresses are compared with those of the test results and the closed form solutions available in the literature. The effect of edge boundary imperfections are also considered in this study.

There is a class of plate buckling problems in which buckling occurs in the presence of a constraining medium. This type of buckling has been investigated by many researchers, mainly as buckling of elastic columns and plates on elastic foundations. Analytical solutions have been obtained by assuming the foundation to provide tensile as well as compressive reaction forces. The present work differs from the previous ones in two respects. One, the foundation is assumed to be one-sided, thus providing only the compressive resistance. Two, the plates are allowed to be stressed in the plastic, strain-hardening range. Equations for determining the buckling stresses and wavelengths are obtained by solving the differential equations for simply supported and clamped long rectangular plates stressed uniformly in the longitudinal direction. The relevance and the usefulness of the obtained formulas is demonstrated by comparing the predicted results with the experimental results of other researchers on buckling of concrete filled steel box-section and HSS columns. It is shown that the theoretical buckling loads match quite closely with the experimental ones, and hence, should prove useful in formulating rules for the design of such columns.

Epoxy-bonding a composite plate to tension face, is an effective technique for repair and retrofit of reinforced concrete beams. Experiments have indicated local failure of the concrete layer between the plate and longitudinal reinforcement in retrofitted beams. This mode of failure is caused by local stress concentrations at the plate end, as well as at the flexural cracks. A method has been presented for calculating shear and normal stress concentrations at the cut-off point of the plate. Stress concentrations predicted by this method have been compared to both finite element method and experimental results. The analytical models provide closed form solutions for calculating stresses at the plate ends and can easily be incorporated in design equations. The ultimate capacity of the reinforced concrete beams strengthened by composite plates bonded to the tension face, is controlled by either compression crushing of concrete, rupture of the plate, local failure of concrete at the plate end, or debonding of the plate. These failure modes have been considered in developing design guidelines for flexural strengthening of reinforced concrete beams using fiber composite plates. Bonding composite plates (fabrics) to the web of reinforced concrete beams can increase the shear and flexural capacity of the beam. An analytical model has been developed to calculate the stress distribution in the strengthened beam, and the shear force resisted by the composite plate before cracking and also after formation of flexural cracks. Parametric study has been performed to reveal the effect of important parameters such as fiber orientation, and plate thickness. The ultimate shear capacity of reinforced concrete beams is also increased by epoxy-bonding composite plates to the side faces of the beam. Truss analogy and compression field theory have been used to determine the effect of the composite plate on the crack inclination angle and the shear capacity of reinforced concrete beams at ultimate state. The effects of important parameters such as plate thickness and fiber orientation angle on the crack inclination angle and the shear capacity of the strengthened beam have been investigated through a parametric study.

The general problem of plastic buckling of flat metal plates is a fundamental area of investigation in mechanics not only because of its intrinsic importance in the design of engineering structures, but also because it still has not been settled in a satisfying manner. Which theory of plasticity is the correct one to predict the buckling loads in the plastic range is a long-argued problem.
This thesis presents finite element analyses of plastic buckling and postbuckling behaviour of columns and plates, taking into account the presence of initial out-of-plane imperfections. The FE programs constructed by the author for this purpose are used to analyze the imperfection growth of such columns and plates under axial loading and simply supported edge conditions. The material behaviour is modeled according to both the incremental and the deformation theories of strain-hardening plasticity. The programs combine both the geometric and material nonlinearities to trace the load-deflection behaviours of these structures in prebuckling (up to the maximum load) as well as postbuckling ranges. The results of the analyses for plates show the extreme sensitivity of the incremental theory, and the relative insensitivity of the deformation theory, to the initial imperfections.
The programs are used to simulate the plastic buckling experiments on Aluminum tubes, taking into account their measured imperfections. The imperfection growth analyses demonstrate that the maximum load predictions of the incremental theory are quite close to those recorded in the experiments.

The concept of load analogy is used in the elastic and elastic-plastic analysis of isotropic circular and annular plates undergoing moderately large deflection. The effects of the nonlinear terms of lateral displacement and the plastic strains are considered as additional fictitious lateral loads, edge moments, and in-plane forces acting on the plate. The solution of an elastic or elastic-plastic Von Karman type plate is hence reduced to a set of two equivalent elastic plate problems with small displacements, namely, a plane problem in elasticity and a linear elastic plate bending problem. The method of finite element is employed to solve the plane stress problem. The large deflection solutions are then obtained by utilizing the solutions of the linear bending problems through an iterative numerical scheme. The flow theory of plasticity incorporating a Von Mises layer yield criterion and the Prandtl-Reuss associated flow rule for strain hardening materials is employed in this approach.

An inelastic material model for laminated composite plates and shells is formulated and incorporated into a finite element model that accounts for both geometric nonlinearity and transverse shear stresses. The elasto-plastic material behavior is incorporated using the flow theory of plasticity. In particular, the modified version of Hill's initial yield criterion is used in which anisotropic parameters of plasticity are introduced with isotropic strain hardening. The shear deformation is accounted for using an extension of the Sanders shell theory and the geometric nonlinearity is considered in the sense of the von Karman strains. A doubly curved isoparametric rectangular element is used to model the shell equations. The layered element approach is adopted for the treatment of plastic behavior through the thickness. A wide range of numerical examples is presented for both static and dynamic analysis to demonstrate the validity and efficiency of the present approach. The results for combined nonlinearity are also presented. The results for isotropic results are in good agreement with those available in the literature. The variety of results presented here based on realistic material properties of more commonly used advanced laminated composite plates and shells should serve as references for future investigations.
Ph. D.

Projections on flat plates have wide applications in the field of engineering. They are often used for transmitting loads between two or more parts. Although extensive investigations have been performed for many forms of loading, little information on the elastic and elastic-plastic behaviour of such components under shear loading is available. Parameters such as elastic stress, plastic stress and elastic-plastic strain concentration factors, in addition to the multiaxial elastic-plastic behaviour, are necessary in order to determine static design and fatigue life predictions for such components. In this test, the elastic and elastic-plastic behaviour of flat plates with projections subjected to axial and shear loading is investigated using finite element analysis. The effects of geometry, loading, boundary conditions and material models on the finite element prediction of stress and strain are studied. In the elastic analysis, a wide range of geometries are considered under axial and shear loading. The effect of the component restraints is also considered, using a plane stress assumption throughout the analysis. In addition, plane strain and 3 dimensional cases are compared with the plane stress results. For shear loading, the plane stress results provide a reasonable estimate for predictions using other models. However, for axial loading, an overestimate is achieved, thus providing a conservative estimate. In the elastic-plastic analysis, 6 geometries are selected in order to study the behaviour and mechanisms of the component subjected to various load cases such as axial, shear, combined axial + repeated shear and steady axial + reversed shear loading. Three simple material models with time-independent bi-linear stress-strain representations are assumed namely, elastic-perfectly-plastic, elastic-kinematic-hardening and elastic-isotropic-hardening. The stress and strain range predictions for combined loading are found to be independent of the steady axial load.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Um dos processos que mais tem se difundido na área de automação industrial é o processo de corte de chapas. Diversas máquinas de vários tamanhos têm sido desenvolvidas para o corte de inúmeros materiais como aço, alumínio, madeira, couro, pedra etc. Neste procedimento específico, têm sido utilizados os mais diversificados métodos de corte, desde facas em movimento alternativo ou rotativo, até a utilização de maçaricos, jato de água, laser ou plasma. O presente trabalho visa o desenvolvimento de uma mesa de corte de baixo custo para a automatização do processo de corte de chapas plásticas de pequenas espessuras. As aplicações para uma máquina deste tipo são máquinas são mais diversas, com destaque na utilização em fabricação de letreiros luminosos de acrílico. Em termos gerais, o protótipo aqui desenvolvido constitui-se de uma mesa com fresa, sendo movimentada em XY a partir de comandos vindos de um microcomputador. Além de movimentação no plano horizontal XY, existe um terceiro movimento de levantar e abaixar a fresa executado na direção vertical. Uma inovação examinada nesta protótipo, foi a utilização de guias lineares construídas a partir de perfis em C, de alumínio, com uma corrente neles fixada que desempenha o papel de cremalheira para converter o torque do motor em força motriz. Assim, a guia passou a ter a finalidade dupla e simultânea de guia propriamente e elemento de tração, evitando a necessidade de utilização de cabos ou correias. Assim , esta dissertação tem por objetivo descrever os principais elementos do protótipo construído e apresentar alguns resultados dos testes realizados.
One of the process that have been mostly diffused in the Field of industrial automatization is the one of plate cutting. Several engines of various sizes have been developed for the cutting of many materials such as steel, aluminium, Wood, leather, Stone etc. In thes specific procedure, the most diversified cutting methods have been used, from blades in alternating or rotatory movement to the utilization of blowtorches, water Jet, laser or plasma. The present tak´s aim is the development of a low-cost cutting table for the automatization of the processo f cutting plastic plates of low thickness. The applications for such a machine are several, highlighing its use in the manufactoring of acrylic lighted plackards. By definition, the prototype here developed consists of table with a Miller, put into motion in XY by commands coming from a microcomputer. Besides the horizontal plan XY movement, there is a third one of lifting and lowering the Miller executed in the vertical direction.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.
Includes bibliographical references (leaves 157-164).
The need for energy infrastructure has led to transportation of gases over long distances. The strength-grade of pipeline steels used for transportation of gases has been increasing to reduce the cost of the overall pipeline system. Along with higher strength, adequate fracture toughness and resistance to plastic buckling are required of pipes installed in earthquake- or frost-prone regions. To get higher strength with adequate deformability in low-alloy pipeline steels, plates for pipes are typically made today by thermo-mechanically-controlled rolling processes, which introduce strong crystallographic texture and anisotropy in the pipes. The plates are then cold-formed into pipes, which introduces further anisotropy and residual stresses in the pipe. In the current work, effects of various steps of the pipe manufacturing process, such as rolling, cold forming, etc., on residual stress, hardening moduli, plastic anisotropy, and eventually, to the buckling resistance of the pipe, are studied. Effects of various types of geometric perturbation on plastic buckling response of pipes are also studied.
(cont.) Due to the crystallographic texture and cold-forming, crystal plasticity-based constitutive models instead of Mises plasticity-based constitutive models may be better suited to model the pipe. In the current work, crystal plasticity-based material models are used to predict the buckling response of pipes. Results show that the buckling strain in uniaxial compression, predicted using a crystal plasticity-based model, is - 20% less than the one predicted using an "equivalent" Mises plasticity-based model, for a pipe with d/t ratio of 51. Further results show that variation in material properties and residual stresses caused by cold forming reduces the buckling strain by - 30%, for a pipe with d/t ratio of 51.
by Vaibhaw Vishal.
Ph.D.

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.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
This dissertation refers the research, which covers the areas of discursive semiotics, communication and fashion, having as its universe the set of Alceu Penna s fashion plates, in the magazines O Cruzeiro, within the column Figurinos, in the 1950 s decade. The corpus of this research was built out of this set of images, enabling the construction of the social practices visibility issue, referring to a certain female simulacrum and type of women, inserted in the image universe of the magazine. Thus, the research revolves around the questions: What kind of Brazilian woman simulacrum Alceu Penna proposed through O Cruzeiro magazine? How did he construct this simulacrum in the fashion drawings in the magazine? This way, the research seeks to identify and analyze the fashion images proposed by the designer as its general goal. Such images signal female features that will anchor the construction of a Brazilian woman simulacrum. For the specific goals the research seeks to achieve the following: 1) Present the female way(s) of dressing conveyed in Alceu Penna s column called Figurinos; 2) Contribute for the identification of the Brazilian woman in the 1950 s decade; 3) Verify existing conceptual relations between fashion, woman simulacrum and the culture industry represented in O Cruzeiro magazine, within the column Figurinos during that period; 4) Establish the logic in the relations between the expression categories (plastic formants) and the content categories (meaning generative course) in order to describe the type of semiosis existing between expression plan and content plan; 5) Identify correlations between the fields of fashion, advertising and economics in the magazine; 6) Contribute to fashion studies. The methodological procedures compose a descriptive and interpretative method for the analysis of verbal and visual arrangements of the text, named syncretic, which copes with the identification of mechanisms that structure internally the text in relation to the sociohistorical context. This way, the structural complexity of the text was understood, in which the relations and semiosis are produced as a whole of meaning, according to Algirdas Julien Greimas theoretical framework. Also, the sociosemiotics developed by Eric Landowski was used, highlighting the concepts of simulacrum, presence as a sense system, correlated to interaction and visibility systems. The analysis of the visual aspect of fashion plates in the column was grounded on Jean-Marie Floch s plastic and syncretic semiotics approaches. As for the visuality aspect of fashion Ana Claudia de Oliveira s statements were used, which relate it to appearance discourses. Having this accession, the semiotic analysis tested the hypothesis that Alceu Penna s fashion plates shape a slim, thin female body, with marked waist and gestures that show sometimes a relaxed, moved posture in its internal world and sometimes a formal, static and conservative one in a social environment. It was apprehended in these drawings the construction of a family woman simulacrum, who is within a dependence relation with the masculine, and a Brazilian woman simulacrum, who follows the international fashion trends and shows herself to others, besides the adoption of Brazilian culture stereotypes, in order to reveal her insertion and sense of belonging to the elites context. The drawings correlate to the advertising discourses of the magazine, that promote an economic model of consumption of goods produced by the implanted industry in the country, linked a model Brazilian social of a modern way of life, where the masculine and the feminine have support with French and New Yorker fashion matrixes
Esta dissertação refere-se à pesquisa que abrange as áreas da semiótica discursiva, comunicação e moda, tendo como universo o conjunto de imagens de moda dos figurinos de Alceu Penna inserido na coluna Figurinos da revista O Cruzeiro, da década de 1950. Deste conjunto foi extraído o corpus de pesquisa, possibilitando estudar a visibilidade das práticas sociais referentes a determinado simulacro feminino e tipo de mulher inscrito no universo imagético da revista. Sendo assim, a pesquisa gira em torno das seguintes questões: Que simulacro de mulher brasileira Alceu Penna propôs por meio da revista O Cruzeiro? Como ele construiu este simulacro nos desenhos de figurinos de moda da revista? Desta forma busca-se, como objetivo geral, identificar e analisar as imagens de moda propostas pelo figurinista que assinalam modos de presença feminina que perseguem a construção de um simulacro de mulher brasileira. Na seqüência da investigação, busca-se alcançar os seguintes objetivos específicos: 1) Apresentar o(s) modo(s) de vestir feminino(s) veiculado(s) na coluna Figurinos de Alceu Penna; 2) contribuir para identificação da mulher brasileira dos anos de 1950; 3) verificar as relações conceituais existentes entre moda, simulacro de mulher e indústria cultural representadas pela revista O Cruzeiro, que está inscrita na coluna Figurinos no período determinado; 4) estabelecer a lógica das relações existentes entre as categorias da expressão (formantes plásticos) e as categorias do conteúdo (percurso gerativo do sentido) para descrever o tipo de semiose entre plano da expressão e plano do conteúdo; 5) identificar as correlações entre seção de moda, publicidade e economia na revista; 6) contribuir para os estudos da moda. Os procedimentos metodológicos adotados configuram um método descritivo e interpretativo para a análise do arranjo visual e verbal do texto, denominado sincrético e esses dão conta da identificação dos mecanismos que estruturam internamente o texto em relação ao contexto sóciohistórico. Desta forma compreendeu-se a complexidade estrutural do texto no qual relações e semioses são produzidas em um todo de sentido segundo o referencial teórico de Algirdas Julien Greimas. Empregou-se ainda a sociossemiótica desenvolvida por Eric Landowski destacando os conceitos de simulacro e de presença, como regimes de sentido, correlatos aos regimes de interação e de visibilidade. Para analisar o aspecto mais visual do figurino na coluna, o embasamento foi a semiótica plástica e a sincrética nos desenvolvimentos de Jean-Marie Floch. E na abordagem da visualidade da moda, seguiu-se Ana Claudia de Oliveira que a relaciona a discursos da aparência. Com este aporte a análise semiótica testou as hipóteses de que os desenhos dos figurinos de Alceu Penna configuram um corpo feminino esguio, magro, com cintura demarcada, com quadril em evidência enquanto a gestualidade mostra uma postura ora descontraída e movente no interno do seu mundo, ora formal, estática e conservadora no social. Nestes desenhos depreendeu-se a construção de um simulacro de mulher da família, que está em relação de dependência com o masculino, e de um simulacro de mulher brasileira que segue a moda internacional e se mostra para o outro, através da adoção dos estereótipos da cultura brasileira, para revelar sua inserção e pertencimento no contexto das elites. Os desenhos se relacionam aos discursos publicitários da revista que promovem um modelo econômico de consumo de bens produzidos pela indústria implantada no país, aliado ao modelo social brasileiro de vida moderna, onde o masculino e o feminino se apoiam nas matrizes da moda francesa e nova iorquina

碩士
國立臺灣大學
機械工程學研究所
90
Hot embossing has excellent performance in replicating precise micro-feature into large plastic plates. It has become a popular process after the microstructure in master mold can be easily made with the LIGA and MEMS technology. Before embossing, the plastic plates must be heated above glass transition temperature. The heating is usually done with hot plates. It is time-consuming, and the core of the plates is unnecessarily softened. This study attempts to use the Ultrasonic vibration as heat generator in hot embossing. The method has been used in conventional ultrasonic welding. This paper has two objectives: (1) To measure the temperature distribution and evolution at different depth of the ultrasonic-heated plastic plates, with comparison to those heated with hot plate; (2) To study the microstructure replication capacity of the ultrasonic-heating embossing of amorphous and semi-crystalline plastic plates. Temperature measurement reveals that Ultrasonic heating provides very rapid heating of surface layer. For the system used (15kHz,28μm amplitude),the temperature reached and the time taken to reach such temperature depends on the vibration time. For the same peak temperature, Ultrasonic heating takes less than 10 seconds, while conventional hot-plate heating takes more than 120 seconds. The cooling is also faster in the plastic plates heated with ultrasound than those heated with hot plates. It is proven to be an effective heating/cooling system for hot embossing operation. The replication capacity of microstructures using ultrasonic heating is not as good as those using hot plates. But it may be due to the other processing such as pressure and vibration amplitude etc. The operation windows, defined as the range of processing on the plane of vibration time and holding pressure, for amorphous plastics are much large than those for semi-crystalline ones.

碩士
長庚大學
機械工程研究所
95
This paper reports a rapid fabrication of polymeric micro-block arrays using an IR heated hot embossing process. A pneumatically actuated embossing facility with IR heating capacity has been designed, constructed and tested in our laboratory. To mold micro-blocks onto the plastic plates, a silicon mold with an array of micro-block cavities is fabricated by photolithography and deep reactive ion etching. During the embossing process, a PMMA plate was first placed above the mold. A ceramic IR heater was placed above the PMMA plate to heat the mold. During heating, the IR passed through the transparent PMMA to reach and heat up the mold surface. After the retrieve of the IR heater, the pneumatically actuated embossing facility pressed the plastic plate against the hot master mold. A micro-block array is obtained. The effect of various processing parameters on the replicability of the micro-blocks was investigated. Under the proper processing conditions, the 50x37 arrays of polymeric micro-blocks, with a dimension of 200 m x 80 m x 40m can be successfully fabricated. The experimental results in this study suggest that IR heated embossing could provide an effective way of fabricating microstructures onto plastic plates. This would provide significant advantages in terms of a shorter cycle time as well as improved product quality.

碩士
大葉大學
機械工程研究所碩士班
96
The bipolar plate of PEMFC`s is made of graphite plate by using milling machines, which makes the cost of bipolar plates constitute a large portion of that of fuel cell stacks. Furthermore, more than 80% of the weight of a fuel cell stack comes from the bipolar plates. Although researchers in the field of fuel cells have conducted so much R＆D work relevant to the bipolar plate technology, good solutions to this problem is still yet to come. The present project proposes a novel design of bipolar plates which can be formed by injection or compression molding process using plastic materials and a current collector can be inset on its surfaces . The current collector together with the gas diffusion layer can conduct electrons easily under certain operating conditions and stack designs. The main purpose of the present project is to investigate the feasibility of applying the plastic bipolar plates in the Air-breathing PEMFC`s. We will conduct the related experiments and computer simulations to validate the application of this innovation in fuel cells. Hopefully, in the near future the plastic bipolar plates can be used to reduce the cost of fuel cells.

碩士
長庚大學
機械工程學系
98
This paper reports a novel infrared assisted roller embossing technique for the rapid fabrication of polymeric diffusion films with dual-sided microstructures. A roll-to-roll embossing facility with infrared heating has been designed, constructed and tested in our laboratory. Metallic rollers bearing microstructures are fabricated using a tungsten carbide turning machine. They were then used to replicate the microstructure onto 0.5 mm thick PC and PET films in the experiments. During roller embossing, the rollers are heated by the infrared energy to melt the thermoplastic at the roller/film interface and thereby to replicate the microstructure. Under the proper processing conditions, plastic films with 90 degree cross-angle dual-sided microstructures can be successfully fabricated. The experimental results in this study suggest that infrared assisted roller embossing provides an effective way of fabricating microstructures onto plastic substrates. This would provide significant advantages in terms of a shorter cycle time as well as improved product quality.

碩士
大葉大學
機械與自動化工程學系
98
The bipolar plates of PEMFC's are made of graphite plate by using milling machines, which makes the cost of bipolar plates constitute a large portion of that of fuel cell stacks. Furthermore, more than 80% of the weight of a fuel cell stack comes from the bipolar plates. Although researchers in the field of fuel cells have conducted so much R&D work relevant to the bipolar plate technology, good solutions to this problem is still yet to come. Plastics are not electrically conductive and are poor thermal conductors, but they have the advantages of ease of mass production and low cost. The present thesis proposes a novel design of bipolar plates which can be formed by injection or compression molding process using plastic materials and a current collector can be inset on its surfaces. The current collector together with the gas diffusion layer can conduct electrons easily under certain operating conditions and stack designs. In air-breathing PEMFC's, the low thermal conductivity of plastic materials should pose no problem for heat transfer. The main purpose of the present research is to investigate the feasibility of applying the plastic bipolar plates in the air-breathing PEMFC's.

Because of their high strength to weight ratio, stiffened steel plates are often used in light structures where plates are placed into compression. The stability of steel plates stiffened with longitudinal tee-shaped stiffeners and subjected to uniaxial compression or combined axial compression and out-of-plane bending formed the basis for this research project. The research was conducted to develop a simple approach to assess the post-buckling behaviour of stiffened steel plates and provide a limit states design procedure that accounts for the post-buckling stability in the assessment of the resistance factor. The behaviour of stiffened plates was investigated using a finite element model that had been validated through comparison with test results. An exhaustive parametric study, including 1440 finite element analyses, was conducted to investigate the strength and behaviour of stiffened steel plates. A virtual work model was developed to explain the effect of the formation of a plastic hinge mechanism on the post-buckling strength and behaviour. Combined with the numerical results, the theoretical model confirms that the plastic hinge mechanism can cause a sudden loss of capacity. The required lateral deflection for a plastic hinge development can be calculated using the virtual work model for prediction of the unstable behaviour. Based on a better understanding of the behaviour of stiffened steel plates, a set of design equations were developed to calculate the strength of stiffened steel plate subjected to compression in the direction of the stiffener and out-of-plane bending. The proposed design equations were compared with current design guidelines through a comparison of the design approaches with the finite element analysis results. The proposed method showed much better accuracy than the current design approaches. A reliability analysis was conducted to provide appropriate resistance factors for limit states design. Due to the complexity of the design formulas, the Monte Carlo simulation technique was used to generate the statistical distributions of the predicted strength. The second-moment method was used to calculate the resistance factors for different values of safety index. The resistance factor varied from 0.90 to 0.65 for values of safety index from 2.5 to 4.5, respectively.
Structural Engineering

碩士
逢甲大學
機械與電腦輔助工程學系
103
In this work, the Finite Element software—ANSYS—and Point Stress Criterion are used for the study of fracture strength prediction on plates that are made of thermoplastic woven composite and contain various holes of different radii. First, by the hot-pressed method, carbon fiber woven prepregs soaked through the epoxy impregnation were manufactured into the woven composite plates. Then, by means of metallographic microscope, we observed the cross-section of the woven composite plate along the direction of fiber yarn weaving, and got the ratio of height to length and the fiber volume fraction. Furthermore, Stiffness Averaging method was adopted to calculate the equivalent engineering moduli of the thermoplastic woven composite plates, while the material testing machine was utilized to measure the material’s properties, for verification of the correctness of the estimated value. Next, the engineering moduli and the resulting fracture strengths are input into ANSYS for analysis to obtain the stress distribution beside the hole in this plate. Meanwhile, the characteristic length from the Point Stress Criterion is derived. Finally, the Least-squares method is adopted to set up a functional relationship between characteristic length and hole radius so that the characteristic length of plates whose holes have different radii can be predicted. Then, using the theory of elasticity and the superposition principle, as well as this predicted characteristic length, the predicted fracture strength is calculated. This will be compared with an experimental value. The results indicate that this method works quite accurately to predict the fracture strength of a plate that is made of thermoplastic woven composite, with only a 3% margin of error. Through observation of the woven composite plate after tensile failure using a metallographic microscope, it is found that the multiple fiber breakage can be found at the point of stress concentration around the hole. And there has more delamination has been found on the other side of the specimen.