Brazing, as a type of joining process, is widely used in manufacturing industries to join individual components of a structure. Structural reliability of a brazed assembly is strongly dependent on the joint mechanical properties. In the present work, mechanical reliability of low carbon steel brazed joints with copper filler metal is investigated and a methodology for failure analysis of brazed joints using the cohesive zone model (CZM) is presented. Mechanical reliability of the brazed joints is characterized by strength and toughness. Uniaxial and biaxial strengths of the joints are evaluated experimentally and estimated by finite element method using the ABAQUS software. Microstructural analysis of the joint fracture surfaces reveals different failure mechanisms of dimple rupture and dendritic failure. Resistance of the brazed joints against crack propagation, evaluated by the single-parameter fracture toughness criterion, shows dependency on the specimen geometry and loading configuration. Fracture of the brazed joints and the subsequent ductile tearing process are investigated using a two-parameter CZM. The characterizing model parameters of the cohesive strength and cohesive energy are identified by a four-point bend fracture test accompanied with corresponding FE simulation. Using the characterized CZM, the joint fracture behavior under tensile loading is well estimated. Predictability of the developed cohesive zone FE model for fracture analysis of brazed joints independent of geometry and loading configuration is validated. The developed cohesive zone FE model is extended to fatigue crack growth analysis in brazed joints. A cyclic damage evolution law is implemented into the cohesive zone constitutive model to irreversibly account for the joint stiffness degradation over the number of cycles. Fatigue failure behavior of the brazed joints is characterized by performing fully reversed strain controlled cyclic tests. The damage law parameters are calibrated based on the analytical solutions and the experimental fatigue crack growth data. The characterized irreversible CZM shows applicability to fatigue crack growth life prediction of brazed joints.

Finite element analysis using Cohesive Zone Method (CZM) is a commonly used method to investigate delamination in laminated composites. In this study, two plane strain, zero-thickness six-node quadratic (6-NQ) and four-node linear (4-NL) interface elements are developed to implement CZM. Two main approaches for CZM formulation are categorized as Unified Mode Approach (UMA) and Separated Mode Approach (SMA), and implemented into 6-NQ interface elements to model a double cantilever beam (DCB) test of a unidirectional laminated composite. The results of the approaches are nearly identical. However, it is theoretically shown that SMA spawns non-symmetric tangent stiffness matrices, which may lower convergence and/or overall performance, for mixed-mode loading cases. Next, a UMA constitutive relationship is rederived. The artificial modifications for improving convergence rates such as lowering penalty stiffness, weakening interfacial strength and using 6-NQ instead of 4-NL interface elements are investigated by using the derived UMA and the DCB test model. The modifications in interfacial strength and penalty stiffness indicate that the convergence may be improved by lowering either parameter. However, over-softening is found to occur if lowering is performed excessively. The morphological differences between the meshes of the models using 6-NQ and 4-NL interface elements are shown. As a consequence, it is highlighted that the impact to convergence performance and overall performance might be in opposite. Additionally, benefits of selecting CZM over other methods are discussed, in particular by theoretical comparisons with the popular Virtual Crack Closure Technique. Finally, the numerical solution scheme and the Arc-Length Method are discussed.

<p>In this thesis an experimental method to calculate cohesive characteristics for an adhesive layer in a End Notched Flexure (ENF) specimen is presented and evaluated. The method is based on the path independent J-integral where the energy release rate (ERR) for the adhesive is derived as a function of the applied forces and the rotational displacements at the loading point and at the supports of the specimen. The major advantage with the method in comparison with existing theory known by the job initiator is that it is still applicable with ENF specimens that are subjected to yielding of the adherends.</p><p>The structure of this thesis is disposed so that the theory behind the J-integral method is shortly described and then an evaluation of the method is performed by aid of finite element simulations using beam and cohesive elements. The finite element simulations indicates that the ERR can be determined with good accuracy for an ENF specimen where a small scale yielding of the adherends has occurred. However when a fully cross sectional yielding of the adherends is reached the ERR starts diverging from the exact value and generates a too high ERR according to input data in the simulations, i.e. the exact values. The importance in length of the adhesive process zone is also shown to be irrelevant to the ERR measured according to the J-integral method.</p><p>Simulation performed with continuum elements indicates that a more reality based FE- simulation implies a higher value of the applied load in order to create crack propagation. This is an effect of that the specimen is allowed to roll on the supports which makes the effective length between the supports shorter than the initial value when the specimen is deformed. This results in a stiffer specimen and thus a higher applied force is needed to create crack propagation in the adhesive layer.</p><p>An experimental set up of an ENF specimen is created and the sample data from the experiments are evaluated with the J-integral method. For measuring the rotational displacements of the specimen which are needed for the J-integral equation an image system is developed by the author and validated by use of linear elastic beam theory. The system calculates the three rotational displacements of the specimen by aid of images taken by a high resolution SLR camera and the system for measuring the rotations may also be used in other applications than for a specific ENF geometry. The validation of the image system shows that the rotations calculated by the image system diverge from beam theory with less than 2.2 % which is a quite good accuracy in comparison with the accuracies for the rest of the used surveying equipment.</p><p>The results from the experiment indicates that the used, about 0.36 mm thick SikaPower 498, adhesive has an maximum shear strength of 37.3 MPa and a critical shear deformation of 482 µm. The fracture energy is for this thickness of the adhesive is determined as 12.9 kJ/m².</p><p>This report ends with a conclusion- and a suggested future work- chapter.</p>

No description available.

Over the last few decades, Shape Memory Alloys (SMAs) have been increasingly explored in order to take advantage of their unique properties (i.e., pseudoelasticity and shape memory effect), in various actuation, sensing and absorption applications. In order to achieve an effective design of SMA-based devices a thorough investigation of their behavior in the presence of cracks is needed. In particular, it is important to understand the effect of phase transformation on their fracture response. The aim of the present work is to study the effect of stress-induced as well as thermo-mechanically-induced phase transformation on several characteristics of the fracture response of SMAs. The SMA thermomechanical response is modeled through an existing constitutive phenomenological model, developed within the framework of continuum thermodynamics, which has been implemented in a finite element frame-work. The effect of stress-induced phase transformation on the mechanical fields in the vicinity of a stationary crack and on the toughness enhancement associated with crack advance in an SMA subjected to in-plane mode I loading conditions is examined. The small scale transformation assumption is employed in the analysis according to which the size of the region occupied by the transformed material forming close to the crack tip is small compared to any characteristic length of the problem (i.e. the size of the transformation zone is thirty times smaller than the size of the cracked ligament). Given this assumption, displacement boundary conditions, corresponding to the Irwin’s solution for linear elastic fracture mechanics, are applied on a circular region in the austenitic phase that encloses the stress-induced phase transformation zone. The quasi-static stable crack growth is studied by assuming that the crackpropagates at a certain critical level of the crack-tip energy release rate. The Virtual Crack Closure Technique (VCCT) is employed to calculate the energy release rate. Fracture toughness enhancement associated with transformation dissipation is observed and its sensitivity on the variation of key characteristic non-dimensional parameters related to the constitutive response is investigated. Moreover, the effect of the dissipation due plastic deformation on the fracture resistance is analyzed by using a Cohesive Zone Model (CZM). The effect of thermo-mechanically-induced transformation on the driving force for crack growth is analyzed in an infinite center-cracked SMA plate subjected to thermal actuation under isobaric mode I loading. The crack-tip energy release rate is identified as the driving force for crack growth and is measured over the entire thermal cycle by means of the VCCT. A substantial increase of the crack-tip energy release rate – an order of magnitude for some material systems – is observed during actuation as a result of phase transformation, i.e., martensitic transformation occurring during actuation causes anti-shielding that might cause the energy release rate to reach the critical value for crack growth. A strong dependence of the crack-tip energy release rate on the variation of the thermomechanical parameters characterizing the material response is examined. Therefore, it is implied that the actual shape of the strain- temperature curve is important for the quantitative determination of the change of the crack-tip energy release rate during actuation.

No description available.

The aim of this paper was to analyze the impact of the genre on the use of cohesive devices in the literary and legal texts. To achieve the aim the following objectives were specified: to determine the typical patterns of the use of cohesive devices in literary and legal texts and to identify similarities and differences of the use of cohesive devices in the texts of different genres under investigation. The approaches to the research were quantitative and qualitative as well as content analysis method was chosen for the analysis. The research demonstrated that the genre has an evident influence on the density and distribution of cohesive devices. It also demonstrated that most often used cohesive devices in fiction belong to the group of reference and in legal documents to the group of lexical cohesion. The amassed data showed that the literary genre demonstrates all possible types of substitution and ellipsis whereas in the legal genre this type of cohesive devices has very low frequency. In addition, conjunction was identified as the least commonly employed type of cohesive devices in fiction as well as in the legal documents. Cohesive devices are important in all types of communication as they signal to the addressee the connections between the sentences of the text; therefore, the further studies are required to determine the influence of textual genre on the choice of cohesive devices in the genres that were not thoroughly investigated before. / Tyrimo tikslas yra panagrinėti, kokią įtaką teksto žanras turi renkantis tarpfrazinio ryšio priemones literatūriniame ir teisiniame žanruose. Suformuluoti šie tyrimo uždaviniai: apibrėžti tipiškus tarpfrazinio ryšio priemonių vartojimo literatūriniame ir teisiniame tekstuose modelius ir identifikuoti tarpfrazinio ryšio priemonių vartojimo panašumus ir skirtumus tirtuose skirtinguose žanruose. Tarpfrazinio ryšio priemonių vartojimo dažnumui ištirti buvo taikytas kiekybinis požiūris. Žanro įtaka tarpfrazinio ryšio priemonių pasirinkimui buvo vertinta kokybiniu požiūriu. Tarpfrazinio ryšio priemonėms tekstuose išskirti buvo panaudotas turinio analizės metodas. Tyrimas parodė, kad teksto žanras iš esmės nulemia tarpfrazinio ryšio priemonių vartojimo dažnumą ir jų pasiskirstymą tekste. Dažniausiai vartojamos tarpfrazinio ryšio priemonės literatūriniame tekste priklauso referencijos tipui, o teisiniuose dokumentuose – leksinio tarpfrazinio ryšio priemonių tipui. Literatūrinio žanro tekste sutinkami visi substitucijos ir elipsės tipai, tuo tarpu kai teisinio žanro tekste šis tarpfrazinio ryšio tipas yra vienas iš rečiausiai vartojamų. Jungtukinis ryšys ir literatūrinio, ir teisinio žanrų tekstuose yra rečiausias. Tarpfrazinio ryšio priemonės yra svarbios visoms komunikacijos formoms, nes jos signalizuoja adresatui jungtis tarp sakinių. Siekiant apibrėžti teksto žanro įtaką tarpfrazinio ryšio priemonių pasirinkimui žanruose, kurie iki šiol nėra pakankamai ištirti, yra reikalingos... [toliau žr. visą tekstą]

Dans un contexte de réduction de la masse des aéronefs pour une diminution de la consommation de carburant, l'assemblage par collage représente une alternative intéressante aux assemblages boulonnés. Toutefois, les avantages des assemblages collés ne sont pas pleinement exploités, notamment de par le manque de confiance accordée dans les méthodes de dimensionnement leur étant associés. C'est pourquoi, l'objectif de ce travail était de proposer une démarche de modélisation pour la prévision de l'amorçage d'une fissure dans ce type d'assemblages sous des sollicitations statiques. De nombreux paramètres influents jouent sur la tenue à l'amorçage dans un assemblage collé. En particulier, cette tenue est fortement dépendante de l'épaisseur de la colle de cet assemblage. Aussi, dans un premier temps, l'influence de ce paramètre a été évaluée par une approche par critère couplé pour lequel une nouvelle définition de la mixité de mode a été proposée afin de traduire la dépendance de la résistance et de la ténacité du joint au mode de chargement. La mise en oeuvre du critère couplé a permis de retrouver l'influence, observée expérimentalement, de l'épaisseur de colle sur la tenue lors d'un essai à simple recouvrement, à savoir que plus l'épaisseur de colle est fine, meilleure est la tenue. Dans un deuxième temps, il s'est agit de mettre à profit la compréhension acquise précédemment en prenant en compte de l'épaisseur de colle dans un modèle de zone cohésive composé des mêmes ingrédients que le critère couplé mais qui est applicable dans le cas de structures en 3D. Le modèle de zone cohésive ainsi proposé rend compte de l'influence de l'épaisseur de colle sur l'amorçage identifiée par le critère couplé. Finalement, les apports et les limites de la démarche de modélisation proposée ont été mis en évidence à l'aide de comparaisons avec des résultats expérimentaux issus de la littérature.

Brazing, as a type of joining process, is widely used in manufacturing industries to join individual components of a structure. Structural reliability of a brazed assembly is strongly dependent on the joint mechanical properties. In the present work, mechanical reliability of low carbon steel brazed joints with copper filler metal is investigated and a methodology for failure analysis of brazed joints using the cohesive zone model (CZM) is presented. Mechanical reliability of the brazed joints is characterized by strength and toughness. Uniaxial and biaxial strengths of the joints are evaluated experimentally and estimated by finite element method using the ABAQUS software. Microstructural analysis of the joint fracture surfaces reveals different failure mechanisms of dimple rupture and dendritic failure. Resistance of the brazed joints against crack propagation, evaluated by the single-parameter fracture toughness criterion, shows dependency on the specimen geometry and loading configuration. Fracture of the brazed joints and the subsequent ductile tearing process are investigated using a two-parameter CZM. The characterizing model parameters of the cohesive strength and cohesive energy are identified by a four-point bend fracture test accompanied with corresponding FE simulation. Using the characterized CZM, the joint fracture behavior under tensile loading is well estimated. Predictability of the developed cohesive zone FE model for fracture analysis of brazed joints independent of geometry and loading configuration is validated. The developed cohesive zone FE model is extended to fatigue crack growth analysis in brazed joints. A cyclic damage evolution law is implemented into the cohesive zone constitutive model to irreversibly account for the joint stiffness degradation over the number of cycles. Fatigue failure behavior of the brazed joints is characterized by performing fully reversed strain controlled cyclic tests. The damage law parameters are calibrated based on the analytical solutions and the experimental fatigue crack growth data. The characterized irreversible CZM shows applicability to fatigue crack growth life prediction of brazed joints.

Orientador: Bernardo Mançano Fernandes / Banca: Eliseu Savério Sposito / Banca: Everaldo Santos Melazzo / Banca: Elpídio Serra / Banca: Rubens Galdino da Silva / Abstract: Development, despite the completion the term incites, occurs unequally in the midst of different areas and regions. According to the monopolistic logic that bases the social and economical process, society understakes the environment wich we are daily exposed to Nova Alta Paulista, located in the farwest of the state of São Paulo, was developed in the mid of the twentieth century, together with the urban industrialization on course in the metropolitan area in state control. External factors, such as the international conjuncture, besides the governmentþs move inspired by the national development trend, combined with internal factors, such as certain characteristics of the environment, local policies, and the predominance of a resistant conception to the consolidation of regional debates, contributed to a minor socioeconomical situation in the context of the state. Current affairs are leading us to important changes on environmental and territorial organization under the tendency to renewable sources of energy. Such fact demands reflection and study on its impact over development in the region. In this study, the objectives were to analyse how the socioeconomical development of Nova Alta Paulista took place to understand its current face; to examine the adjustment to the idea of a suppressed region to designate its socioeconomical and political cultural characteristics; to make use of a new approach that suprpasses the conception of territory, conceiving it as a social development which results from the conception of region to a territorial notion; to verify If the idea of regional development, named endogeneous development, will be able to territorialize, beginning with the socioeconomical actions under taken by local parties and segments in conflict with current hegemonical powers... (Complete abstract, click electronic address below) / Doutor