Littérature scientifique sur le sujet « Thermomechanical finite element »

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior<br>The continuous casting technique in the last four decades has been large used for to production of semi-finished steel. The heat transfer is major mechanism and it occurs in various steps during the continuous casting. The quality of steel is directly related to the way the heat transfer occur because the thermal variations produce mechanical loads as well as contact forces which are generated through the rollers and shake of the mold. Such factors may cause defects such as fractures or cracks in the final product if the resulting stresses and strains exceed critical values. The technique must be improved in order to reduce the appearance of defects and the production time. For this a good understanding of physical phenomena involved during the solidification process is critical. The focus of this work is to apply the EbFVM (Element based Finite-Volume Method) approach to study the effects of linear tensions unidirectionally coupled with the temperature applied to continuous casting of the steel 1013D (0,3% of carbon) In the simulations we adopted some simplifications such as the Plane Strain and isotropic material. We also neglected the body forces contact with the rollers the liquid pressure on the walls of the steel ingot (ferrostatic pressure) and the convective effect. However despite of the simplifications adopted this work provides quantitative informations on the linear tensions accumulation that point out to areas of possible of cracks formations<br>A tÃcnica de lingotamento contÃnuo nas Ãltimas quatro dÃcadas à cada vez mais utilizada na produÃÃo de aÃo semiacabado. A transferÃncia de calor à o principal mecanismo dominante e ocorre em todas as etapas do processo. A qualidade do aÃo no lingotamento està diretamente relacionada à forma que ocorrem as trocas de calor pois as variaÃÃes tÃrmicas produzem carregamentos mecÃnicos assim como as forÃas de contato as quais sÃo geradas por intermÃdio dos rolos e da oscilaÃÃo do molde. Tais fatores podem causar defeitos como fraturas ou trincas no produto final caso as tensÃes e deformaÃÃes resultantes excedam valores crÃticos. O aprimoramento da tÃcnica tem a finalidade de evitar o surgimento de defeitos e reduzir o tempo de produÃÃo. Para isso à fundamental uma boa compreensÃo dos fenÃmenos fÃsicos envolvidos ao longo do processo de solidificaÃÃo. O foco deste trabalho à aplicar a abordagem do EbFVM (Element based Finite-Volume Method) no estudo dos efeitos das tensÃes lineares acopladas unidirecionalmente com a temperatura aplicado ao lingotamento contÃnuo do aÃo 1013D (0,3% de carbono) Nas simulaÃÃes adotou-se algumas simplificaÃÃes com o estado plano de tensÃes e isotropia do material. Descartando-se as forÃas de corpo o contato com os rolos a pressÃo do aÃo lÃquido nas paredes do lingote (pressÃo ferrostÃtica) e o efeito convectivo. Contudo apesar das simplificaÃÃes adotadas este trabalho traz informaÃÃes quantitativas quanto a formaÃÃo do acÃmulo das tensÃes lineares que apontam para regiÃes de possÃveis formaÃÃes de trincas

In this dissertation a finite element procedure using the Disturbed State Concept constitutive models is proposed for the thermomechanical analysis of electronics packaging problems. First, microelectronics packaging types and the problems facing the electronics industry are discussed. Next, the literature in the field of constitutive models and the finite element procedures available for microelectronics packaging materials and interfaces is reviewed. The previous formulation of the Disturbed State Concept is modified so that different stresses and different strains are allowed in the intact and the fully adjusted parts of the material. Furthermore, the thermo elasto-viscoplastic with disturbance constitutive model is improved to handle the continuous temperature change and the hold time. These last features enhance the model so that it can be used in a finite element code to simulate the behavior of the microelectronics packaging materials and interfaces in temperature cycling. A new finite element procedure is developed to implement the improved Disturbed State Concept formulation. The finite element procedure includes a wide range of material models, starting from the linear elastic to thermo elasto-viscoplastic with disturbance. In order to eliminate the finite element mesh sensitivity encountered in strain-softening materials, a new procedure is proposed. The Disturbed State Average Strain method reduces or eliminates the finite element mesh sensitivity. This is proved through a number of example problems. The proposed finite element procedure is verified against a number of sets of experimental data obtained from the literature.

Approved for public release; distribution is unlimited<br>During the consolidation phase, reinforcement particles of Metal Matrix Composites (MMC's) tend to be non uniformly distributed. The result is that the material properties of the composite materials are not as good as those originally desired. Through large amounts of straining, homogeneity can be achieved. Finite element models of MMC's undergoing different thermomechanical processes (TMP's) to true strains of approximately 1.2 were generated. The models consist of particle clusters within the particle-depleted matrix. The particle clusters were modeled by either a smeared model in which the particles refine the grains in the cluster, or a discrete model of the particles within clusters. The smeared and discrete models qualitatively agreed with each other. The results suggest that the best TMP to reach a state of reinforcement particle homogeneity was a hot worked, low strain rate TMP

This research aims at understanding the conditions that lead to reaction initiation of polymer-bonded explosives (PBXs) as they undergo mechanical and thermal processes subsequent to impact. To analyze this issue, a cohesive finite element method (CFEM) based finite deformation framework is developed and used to quantify the thermomechanical response of PBXs at the microstructure level. This framework incorporates the effects of large deformation, thermomechanical coupling, failure in the forms of micro-cracks in both bulk constituents and along grain/matrix interfaces, and frictional heating. A novel criterion for the ignition of heterogeneous energetic materials under impact loading is developed, which is used to quantify the critical impact velocity, critical time to ignition, and critical input work at ignition for non-shock conditions as functions of microstructure of granular HMX and PBX. A threshold relation between impact velocity and critical input energy at ignition for non-shock loading is developed, involving an energy cutoff and permitting the effects of microstructure and loading to be accounted for. Finally, a novel approach for computationally predicting and quantifying the stochasticity of the ignition process in energetic materials is developed, allowing prediction of the critical time to ignition and the critical impact velocity below which no ignition occurs based on basic material properties and microstructure attributes. Results are cast in the form of the Weibull distribution and used to establish microstructure-ignition behavior relations.

This study examines the use of embedded shape memory alloy (SMA)actuators for adaptive control of the themomechanical response of composite structures. Control of static and dynamic responses are demonstrated including thermal buckling, thermal post-buckling, vibration, sonic fatigue, and acoustic transmission. A thermomechanical model is presented for analyzing such shape memory alloy hybrid composite (SMAHC) structures exposed to thermal and mechanical loads. Also presented are (1) fabrication procedures for SMAHC specimens, (2) characterization of the constituent materials for model quantification, (3) development of the test apparatus for conducting static and dynamic experiments on specimens with and without SMA, (4) discussion of the experimental results, and (5) validation of the analytical and numerical tools developed in the study. The constitutive model developed to describe the mechanics of a SMAHC lamina captures the material nonlinearity with temperature of the SMA and matrix material if necessary. It is in a form that is amenable to commercial finite element (FE) code implementation. The model is valid for constrained, restrained, or free recovery configurations with appropriate measurements of fundamental engineering properties. This constitutive model is used along with classical lamination theory and the FE method to formulate the equations of motion for panel-type structures subjected to steady-state thermal and dynamic mechanical loads. Mechanical loads that are considered include acoustic pressure, inertial (base acceleration), and concentrated forces. Four solution types are developed from the governing equations including thermal buckling, thermal post-buckling, dynamic response, and acoustic transmission/radiation. These solution procedures are compared with closed-form and/or other known solutions to benchmark the numerical tools developed in this study. Practical solutions for overcoming fabrication issues and obtaining repeatable specimens are demonstrated. Results from characterization of the SMA constituent are highlighted with regard to their impact on thermomechanical modeling. Results from static and dynamic tests on a SMAHC beam specimen are presented, which demonstrate the enormous control authority of the SMA actuators. Excellent agreement is achieved between the predicted and measured responses including thermal buckling, thermal post-buckling, and dynamic response due to inertial loading. The validated model and thermomechanical analysis tools are used to demonstrate a variety of static and dynamic response behaviors associated with SMAHC structures. Topics of discussion include the fundamental mechanics of SMAHC structures, control of static (thermal buckling and post-buckling) and dynamic responses (vibration, sonic fatigue, and acoustic transmission), and SMAHC design considerations for these applications. The dynamic response performance of a SMAHC panel specimen is compared to conventional response abatement approaches. SMAHCs are shown to have significant advantages for vibration, sonic fatigue, and noise control.<br>Ph. D.

Laser welding is an advanced joining technique with the capability to form deep, narrow, and precise welds. Numerical models are used to simulate the process in attempts of predicting distortions and stresses in the material. This is done to reduce physical testing, optimize processes and enable integrated product- and process development. The Virtual Manufacturing Process research group at University of Skövde wishes to increase their knowledge on modeling options of thermomechanical simulations to grant local industries these benefits. A numerical model for the laser welding process was developed in ABAQUS. This was done by examining the macrograph structure of a simple weld and applied to a stainless-steel T-joint welding application. The macrograph data was used to calibrate a mathematical heat source model. User subroutine DFLUX was used to enable movement of the heat source and element activation was used to simulate the fusion of the two parts. A T-joint welding experiment was carried out to measure deflection and the result was compared to numerical simulations. Different combinations of heat source models, coupling type and element activation was compared in relation to predicting the deflection. Computational time and modeling complexity for the techniques was also considered.The results showed that a 3D Gaussian heat source model will imitate the keyhole weld achieved superior to the compared 2D model. The 3D model provides greater flexibility since it enables combinations of any geometrical bodies. It was shown that element activation has a significant contribution on part stiffness and thus resulting distortions. To implement element activation a fully coupled analysis is required. The deflection of the fully coupled 3D simulation with element activation showed a 9% deviance in deflection compared with experiments.

More efficiency heavy-duty vehicles are developed with higher range, updated electronic and mechanical parts. The fuel efficiency and pollution of carbon dioxide need to be lower to achieve new EU regulations. The global population increases with an increased number of heavy-duty vehicles. This, in turn, increases the emission. By taking the electrical and mechanical parts to the next step, the global emission problems can be massively reduced. Electrical machines are the next step towards a cleaner future. The main goal of this study to investigate the electrical machine’s insulation system. Thermo-mechanical stresses due to thermal cycling affect the electrical machines and its sub-components. By using a FEM application with simplified models of the electrical machine, results are obtained and discussed. Specifically, if 2D-models are sufficient enough to represent a 3D-model. How good different 2D-models can represent the 3D-model is compared and discussed in this study. A physical experimental analysis is done to verify and calibrate the FE-models. Which one of the less frequent higher amplitude or more frequent, lower amplitude thermal cycling affects the insulation system most is determined. The simulations could be done with either, coupled-temperature displacement analysis or sequentially coupled analysis. Coupled-temperature displacement is the fastest method to use in the simulation models. A 3D-model is the best way to describe an object and is therefore implemented. Two additional 2D-models are developed for faster computation and to investigate if the models can represent the three-dimensional geometry. All the models have specific boundary conditions to make the models more simplified. Sensitivity studies have been done to determine which parameter affects the induced thermo-mechanical stresses the most. A physical experimental setup is also implemented to validate and calibrate the simulation model. The result of the 3D-model is most accurate when simulating a three-dimensional object. Simulation results have shown that epoxy, one of the main components in the insulation system, is most critical in terms of reaching breakdown first, followed by paper insulation and copper coating. This is a typical result of all three simulation models. Whereas it is concluded that some 2D-models can present the 3D-model, others can’t. The dependent factor is the different cross-section of the electrical machine. The physical experiment shows similar results between simulation in terms of strain at a lower temperature, and the deviation gets larger as the temperature increases. The 3D-model is the model that has the best representation of a real electrical machine as it accounts for all the normal and shear stress components in all directions, but also because it has better boundary conditions compared to the 2D-models. The 2D-model in XY-plane has shown similar results to the 3D-model. One of the main insulation system components, epoxy, is exposed to the highest stresses compared to its yield and ultimate strength, followed by the paper insulation and copper coating. The sensitivity study has concluded that the axial length of the stator does not affect the stress amplitudes. The most critical parameter that affects the thermo-mechanical stresses is the temperature amplitude, the materials CTE and the thickness of the jointed layer. All maximum stress amplitudes of all the components are located at the free end.<br>Mer effektiva tunga fordon utvecklas med högre räckvidd, uppdaterade elektroniska och mekaniska delar. Bränsleeffektiviteten och föroreningen av koldioxid måste vara lägre för att uppnå nya EU-förordningar. Antalet tunga fordon ökar i takt med att den globala befolkningen ökar, detta leder i sin tur till ökad utsläpp av bland annat koldioxid. Genom att ta de elektriska och mekaniska delarna till nästa steg kan de globala utsläppsproblemen minskas massivt. Elektriska maskiner för framdrivning är nästa steg mot en renare framtid. Studiens huvudmål för att undersöka den elektriska maskinens isoleringssystem. Termomekaniska påfrestningar på grund av termisk cykling påverkar de elektriska maskinerna och dess delkomponenter. Genom att använda en FEM-applikation med förenklade modeller av den elektriska maskinen erhålls och diskuteras resultat. Specifikt om 2D-modeller är tillräckliga för att representera en 3D-modell. Hur tillräckligt de olika 2D-modeller kan representera 3D-modellen jämförs och diskuteras i denna studie. Ett fysiskt experiment utförs för att validera och kalibrera FEA-modellerna. Vilken av de mindre frekventa cykler med högre amplitud eller mer frekventa cyckler med lägre amplitud påverkar isoleringssystemet mest har undersökts. Simuleringarna kan göras med antingen, temperatur kopplad förskjutnings analys eller sekventiellt kopplad analys. Temperatur kopplad kopplad förskjutning är den snabbaste metoden att använda i simuleringsmodellerna. En 3D-modell är det bästa sättet att beskriva ett objekt och har därför implementerats. Ytterligare två, 2Dmodeller är framtagna i FEM-miljö för snabbare beräkning och för att undersöka om 2D-modellerna kan representera den tredimensionella geometrin. Samtliga tre modeller har specifika randvillkor för att förenkla modellerna. Känslighetsstudier görs för att bestämma vilken parameter som påverkar de inducerade termomekaniska spänningarna mest. Ett fysiskt experiment har utförsts för att validera och kalibrera simuleringsmodellerna. Resultatet visar att 3D-modellen representerar ett tre dimensonellt objekt bäst. Simuleringsresultat har visat att epoxy, som är en av huvudkomponenterna i isoleringssystemet, är mest kritisk när det gäller att först nå brott- och sträckgräns, följt av pappersisolering och koppar beläggningen. Detta är ett typiskt resultat av alla tre simuleringsmodeller. Slutsatsen visar att vissa 2D-modeller kan presentera 3D-modellen, andra kan inte. Den beroende faktorn beror på ur vilket tvärsnitt man tittar på den elektriska maskinen. Det fysiska experimentet visar liknande resultat jämfört med simuleringen när det gäller belastning vid en lägre temperatur, och avvikelsen blir större när temperaturen ökar. 3D-modellen, är den modell som har den bästa representationen av en riktig elektrisk maskin eftersom den inkluderar normal- och skjuvspänningskomponenter i alla riktningar. Anledningen är att den har bättre randvillkor jämfört med 2Dmodellerna. 2D-modellen i XY-planet har visat liknande resultat som 3D-modellen. En av huvudkomponenterna i isoleringssystemet, epoxy, utsätts för de högsta spänningarna jämfört med dess sträck- och den brottgräns, följt av pappersisolering och koppar beläggning. Känslighetsstudien har kommit fram till att statorns axiella längd inte påverkar spänningsamplituderna. Den mest kritiska parametern som påverkar de termomekaniska spänningarna är temperatur amplituden, materialens CTE och tjockleken på det skarvade skiktet. Alla maximala spänningsamplituder för samtliga tre komponenter är belägna i den fria änden.