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Lindberg, Filip. "Sheet Metal Forming Simulations with FEM". Thesis, Umeå universitet, Institutionen för fysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-51527.
Testo completoAbstract (sommario):
The design of new forming tools get more problemtic as the geometries get more complicated and the materials less formable. The idea with this project is to evaluate if an implementation of a simulation software in the designing process, to simulate the forming process before actually building the tools, could help Duroc Tooling avoid expensive mistakes. To evaluate this, the commercial FEM simulation software LS-DYNA was used in a complicated project, where the design of the forming tools for forming a girder was considered. The main objective was to avoid cracking and severe wrinkling which may result in the forming process. With help of simulations a stable forming process which did not yield cracks or severe wrinkling, was eventually found. The girder was almost impossible to form without cracking, but the breakthrough came when we tried to simulate a preforming step which solved the problem. Without a simulation software this would never have been tested since it would be to risky and expensive to try an idea which could turn out to be of no use. The simulations also showed that the springback - shape deformation occuring after pressing - was large and hard to predict without simulations. Therefore, the tools were also finally springback compensated. We concluded that simulations are very effective to quickly test new ideas which may be necessary when designing the tools for forming complicated parts. Simulation also provided detailed quantitative information about the expected cracks, wrinkles, and weaknesses of the resulting pieces. Even though there is cost associated with simulations, it is obvious from this project that a simulation software is a must if Duroc Tooling wants to be a leading company in sheet metal forming tools, and stand ready for the higher demands on the products in the future.
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Adams, Donat Jozsef. "Ab initio simulations of Earth forming minerals /". kostenfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:30017.
Testo completo
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Thije, René Hermanus Willem ten. "Finite element simulations of laminated composite forming processes". Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/57908.
Testo completo
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Bentsrud, Herman. "Friction and material modelling in Sheet Metal Forming Simulations". Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-19686.
Testo completoAbstract (sommario):
In today’s car manufacturing industry, sheet metal forming is a important process that takes preparation, which is time consuming and complex when new processes are made. When new metal grades and alloys are provided to the industry, tests are conducted to determine it’s behaviour and strengths. This gives the data for complex material models that can approximate the metal behaviour in an accurate way in a simulation environment. One of the unknown factors from tests is the friction coefficient on the sheet metal. The software Triboform is able to provide an adaptable friction coefficient model that depends on multiple simulation and user input conditions. The problems that occur when acquiring data for the material model is that testing is time consuming and the friction model has to be adjusted to give accurate results. At Volvo Cars there are two material models used with their different advantages, BBC 2005 and Vegter 2017.The purpose with this work is to compare the two material models using the Triboform friction models implemented to see if any combination provides accurate simulation results and then create recommendations for which model is best suited for different cases. Some side studies is also done with an older Vegter model, a strain rate sensitive BBC 2005 model and a Triboform model on all simulation parts.The purpose is achieved by implementing the Triboform model in Autoform and run a simulation of a Limiting Dome Height (LDH) test with both material models and compare the results with experimental data for several different materials. The data that is directly compared from the LDH test is the major and minor strain from two perpendicular sections at four different stages and also the force from the punch tool. The material models will be evaluated by how it manages to mimic the strain behaviour of the metals and how it estimates the punch force.The results point towards an improvement of the accuracy for most of the metals tested and BBC 2005 is the better model if there’s available biaxial data from tests, Vegter 2017 is decent if there’s not. However Vegter 2017 is not a good option for aluminum alloys simulations when the punch force is compared. Side study also shows that Vegter 2017 is bit of a downgrade when it comes to strain values, compared to the old Vegter.The work, in summary shows a dynamic friction model can improve the accuracy for strain predictions in the simulation process. If there’s biaxial yield data available for the metal or if it’s an aluminum alloy, BBC 2005 is the superior choice, but if only tensile tests are available for metals, Vegter 2017 is a decent choice for some cases.I dagens bilindustri är plåtmetalformning en viktig process som kräver förberedelser som är tidskonsumerande och komplex när nya processer tillkommer. När nya metallslag kommer in till industrin, så utförs tester för att avgöra dess egenskaper och styrka. Denna testdata används till materialmodeller som kan approximera metallens beteende på ett noggrant sätt i en simuleringsmiljö. Den okända faktorn från dessa test är friktionskoefficienten på plåten. Programvaran Triboform är kapabel att göra en dynamisk friktionsmodel som beror på användar- och simuleringsdata. Problemen som uppstår vid framtagning av data är att det är tidskonsumerande och flera simuleringar måste göras för att bestämma friktionen. Volvo Cars använder sig av två modeller med olika fördelar, BBC 2005 och Vegter 2017.Syftet med detta arbete är att jämföra de två materialmodellerna med Triboform modeller implementerat för att se om de påverkar noggrannheten i simuleringar och sedan förse rekommendationer för vilken modell passar bäst för olika fall. Några sidojobb i studien som görs är en jämförelse med gamla Vegter modellen, ett test med en modell som är känslig för töjningshastighet och test med att implementera Triboform modellen på alla pressverktyg.Detta utförs med att implementera Triboform modellerna i Autoform och köra en simulering på ett LDH-test med båda materialmodeller och jämföra resultaten med experimentell data för flera olika metaller. Data som skall jämföras från LDH-testet är första och andra huvudtöjningen i två vinkelräta sektioner i fyra processsteg och stämpelkraften genom hela processen. Modellerna kommer evalueras genom hur de lyckas imitera töjningens beteende och hur den estimerar stämpelkraften.Resultaten pekar mot en förbättring när Triboform är implementerat i simuleringar för de flesta metaller som ingår i testen och BBC 2005 är den model som föredras om det finns tillgänglig biaxiel spänning data från tester, Vegter 2017 är en duglig modell om dessa data inte finns. Vegter 2017 är dock inte ett bra alternativ när det kommer till jämförelse av töjning och stämpelkraften för aluminium. Sidojobb med gamla Vegter visar att den nya Vegter 2017 inte är en direkt förbättring med hänsyn till noggrannheter av krafter och töjningar.Arbetet visar att en dynamisk friktionsmodel kan förbättra prediktering av töjningar i simuleringar. Om det finns biaxiel data för metallen eller om det gäller att simulera aluminium är BBC 2005 det bättre altermativet, om det endast finns dragprovsdata för metallen så är Vegter 2017 duglig för vissa fall.
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Pilthammar, Johan. "Elastic Press and Die Deformations in Sheet Metal Forming Simulations". Licentiate thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-15481.
Testo completoAbstract (sommario):
Never before has the car industry been as challenging, interesting, and demanding as it is today. New and advanced techniques are being continuously introduced, which has led to increasing competition in an almost ever-expanding car market. As the pace and complexity heightens in the car market, manufacturing processes must advance at an equal speed. An important manufacturing process within the automotive industry, and the focus of this thesis, is sheet metal forming (SMF). Sheet metal forming is used to create door panels, structural beams, and trunk lids, among other parts, by forming sheets of metal in press lines with stamping dies. The SMF process has been simulated for the past couple of decades with finite element (FE) simulations, whereby one can predict factors such as shape, strains, thickness, springback, risk of failure, and wrinkles. A factor that most SMF simulations do not currently include is the die and press elasticity. This factor is handled manually during the die tryout phase, which is often long and expensive. The importance of accurately representing press and die elasticity in SMF simulations is the focus of this research project. The research objective is to achieve virtual tryout and improved production support through SMF simulations that consider elastic die and press deformations. Loading a die with production forces and including the deformations in SMF simulations achieves a reliable result. It is impossible to achieve accurate simulation results without including the die deformations. This thesis also describes numerical methods for optimizing and compensating tool surfaces against press and die deformations. In order for these compensations to be valid, it is imperative to accurately represent dies and presses. A method of measuring and inverse modeling the elasticity of a press table has been developed and is based on digital image correlation (DIC) measurements and structural optimization with FE software. Optimization, structural analysis, and SMF simulations together with experimental measurements have immense potential to improve simulation results and significantly reduce the lead time of stamping dies. Last but not least, improved production support and die design are other areas that can benefit from these tools.Aldrig tidigare har bilindustrin varit så utmanande, intressant och spännande som idag. Ny och avancerad teknik introduceras i en allt snabbare takt vilket leder till ständigt ökande konkurrens på en, nästan ständigt, ökande bilmarknad. Den ständigt ökande komplexiteten ställer även krav på tillverkningsprocesserna. En viktig process, som denna licentiatuppsats fokuserar på, är pressning av plåt. Tillverkningstekniken används för att forma plåtar till dörrpaneler, strukturbalkar, motorhuvar, etc. Plåtar formas med hjälp av pressverktyg monterade i plåtformningspressar. Plåtformningsprocessen simuleras sedan ett par decennium tillbaka med Finita Element (FE) simuleringar. Man kan på så sätt prediktera form, töjningar, tjocklek, återfjädring, rynkor, risk för försträckning och sprickor m.m. En faktor som för tillfället inte inkluderas i näst intill alla plåtformningssimuleringar är elastiska press- och verktygsdeformationer. Detta hanteras istället manuellt under, den oftast långa och dyra, inprovningsfasen. Detta projekt har visat på vikten av att representera press och verktygsdeformationer i plåtformningssimuleringar. Detta demonstreras genom en analys av ett verkligt pressverktyg som belastas med produktionskrafter. Det är inte möjligt att uppnå bra simuleringsresultat utan att inkludera verktygsdeformationer i simuleringsmodellen. Uppsatsen beskriver även numeriska metoder för att optimera och kompensera verktygsytor mot press och verktygsdeformationer. För att dessa kompenseringar ska stämma är det viktigt att man representerar både verktyg och press på ett korrekt sätt. Förslag på en metod för att mäta och inversmodellera pressdeformationer har utvecklats, metoden är baserad på mätningar med DIC-systemet ARAMIS och optimering i FE-mjukvaror. Optimering, strukturanalys, och plåtformningsanalys tillsammans med experimentella mätningar har en stor potential att förbättra plåtformningssimuleringar samt reducera ledtiden för pressverktyg. Sist men inte minst, andra positiva effekter är en enklare och smidigare konstruktionsprocess och förbättrad produktionssupport.
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Allesson, Sara. "Sheet Metal Forming Simulations with Elastic Dies: Emphasis on Computational Cost". Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-18236.
Testo completoAbstract (sommario):
The car industry produces many of their car parts by using sheet metal forming, where one of the most time-consuming phases is the development and manufacturing of new forming tools. As of today, when a new tool is to be evaluated in terms of usability, a forming simulation is conducted to predict possible failures before manufacturing. The assumption is then that the tools are rigid, and the only deformable part is the sheet metal itself. This is however not the case, since the tools also deform during the forming process. A previous research, which is the basis of this thesis, included a model with only elastic tools and showed results of high accuracy in comparison to using a rigid setup. However, this simulation is not optimal to implement for a daily based usage, since it requires high computational power and has a long simulation time. The aim and scope for this thesis is to evaluate how a sheet metal forming simulation with elastic tool consideration can be reduced in terms of computational cost, by using the software LS-DYNA. A small deviation of the forming result is acceptable and the aim is to run the simulation with a 50-75 % reduction of time on fewer cores than the approximate 14 hours and 800 CPUs that the simulation requires today. The first step was to alter the geometry of the tools and evaluate the impact on the deformations of the blank. The elastic solid parts that only has small deformations are deleted and replaced by rigid surfaces, making the model partly elastic. Later, different decomposition methods are studied to determine what kind that makes the simulation run faster. At last, a scaling analysis is conducted to determine the range of computational power that is to be used to run the simulations as efficient as possible, and what part of the simulation that is affecting the simulation time the most. The correlation of major strain deviation between a fully elastic model and a partly elastic model showed results of high accuracy, as well as comparison with production measurements of a formed blank. The computational time is reduced by over 90 % when using approximately 65 % of the initial computational power. If the simulations are run with even less number of cores, 10 % of the initial number of CPUs, the simulation time is reduced by over 70 %. The conclusion of this work is that it is possible to run a partly elastic sheet metal forming simulation much more efficient than using a fully elastic model, without reliability problems of the forming results. This by reducing the number of elements, evaluate the decomposition method and by conducting a scaling analysis to evaluate the efficiency of computational power.Bilindustrin producerar många av sina bildelar genom att tillämpa plåtformning, där en av de mest tidskrävande faserna är utveckling och tillverkning av nya formningsverktyg. Idag, när ett nytt verktyg ska utvärderas med avseende på användbarhet, genomförs en formningssimulering för att förutsäga eventuella fel innan tillverkning. Antagandet är då att verktygen är stela och den enda deformerbara delen är själva plåten. Det är dock inte så, eftersom verktygen också deformeras under formningsprocessen. Tidigare forskning, som ligger till grund för detta examensarbete, inkluderade en modell med endast elastiska verktyg och visade resultat med hög noggrannhet i jämförelse med att använda stela verktyg. Simuleringen med elastiska verktyg är emellertid inte optimal att implementera för daglig användning, eftersom den kräver hög beräkningskraft och har en lång simuleringstid. Syftet och omfattningen av detta examensarbete är att utvärdera hur en plåtformningssimulering med elastiska verktyg kan minskas med avseende på beräkningskostnaden, genom att använda programvaran LS-DYNA. En liten avvikelse från formningsresultatet är acceptabelt, och målet är att köra simuleringen med en 50-75 % minskning av tiden på färre kärnor än ungefär 14 timmar och 800 processorer som simuleringen kräver idag. Det första steget är att ändra verktygets geometri och utvärdera inverkan på deformationerna av plåten. De elastiska solida verktygsdelarna som endast har små deformationer raderas och ersätts av stela ytor, vilket gör modellen delvis elastisk. Senare studeras olika dekompositionsmetoder för att avgöra vilka som gör simuleringen snabbare. Till sist utförs en skalningsanalys för att bestämma antalet processorer som ska användas för att köra simuleringen så effektivt som möjligt. Korrelationen av huvudtöjningarna mellan en helt elastisk modell och en delvis elastisk modell visade resultat av hög noggrannhet, såväl som jämförelse med produktionsmätningar av en format plåt. Beräkningstiden minskar med över 90 % när man använder ungefär 65 % av den ursprungliga beräkningskraften. Om simuleringarna körs med färre antal kärnor, cirka 10 % av ursprungligt antal CPUer, minskar simuleringstiden med 70 %. Slutsatsen av detta arbete är att det är möjligt att köra en delvis elastisk plåtformningssimulering mycket effektivare än att använda en helt elastisk modell, utan att de resulterar i pålitlighetsproblem. Detta genom att minska antalet element, utvärdera dekompositionsmetoden och genom att genomföra en skalningsanalys för att utvärdera effektiviteten av beräkningskraften.
Reduced Lead Time through Advanced Die Structure Analysis - Swedish innovation agency Vinnova
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Kulasegaram, S. "Development of particle based meshless method with applications in metal forming simulations". Thesis, Swansea University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637828.
Testo completoAbstract (sommario):
Finite element formulations dealing with geometric and material non-linearities have been well developed and a significant amount of work has been accomplished for the numerical simulation of metal forming processes. Nevertheless, standard finite element approaches can be sometimes ineffective in handling bulk material deformation owing to severe mesh distortion or mesh entanglement. In the past, some finite element methods such as the Arbitrary Lagrangian Eulerian (ALE) method have been introduced to allow continuous remeshing during computation. Though rather effective in handling large deformation and keeping track of moving boundaries, these methods required extensive computational effort. In this thesis an attempt is made to address the aforementioned problems by using particle based Lagrangian techniques in the numerical simulation of large deformation metal forming processes. For this purpose a particle method called Corrected Smooth Particle Hydrodynamics (CSPH) is considered in the present work. CSPH method is developed from Smooth Particle Hydrodynamics (SPH) techniques which originated twenty years ago. Like most of the particle methods the CSPH also requires no explicit mesh for the computation and therefore avoids mesh direction difficulties in large deformation analysis. In addition, CSPH can achieve similar order of accuracy as any other modern mesh-less methods while retaining the simplicity of the original SPH technique. The simplicity and robustness of SPH method are demonstrated in the first few chapters of this thesis. As a first step of the present research, the SPH method is studied for evaluating its consistency, accuracy and other characteristics. As a consequence of these analyses various correction procedures are introduced in the original SPH method to enhance its performance. The resulting method is referred to here as the Corrected SPH technique. The CSPH is then used to formulate the viscoplastic forming problems with the aid of flow formulation technique.
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Gittins, D. "Hydrodynamical simulations of interstellar gas : from star-forming clouds to spiral arms". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.599430.
Testo completoAbstract (sommario):
This thesis presents numerical investigations of interstellar gas under various conditions. Discrete, pressure-bounded gas ‘cloudlets’ are modelled with Smoothed Particle Hydrodynamics (SPH) which is shown to reproduce accurately their properties and the outcomes of collisions between them. A simple model of a molecular cloud is investigated, consisting of a spherical ensemble of such cloudlets. This model dissipates its kinetic energy on a timescale controlled by the collision timescale. Distributed star formation does not result, and hierarchical mergers of cloudlets do not play a significant part, due to the high Mach number of collisions. A model gravitational potential for a spiral galaxy is introduced, and the interaction of large groups of cloudlets with this potential is investigated. Density and velocity structure are induced by the passage through a spiral arm. Comparisons to observed molecular clouds fail to reproduce the correct size-linewidth relation. The response of a uniform gaseous galactic disc to the spiral potential is investigated using two-dimensional SPH, a two-dimensional Eulerian code and a semi-analytical approach. Good agreement in the predicted location of spiral shocks is seen between all methods. Instability of spiral arms in open spirals is found, and possible formation mechanism of spur-like structure are discussed. The location of spiral shocks relative to the peaks of the stellar surface density is proposed as a new way to constrain the corotation radius in spiral galaxies. The potential form an N-body simulation of a galaxy is introduced and the response of the gaseous disc shows complex and rapidly changing structure. Observational implications for spatial galaxies are suggested.
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Hambrecht, Jochen Dieter. "Elastic-plastic return algorithms for sheet metal forming simulations and springback analysis /". The Ohio State University, 1993. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487847761309225.
Testo completo
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Abrass, Ahmad [Verfasser]. "Simulations of Roll Forming Processes on the Basis of Steady State Properties / Ahmad Abrass". Aachen : Shaker, 2014. http://d-nb.info/1058315773/34.
Testo completo
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Mohamad, Jasri Bin. "Springback prediction in sheet metal forming : constitutive equations, finite element simulations and experimental validation". Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=22712.
Testo completoAbstract (sommario):
Predictive methods appear to be the most effective way to solve springback in sheet metal forming. The accuracy of the predictions depends upon the application of accurate material modelling. Experimental devices and methods are being continuously improved to incorporate increasingly accurate plastic bending characteristics. As part of these efforts, a new tool has been developed to test and record the characteristics of sheet metal deformation by investigating the Bauschinger effect factors (BEF) and the identified hardening parameters. The developed tool is believed to simulate the actual forming conditions of bending and provide more reliable information. The initial experimental investigation shows that the Bauschinger effect does occur during bending and unbending loadings in sheet metal forming. The BEF value was found to increase as the thickness increases. Therefore this justifies the need to consider the Bauschinger effect in sheet metal forming simulation through the use of relevant constitutive equations. A direct optimization method has been successfully applied to identify material hardening parameters from the acquired experimental data of the newly developed tool. The optimisation result shows that nonlinear kinematic hardening and nonlinear mixed hardening models are capable of fitting the smooth transition curve of the experimental hardening data. Mixed hardening model performance however is considered to be much better as proven by lower residual or fitting error values. This justifies the idea that the application of a mixed hardening model is more suitable for springback simulation in sheet metal forming. Validation work was conducted in order to test the effectiveness of applying the two hardening models by incorporating the identified parameters in predicting springback using finite element simulation. Of the two, the mixed hardening modelling has been proven to provide better simulation results in predicting springback.
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Colville, Kevin. "An analysis of frictional effects in non-stationary contact problems for metal forming simulations". Doctoral thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33435.
Testo completoAbstract (sommario):
The finite element method (FEM) is widely used for the simulation of metal forming processes and has been successfully used in contact problems which arise in processes such as deep-drawing, punching, extrusion and rolling. All these processes involve friction between the contact surfaces: the sheet-metal workpiece and the toolpieces. The model of friction is thus an important part of any simulation of metal forming processes. Most FEM codes use a friction model that assumes that the contact surface is a plane. Attempts to address this problem have focused on the convective description of deformation, which has the advantage of being naturally extended to numerical methods like the FEM at the expense of additional computation and numerical complexity. The convective description is used in this work, which focuses on the numerical implementation of the objective measure. The effects of the rotation of the material contact point is taken into account by including objective time derivatives of the slipping (tangential) direction function. The objective rate of the direction function includes the surface spin induced by the rigid motion of a contact point sliding over the tool surface, and the material spin occurring during the elastic-plastic deformation of the blank. This is introduced by adapting the incremental relations of the friction slip. This thesis presents the results of numerical experiment to determine the influence that the rotation and convection of contact points has on the frictional stresses and slipping energy. Four different friction models are implemented within the finite element program ABAQUS and applied to simulations of standardmetal forming benchmark processes: the square-cup and s-rail deep drawing benchmarks of the Numisheet conferences, for which several experimental and numerical results are available to compare with the solution of a finite element simulation. The results for each metal-forming simulation are calculated for different friction models, and are compared and a choice made as to which is the “best” friction model for the process. Further, the reverse problem of determining the values of friction parameters by comparison of simulation and experimental results is performed for these benchmark problems. As there is yet no ideal friction model for all processes that are modelled, finding the most appropriate friction model by numerical means is proposed to improve the quality of a simulation.
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Silva, Raquel Cristina Soares de Carvalho e. "Development of numerical methodologies for parameter identification and shape optimization in metal forming simulations". Doctoral thesis, Universidade de Aveiro, 2012. http://hdl.handle.net/10773/11202.
Testo completoAbstract (sommario):
Doutoramento em Engenharia MecânicaPor parte da indústria de estampagem tem-se verificado um interesse crescente em simulações numéricas de processos de conformação de chapa, incluindo também métodos de engenharia inversa. Este facto ocorre principalmente porque as técnicas de tentativa-erro, muito usadas no passado, não são mais competitivas a nível económico. O uso de códigos de simulação é, atualmente, uma prática corrente em ambiente industrial, pois os resultados tipicamente obtidos através de códigos com base no Método dos Elementos Finitos (MEF) são bem aceites pelas comunidades industriais e científicas Na tentativa de obter campos de tensão e de deformação precisos, uma análise eficiente com o MEF necessita de dados de entrada corretos, como geometrias, malhas, leis de comportamento não-lineares, carregamentos, leis de atrito, etc.. Com o objetivo de ultrapassar estas dificuldades podem ser considerados os problemas inversos. No trabalho apresentado, os seguintes problemas inversos, em Mecânica computacional, são apresentados e analisados: (i) problemas de identificação de parâmetros, que se referem à determinação de parâmetros de entrada que serão posteriormente usados em modelos constitutivos nas simulações numéricas e (ii) problemas de definição geométrica inicial de chapas e ferramentas, nos quais o objetivo é determinar a forma inicial de uma chapa ou de uma ferramenta tendo em vista a obtenção de uma determinada geometria após um processo de conformação. São introduzidas e implementadas novas estratégias de otimização, as quais conduzem a parâmetros de modelos constitutivos mais precisos. O objetivo destas estratégias é tirar vantagem das potencialidades de cada algoritmo e melhorar a eficiência geral dos métodos clássicos de otimização, os quais são baseados em processos de apenas um estágio. Algoritmos determinísticos, algoritmos inspirados em processos evolucionários ou mesmo a combinação destes dois são usados nas estratégias propostas. Estratégias de cascata, paralelas e híbridas são apresentadas em detalhe, sendo que as estratégias híbridas consistem na combinação de estratégias em cascata e paralelas. São apresentados e analisados dois métodos distintos para a avaliação da função objetivo em processos de identificação de parâmetros. Os métodos considerados são uma análise com um ponto único ou uma análise com elementos finitos. A avaliação com base num único ponto caracteriza uma quantidade infinitesimal de material sujeito a uma determinada história de deformação. Por outro lado, na análise através de elementos finitos, o modelo constitutivo é implementado e considerado para cada ponto de integração. Problemas inversos são apresentados e descritos, como por exemplo, a definição geométrica de chapas e ferramentas. Considerando o caso da otimização da forma inicial de uma chapa metálica a definição da forma inicial de uma chapa para a conformação de um elemento de cárter é considerado como problema em estudo. Ainda neste âmbito, um estudo sobre a influência da definição geométrica inicial da chapa no processo de otimização é efetuado. Este estudo é realizado considerando a formulação de NURBS na definição da face superior da chapa metálica, face cuja geometria será alterada durante o processo de conformação plástica. No caso dos processos de otimização de ferramentas, um processo de forjamento a dois estágios é apresentado. Com o objetivo de obter um cilindro perfeito após o forjamento, dois métodos distintos são considerados. No primeiro, a forma inicial do cilindro é otimizada e no outro a forma da ferramenta do primeiro estágio de conformação é otimizada. Para parametrizar a superfície livre do cilindro são utilizados diferentes métodos. Para a definição da ferramenta são também utilizados diferentes parametrizações. As estratégias de otimização propostas neste trabalho resolvem eficientemente problemas de otimização para a indústria de conformação metálica.
The interest of the stamping industry in the numerical simulation of sheet metal forming, including inverse engineering approaches, is increasing. This fact occurs mainly because trial and error design procedures, commonly used in the past, are no longer economically competitive. The use of simulation codes is currently a common practice in the industrial forming environment, as the results typically obtained by means of the Finite Element Method (FEM) are well accepted by both the industrial and scientific communities. In order to obtain accurate stress and strain fields, an effective FEM analysis requires reliable input data such as geometry, mesh, non-linear material behaviour laws, loading cases, friction laws, etc.. In order to overcome these difficulties, a possible approach is based on inverse problems. In this work, the following inverse problems in computational Mechanics are presented and analysed: (i) parameter identification problem, that refer to the definition of input parameters to be used in constitutive models for numerical simulations, based on experimental data, and (ii) initial blank and tool design problem, where the aim would be to estimate the initial shape of a blank or a tool in order to achieve the desired geometry after the forming process. New optimization strategies in parameter identification problems that lead more efficiently to accurate material parameters are introduced and implemented. The aim of these strategies is to take advantage of the strength of each selected algorithm and improve the overall robustness and efficiency of classical optimization methodologies based on single stages. Deterministic algorithms, evolutionary-inspired algorithms or even the combination of these two algorithms are used in the proposed strategies. Strategies such as cascade, parallel and hybrid approaches are analysed in detail. In hybrid strategies, cascade and parallel approaches are integrated. Two different approaches are presented and analyzed for the evaluation of the objective functions in parameter identification processes. The approaches considered are single-point and FE analyses. The single infinitesimal point evaluation seems to characterize an infinitesimal amount of material subjected to all kind of deformation history. On the other hand, in all FE analysis codes, the constitutive model is implemented and accounted for in each element integration point. Inverse problems, such as blank and tool design, are presented and described. In the case of the initial blank optimization process the design of a carter is presented. Also related to the initial blank optimization process, a study of the influence of the initial geometry definition in the optimization process is conducted. This study is performed considering the NURBS formulation to model the blank upper surface that will be changed during the optimization process. In the case of the tool design problem, a two-stage forging process is presented. In order to achieve a straight cylinder after forging, two different approaches are analyzed. In the first one, the initial geometry of the cylinder is optimized and, in the other one, the shape of the first stage tool is optimized. To parameterize the free surface of the cylinder different methods are presented. Furthermore, in order to define the tool in this example, different parameterizations are presented. The optimisation strategies proposed in this work efficiently solve optimisation problems for the industrial metal forming.
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nilsson, Kevin. "Material modeling in Sheet Metal Forming Simulations : Quality comparison between comonly used material models". Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-18227.
Testo completoAbstract (sommario):
In today's automotive industries, many different simulation programs are used to optimize parts before they come into production. This has created a market for complex material models to get the best possible approximation of reality in the simulation environment. Several industries are still using older material models that can’t give an acceptable accuracy for the materials currently in use as they are based on much simpler and older materials. The problem with material models is that there is no direct comparison between the material models which leads to several sheet metal forming companies still holding on to older models like Hill`48. The purpose of this work is to create a comparison of sheet material models from a user perspective to be able to provide recommendations of material models. Different models will be tested for different materials and will be based on AutoForm's recommendations. AutoForm is a FEM based sheet metal forming simulation program used by large names in the automotive industry. These recommendations are Vegter2017, BBC2005 or Hill`48 for steel and Vegter2017, BBC2005 or Barlat`89 for aluminum. This work is achieved by comparing experimental data from a Limiting Dome Height (LDH) test with a simulation of this test for all material models and then comparing the results. The data that will be compared consists of the major and minor strain in the sheet as well as the punch force. These parameters are chosen as they give an overview of the model’s applicability as well as accuracy. The test will be performed on all materials available in Volvo Cars material library to create a broader overview of all material models. The material models will also be evaluated depending on their user-friendliness by analyzing what types of data are required to perform a simulation. The result from these tests showed that BBC 2005 should be recommended for aluminum and steel for companies that have access to biaxial data and for people who put optimization in focus. Hill`48 proved far too deviant in the results for steel and should not be used if other models are available. Vegter 2017 proved perfect for steel simulations as the result were great as well as the necessary material data can be obtained through standardized tensile tests. The result also showed that Vegter2017 should not be used for aluminum since the result was too deviant from the experimental data in aspect for both form approximation and strain magnitude. Barlat`89 gave accurate results with only data from a tensile test which makes it a preferred model when working with aluminum. The conclusion from this work is that the choice of material model is very dependent on what conditions you have as very few industries have access to the tests required by the BBC 2005 model. Another conclusion may be drawn for Barlat`89 with aluminum and Vegter 2017 with steel as they can be preferred when working with a small timeframe as well as when few test data is available.Inom dagens bilindustri används det många olika simuleringsprogram för att optimera delar innan de kommer ut i produktion. Detta har då skapat en marknad för komplexa material modeller för att få en så bra approximation av verkligheten som möjligt. I flera industrier använder man sig fortfarande av äldre materialmodeller som egentligen inte håller måttet för dagens material då de är baserade på simplare material. Problemet som har skapat denna situation är att det inte direkt finns en konkret jämförelse mellan materialmodellerna vilket leder till att flera plåtformnings företag fortfarande håller kvar vid äldre modeller som t e x Hill`48. Syftet med detta arbete är att skapa en jämförelse av plåt materialmodeller från ett användarperspektiv för att kunna ge konkreta bevis till rekommendationer av materialmodeller. Olika modeller skall testas för olika material och baseras på AutoForms rekommendationer. AutoForm är ett FEM baserat plåtformningssimulerings program som används av stora namn inom bilindustrin. Dessa rekommendationer är då att köra Vegter2017, BBC2005 eller Hill`48 för stål samt att köra Vegter2017, BBC2005 eller Barlat`89 för aluminium. Detta arbete utförs genom att jämföra experimentella data från ett Limiting Dome Height (LDH) test med en simulering av detta test för alla material modeller och sedan jämföra resultaten. Jämförelsen mellan den experimentella och simuleringsdatan kommer att involvera major och minor strain i plåten samt stämpelkraften. Dessa parametrar har valts då de ger en bra översikt över materialmodellernas applicerbarhet och noggrannhet. Testen kommer att utföras på samtliga material som finns tillgängliga i Volvo Cars materialbibliotek för att skapa en breddare syn på samtliga modellers applicerbarhet. Materialmodellerna kommer även att utvärderas beroende på deras användarvänlighet samt vilka typer av data krävs för att använda modellen. Resultatet visade att BBC 2005 skall rekommenderas för aluminium samt stål till de företag som har tillgång till biaxiella data samt lägger optimering i fokus. Hill`48 visade sig alldeles för avvikande för stål och bör inte användas om andra modeller är tillgängliga. Vegter 2017 visade sig perfekt för stål då resultatet var bra samt att den nödvändiga materialdatan kan införskaffas genom standardiserade dragprov. Resultatet visade även att Vegter 2017 inte bör användas för aluminium då resultatet var för avvikande. Barlat`89 gav bra resultat med endast data från dragprovstest vilket ger att den är att rekommendera för aluminium. Slutsatsen från detta arbete är att valet av materialmodell är väldigt beroende av vilka förutsättningar som finns då väldigt få industrier har tillgång till de tester som krävs för att använda BBC 2005. I större delar av industrin där minimala optimeringar inte anses som väsentliga är Barlat`89 och Vegter 2017 att föredra då detta leder till snabbare processer.
15
Sansalone, Mickaël. "A new shell formulation using complete 3D constitutive laws : Applications to sheet metal forming simulations". Thesis, Lyon, INSA, 2011. http://www.theses.fr/2011ISAL0015.
Testo completoAbstract (sommario):
Dans le domaine de la mise en forme industrielle, des outils de simulation comme le logiciel Pam-stamp 2G permettent entre autres le prototypage et l’optimisation numérique des produits, réduisant ainsi les coûts expérimentaux de mise au point. Les éléments finis de type coques en hypothèse d’état plan de contrainte demeurent les plus utilisés car ils permettent une prise en compte réaliste des déformations majeures de membrane et de flexion. Cependant, de par leur définition, la contrainte normale pouvant apparaitre en cas de compression du flan dans la direction de l’épaisseur ou encore de flexion extrême sur petit rayon est systématiquement omise. De plus, Il existe de nouveaux procédés de mise en forme de tôle, comme le pliage/sertissage/emboutissage avec laminage et/ou écrasement ainsi que l’hydroformage, qui ne peuvent pas être traités avec ces formulations d’éléments coques classiques. L’utilisation de couches d’éléments volumiques est souvent considérée comme une alternative non convenable aux simulations de ces procédés. Outre le très haut coût CPU, s’ajoutent le rendu parfois non réaliste ainsi que la complexité liée à la découpe du maillage du flan. Récemment, des éléments de type “solid-shell” ont été mis à contribution mais requièrent des améliorations quant à leurs lois de comportements. L’objectif d’ESI group consiste en l’élaboration, l’évaluation, l’implémentation et la validation industrielle d’une nouvelle formulation d’élément fini. Cet élément devra permettre la gestion d’une éventuelle variation d’épaisseur avec prise en compte réaliste de la contrainte normale, tout en assurant des résultats dignes de ceux d’une coque conventionnelle en flexion. Une nouvelle formulation de type coque 3D est ainsi d’abord proposée. Des éléments coques triangulaires et quadrangulaire en théorie de Mindlin et de Kirchhoff sont utilisés. Cette approche est d’abord développée dans un solveur quasi-statique implicite de l’INSA de Lyon pour validation numérique sur cas académiques linéaires et non linéaires de référence. Une validation expérimentale sur opération de pliage dépliage est également réalisée. Aux vues des non linéarités dues au contact avec frottement, grandes déformations et grands déplacements posant des soucis de convergence en implicite au cours de la simulation d’opérations de mise en forme, la méthode est ensuite développée dans le solveur explicite de l’INSA de Lyon. Seuls les éléments en théorie de Mindlin sont considérés. Les particularités liées à cette méthode de résolution dynamique comme la matrice de masse, le pas de temps critique et l’optimisation du CPU sont traitées. Une nouvelle méthode de contact dédiée aux opérations de mise en forme impliquant du laminage et/ou de l’amincissement est également proposée. Elle permet une transition automatique d’éléments standards vers des éléments coque "3D", palliant ainsi le remaillage. Des essais de mise en forme en U avec ou sans laminage apportent une validation expérimentale concernant le retour élastique. Une fois validées, les techniques et formulations les plus abouties sont implémentées dans le code industriel dédié à la mise en forme Pam-stamp 2G v2011. Après une vérification sur tests de référence, des applications sont enfin menées sur cas critiques inspirés de procédés industriels complexes et nécessitant essentiellement une loi de comportement 3DIn the sheet metal forming industry, shell elements in plane-stress assumption are employed, as they perform quite well in simulating the major membrane and flexural large deformations involved. However, the normal stress, caused by compression along thickness direction of the blank or local high bending over very small radii, is hence systematically omitted. Besides, when it comes to unusual and challenging processes such as hydro-forming, thinning/thickening, forming with ironing, bottoming and so on, makeshift solutions such as layers of 3D solid hexahedrons or even recent “solid-shell” elements are no longer appropriate. An innovative 3D finite element formulation methodology overcoming the overcoming the plane-stress definition of classification shell elements, while keeping their very good bending assets is first proposed in this work. The method basically consists in adding a central node endowed with two degrees of freedom at the element center. These two extra translations normal to the element mid-plane give a new quadratic displacement field along the shell normal direction. A derivative normal strain can hence be expressed and a linear normal stress comes via a full 3D constructive law. A very pioneering contact technique, dedicated to forming processes with ironing, thinning/bottoming operations and allowing a usual-to-enhanced automatic element switch is developed as well. Once widely assessed, most interesting achievements are implemented in the dynamic explicit industrial code Pam-stamp 2 G v2011 and evaluated over critical industrial forming processes that require essentially a full 3D strain-stress behavior
16
Schmeja, Stefan. "Properties of turbulent star forming clusters: models versus observations". Phd thesis, [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980518660.
Testo completo
17
Tatipala, Sravan. "Sheet metal forming in the era of industry 4.0 : using data and simulations to improve understanding, predictability and performance". Licentiate thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-18954.
Testo completoAbstract (sommario):
A major issue within automotive Sheet Metal Forming (SMF) concerns ensuring desired output product quality and consistent process performance. This is fueled by complex physical phenomena, process fluctuations and complicated parameter correlations governing the dynamics of the production processes. The aim of the thesis is to provide a deeper understanding of the challenges and opportunities in this regard within automotive SMF. The research is conducted in collaboration with a global automotive manufacturer. The research shows that systematic investigations using process simulation models allow exploration of the product-process parameter interdependencies and their influence on the output product quality. Furthermore, it is shown that incorporating in-line measured data within process simulation models enhance model prediction accuracy. In this regard, automating the data processing and model configuration tasks reduces the overall modelling effort. However, utilization of results from process simulations within a production line requires real-time computational performance. The research hence proposes the use of reduced process models derived from process simulations in combination with production data, i.e. a hybrid data- and model-based approach. Such a hybrid approach would benefit process performance by capturing the deviations present in the real process while also incorporating the enhanced process knowledge derived from process simulations. Bringing monitoring and control realms within the production process to interact synergistically would facilitate the realization of such a hybrid approach. The thesis presents a procedure for exploring the causal relationship between the product-process parameters and their influence on output product quality in addition to proposing an automated approach to process and configure in-line measured data for incorporation within process simulations. Furthermore, a framework for enhancing output product quality within automotive SMF is proposed. Based on the thesis findings, it can be concluded that in-line measured data combined with process simulations hold the potential to unveil the convoluted interplay of process parameters on the output product quality parameters.Related work:
1) http://urn.kb.se/resolve?urn=urn:nbn:se:bth-14412
2) http://urn.kb.se/resolve?urn=urn:nbn:se:bth-14388
3) http://urn.kb.se/resolve?urn=urn:nbn:se:bth-18935
18
Coslovich, Daniele. "Connections between structure,dynamics and energy landscape in simple models of glass-forming liquids". Doctoral thesis, Università degli studi di Trieste, 2008. http://hdl.handle.net/10077/2563.
Testo completoAbstract (sommario):
2006/2007The microscopic origin of the glass-transition represents a long-standing open problem in condensed matter physics. Recent theoretical advances and the increasing amount of experimental and simulation data demonstrate the activity of this field of research. In this thesis we address, through molecular dynamics simulations of model glass-forming liquids, a key and yet unsolved issue concerning the description of the glass-transition: the connection between the unusual dynamical properties of glass-formers, their structural properties, and the features of the intermolecular interactions. Toward this end, we consider a broad range of models based on pair interactions. Such models are able to describe both fragile and strong glass-formers and to reproduce different types of local order, including icosahedral and prismatic structures (typical of metallic glasses) as well as tetrahedral ones (typical of network glasses). For these models we provide a systematic characterization of the structure, dynamics, and potential energy surface. The first part of the thesis briefly introduces the theoretical framework concerning the connection between structure and dynamics in fragile and strong glass-formers, as well as the main experimental and simulation results. The state of the art of the description in terms of the potential energy surface is critically reviewed on the basis of recent simulation results. The simulation methods and the optimization algorithms employed in the thesis are then presented, focusing on the stage of object-oriented analysis of the problem of molecular simulations of classical interacting systems. Such analysis constitutes an original aspect of the thesis and provided a unified and effective framework for the development of simulation software. The second part focuses on the main results obtained. The variations of dynamical properties in different systems, with particular reference to the Angell's fragility and to dynamic heterogeneities, are traced back first to the features of the locally preferred structures, then to the properties of the potential energy surface. In particular, we show that the variation of fragility in the models considered can be rationalized in terms of the formation of stable domains formed by locally preferred structures. The analysis of the properties of stationary points (local minima and saddle points) in the potential energy surface allows us to establish a direct connection between fragility, structurally stable domains and energy barriers. On the other hand, the spatial localization features of the unstable modes display qualitative variations in the models considered. The study of the correlation between the spatial localization of the unstable modes and the propensity of motion reveals that the dynamical influence of such modes is typical of the late beta-relaxation - time scale within which the effect of dynamic heterogeneity is maximum. It appears to be easier to identify such connection in fragile, rather than strong, systems. This provides indications on the possible qualitative differences concerning the metabasin structure of the potential energy surface in fragile and strong glass-formers.
XX Ciclo
1980
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Aykol, Muratahan. "Nano-scale Phase Separation And Glass Forming Ability Of Iron-boron Based Metallic Glasses". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609825/index.pdf.
Testo completoAbstract (sommario):
This study is pertinent to setting a connection between glass forming ability (GFA) and topology of Fe-B based metallic glasses by combining intimate investigations on spatial atomic arrangements conducted via solid computer simulations with experimentations on high GFA bulk metallic glasses. In order to construct a theoretical framework, the nano-scale phase separation encountered in metallic glasses is investigated for amorphous Fe80B20 and Fe83B17 alloys via Monte Carlo equilibration and reverse Monte Carlo simulation. The phenomenon is identified regarding three topological aspects: 1) Pure Fe-clusters as large as ~0.9 nm and Fe-contours with ~0.72 nm thickness, 2) Fe-rich highly deformed body centered cubic regions, 3) B-centered prismatic units with polytetrahedral order forming distinct regions of high and low coordinations are found. All topological aspects are compiled into a new model called Two-Dimensional Projection Model for predicting contributions to short and medium range order (MRO) and corresponding spacing relations. The outcome geometrically involves proportions approximating golden ratio. After successfully producing soft magnetic Fe-Co-Nb-B-Si based bulk metallic glass and bulk nanocrystalline alloys with a totally conventional route, influences of alloying elements on structural units and crystallization modes are identified by the developed model and radial distributions. While Co atoms substitute for Fe atoms, Nb and Si atoms deform trigonal prismatic units to provide local compactions at the outset of MRO. Cu atoms alter the type of MRO which resembles crystalline counterparts and accompanying nanocrystals that precipitate. The GFA can be described by a new parameter quantifying the MRO compaction, cited as Φ
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Lindström, Stefan B. "Simulations of the Dynamics of Fibre Suspension Flows". Licentiate thesis, Mid Sweden University, Department of Natural Sciences, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-53.
Testo completoAbstract (sommario):
A new model for simulating non-Brownian flexible fibres suspended in a Newtonian fluid has been developed. Special attention has been given to include realistic flow conditions found in the industrial papermaking process in the key features of the model; it is the intention of the author to employ the model in simulations of the forming section of the paper machine in future studies.
The model considers inert fibres of various shapes and finite stiffness, interacting with each other through normal, frictional and lubrication forces, and with the surrounding fluid medium through hydrodynamic forces. Fibre-fluid interactions in the non-creeping flow regime are taken into account, and the two-way coupling between the solids and the fluid phase is included by enforcing momentum conservation between phases. The incompressible three-dimensional Navier-Stokes equations are employed to model the motion of the fluid medium.
The validity of the model has been tested by comparing simulation results with experimental data from the literature. It was demonstrated that the model predicts the motion of isolated fibres in shear flow over a wide range of fibre flexibilities. It was also shown that the model predicts details of the orientation distribution of multiple straight, rigid fibres in a sheared suspension. Model predictions of the viscosity and first normal stress difference were in good agreement with experimental data found in the literature. Since the model is based solely on first-principles physics, quantitative predictions could be made without any parameter fitting.
En ny modell för simulering av rörelserna hos icke-Brownska böjliga fibrer dispergerade i en Newtonsk vätska har utvecklats. Eftersom det är författarens avsikt att modellen skall kunna tillämpas vid simulering av arkformning under de förhållanden som råder i en modern pappersmaskin, har särskilt omsorg givits till att inkludera motsvarande flödesvillkor i modellens giltighetsområde.
Modellen hanterar fibrer av varierande form, massa och styvhet, som växelverkar sinsemellan via normal-, friktions- och smörjkrafter. Deras växelverkan med den omgivande vätskan sker via hydrodynamiska krafter vid finita Reynolds-tal. Den så kallade tvåvägskopplingen mellan fibrerna och vätskefasen har tagits i beaktande genom att kräva att rörelsemängden bevaras vid interaktionen mellan faserna. Vidare har Navier-Stokes ekvationer för inkompressibla vätskor använts för att beskriva mediets rörelser.
Modellens giltighet har undersökts genom att jämföra resultat från simuleringar med experimentella data från litteraturen. Det har påvisats att modellen förutsäger rörelsen hos ensamma fibrer i ett skjuvflöde, för vitt skilda fiberflexibiliteter. Det visades också att modellen förutsäger detaljer hos fiberorienteringsdistributionen i suspensioner utsatta för skjuvflöde. Det kunde också konstateras att modellens förutsägelser av fibersuspensioners viskositet och första normalspänningsdifferens under skjuvning väl överensstämde med experimentella data i litteraturen. Kvantitativa förutsägelser har kunnat göras utan någon parameteranpassning, då modellen bygger uteslutande på väletablerade fysikaliska samband inom klassisk mekanik och strömningslära.
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Xenos, Sokratis. "Porous materials : constitutive modeling and computational issues". Electronic Thesis or Diss., Institut polytechnique de Paris, 2024. http://www.theses.fr/2024IPPAX040.
Testo completoAbstract (sommario):
Ce travail porte sur le développement, la calibration et l'implémentation numérique d'un nouveau modèle élastoplastique entièrement explicite, isotrope et indépendant du taux de déformation pour les matériaux métalliques poreux. La microstructure est supposée être constituée d'une distribution aléatoire de vides sphéroïdaux de même forme, orientés de manière aléatoire et avec une probabilité uniforme. Le modèle proposé est basé sur des estimations d'homogénéisation antérieures qui utilisent une théorie de comparaison composite linéaire (LCC). Pour évaluer l'exactitude du modèle analytique, nous réalisons des simulations éléments finis tridimensionnelles à grandes déformationsd'éléments de volume représentatifs (RVE) avec les microstructures correspondantes. Une calibration appropriée des paramètres du modèle conduit à un accord assez précis des prédictions analytiques avec les contraintes moyennes éléments finis et l'évolution de la porosité. Nous montrons, à la fois analytiquement et numériquement, que le rapport d'aspect initial des vides a un effet significatif sur la réponse effective homogénéisée du matériau poreux, entraînant des réponses extrêmement souples pour les vides très oblates, surtout à des triaxialités de contraintes élevées.Ensuite, nous examinons les problèmes computationnels liés à l'implémentation numérique de modèles constitutifs indépendants du taux de déformation qui conduisent à un comportement d'adoucissement. Il est démontré analytiquement que les modèles élastoplastiques basés sur des formulations continues "locales'' peuvent entraîner une perte d'ellipticité des équations aux dérivées partielles (EDP) et des solutions numériques dépendantes du maillage. Pour remédier les problèmes numériques associés, nous proposons une version implicite non locale du nouveau modèle poreux, basée sur l'introduction d'une variable de porosité non locale déterminée à partir de la solution d'une EDP supplémentaire. Nous montrons à la fois analytiquement et numériquement que la version régularisée du modèle permet de préserver les propriétés elliptiques des équations du problème, produisant des solutions convergentes indépendantes du maillage dans le régime post-bifurcation. Le point de bifurcation s'avère être fortement dépendant de la forme des micro-vides, avec des vides très plats (par exemple,un rapport d'aspect inférieur à 0,3) entraînant des déformations à la localisation plus faibles. Il est constaté que la longueur matérielle introduite par la formulation non locale a un effet minimal sur le point de bifurcation prédit, affectant uniquement le gradient post-bifurcation de la courbe contrainte-déformation macroscopique et la taille de lazone fortement déformée dans la structure. Dans la dernière partie de cette étude, les versions locale et non locale du modèle sont efficacement implémentées dans un code commercial d'éléments finis (ABAQUS) et utilisés pour la solution numérique de problèmes de valeurs limites liés aux processus de formage et de rupture ductile. En particulier, les problèmes de test d'expansion de trou (TET) et de test d'impact Charpy (essai Charpy), le phénomène de rupture "cup-and-cone'' ainsi que la rupture ductile d'un spécimen à géométrie complexe et la comparaison avec les résultats expérimentaux correspondants sont analysés en détail. Les prédictions numériques indiquent que la ductilité est une fonction croissante du paramètre de forme des vides, et les matériaux composés de vides oblates de faible rapport d'aspect présentent une initiation et une propagation macroscopiques de fissures prématurées par rapport aux matériaux avec des vides sphériques ou presquesphériques. Enfin, la capacité du modèle à reproduire les résultats expérimentaux avec une précision suffisante suggère qu'il peut être utilisé pour fournir des prédictions avec seulement un petit nombre de paramètres qui peuvent être calibrés à partir de calculs micromécaniques ou de données expérimentalesThis work is concerned with the development, calibration, and numerical implementation of a novel fully explicit isotropic, rate-independent, elasto-plastic model for porous metallic materials. The microstructure is assumed to consist of a random, with uniform probability, distribution of randomly oriented spheroidal voids of the same shape. The proposed model is based on earlier homogenization estimates that use a Linear Comparison Composite (LCC) theory. The resulting expressions exhibit the simplicity of the well known Gurson model and, thus, its numerical implementation in a finite element code is straightforward. To assess the accuracy of the analytical model, we carry out detailed finite-strain, three-dimensional finite element (FE) simulations ofrepresentative volume elements (RVEs) with the corresponding microstructures. Properparameter calibration of the model leads to fairly accurate agreement of the analytical predictions with the corresponding FE average stresses and porosity evolution. We show, both analytically and numerically, that the initial aspect ratio of the voids has a significant effect on the homogenized effective response of the porous material leading to extremely soft responses for flat oblate voids (e.g., aspect ratio less than 0.5) especially at high stress triaxialities.Next, we examine the computational issues related to the numerical implementation of rate-independent constitutive models that lead to softening behavior. It is shown analytically that elastic-plastic models based on ``local'' continuum formulations that do not incorporate a characteristic length scale may lead to loss of ellipticity of the governing partial differential equations (PDEs) and mesh-dependent numerical solutions. To remedy the associated numerical problems, we propose an implicit non-local version of the porous model developed in this work which is based on the introductionof a non-local porosity variable determined from the solution of an additional PDE. We show both analytically and numerically that the regularized version of the model allows for preservation of the elliptic properties of the governing equations yielding mesh-independent, converged solutions in the post-bifurcation regime. The bifurcation point (i.e., strain-to-localization) is found to be highly dependent on the micro-void's shape, with very flat voids (e.g., aspect ratio less than 0.3) leading to lower localization strains. The material length introduced by the non-local formulation is found tohave minimal effect on the predicted bifurcation point, only affecting the post-bifurcation gradient of the macroscopic stress-strain curve and the size of the highly strained zone in the structure.In the last part of this study, both the local and the non-local versions of the model are efficiently implemented in a commercial finite element code (ABAQUS). The models are used for the numerical solution of boundary value problems (BVPs) related to forming and ductile fracture processes under both quasi-static and dynamic conditions. In particular, the industrially relevant problems of Hole expansion (HET) and Charpy impact (CVN) test, the cup-and-cone fracture phenomenon as well as ductile fracture of a specimen with complex geometry and comparison with corresponding experimentalresults are analyzed in detail. Numerical predictions in all cases indicate that ductility is an increasing function of the void shape parameter and materials comprising flat oblate voids of low aspect ratio exhibit early macroscopic crack initiation and propagation compared to materials with spherical/almost spherical voids. Finally, the model's capability to reproduce experimental results with sufficient accuracy suggests that it can be utilized to provide predictions with only a small amount of parameters that may be calibrated from either micromechanics calculations or experimental data
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Matthes, Dirk [Verfasser], Bert de [Akademischer Betreuer] Groot e Hansjörg [Akademischer Betreuer] Abel. "Spontaneous aggregation of fibril-forming peptides studied by Molecular Dynamics simulations / Dirk Matthes. Gutachter: Hansjörg Abel ; Bert de Groot. Betreuer: Bert de Groot". Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2012. http://d-nb.info/1043025537/34.
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Vi, Frédéric. "Methode multigrilles parallèle pour les simulations 3D de mise en forme de matériaux". Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEM009/document.
Testo completoAbstract (sommario):
Cette thèse porte sur le développement d’une méthode multigrilles parallèle visant à réduire les temps de calculs des simulations éléments finis dans le domaine de la mise en forme de pièces forgées en 3D. Ces applications utilisent une méthode implicite, caractérisées par une formulation mixte en vitesse/pression et une gestion du contact par pénalisation. Elles impliquent de grandes déformations qui rendent nécessaires des remaillages fréquents sur les maillages tétraédriques non structurés utilisés. La méthode multigrilles développée suit une approche hybride, se basant sur une construction géométrique des niveaux grossiers par déraffinement de maillage non emboîtés et sur une construction algébrique des systèmes linéaires intermédiaires et grossiers. Un comportement asymptotique quasi-linéaire et une bonne efficacité parallèle sont attendus afin de permettre la réalisation de simulations à grand nombre de degrés de liberté dans des temps plus raisonnables qu’aujourd’hui. Pour cela, l’algorithme de déraffinement de maillages est compatible avec le calcul parallèle, ainsi que les opérateurs permettant les transferts de champs entre les différents niveaux de maillages partitionnés. Les spécificités des problèmes à traiter ont mené à la sélection d'un lisseur plus complexe que ceux utilisés plus fréquemment dans la littérature. Sur la grille la plus grossière, une méthode de résolution directe est utilisée, en séquentiel comme en calcul parallèle. La méthode multigrilles est utilisée en tant que préconditionneur d’une méthode de résidu conjugué et a été intégrée au logiciel FORGE NxT et montre un comportement asymptotique et une efficacité parallèle proches de l’optimal. Le déraffinement automatique de maillages permet une compatibilité avec les remaillages fréquents et permet à la méthode multigrilles de simuler un procédé du début à la fin. Les temps de calculs sont significativement réduits, même sur des simulations avec des écoulements particuliers, sur lesquelles la méthode multigrilles ne peut être utilisée de manière optimale. Cette robustesse permet, par exemple, de réduire de 4,5 à 2,5 jours le temps de simulation d’un procédéA parallel multigrid method is developed to reduce large computational costs involved by the finite element simulation of 3D metal forming applications. These applications are characterized by a mixed velocity/pressure implicit formulation with a penalty formulation to enforce contact and lead to large deformations, handled by frequent remeshings of unstructured meshes of tetrahedral. The developed multigrid method follows a hybrid approach where the different levels of non-nested meshes are geometrically constructed by mesh coarsening, while the linear systems of the intermediate and coarse levels result from the algebraic approach. A close to linear asymptotical behavior is expected along with parallel efficiency in order to allow simulations with large number of degrees of freedom under reasonable computation times. These objectives lead to a parallel mesh coarsening algorithm and parallel transfer operators allowing fields transfer between the different levels of partitioned meshes. Physical specificities of metal forming applications lead to select a more complex multigrid smoother than those classically used in literature. A direct resolution method is used on the coarsest mesh, in sequential and in parallel computing. The developed multigrid method is used as a preconditioner for a Conjugate Residual algorithm within FORGE NxT software and shows an asymptotical behavior and a parallel efficiency close to optimal. The automatic mesh coarsening algorithm enables compatibility with frequent remeshings and allows the simulation of a forging process from beginning to end with the multigrid method. Computation times are significantly reduced, even on simulations with particular material flows on which the multigrid method is not optimal. This robustness allows, for instance, reducing from 4.5 to 2.5 days the computation of a forging process
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Uran, Matthias [Verfasser], Axel [Gutachter] Klawonn, Oliver [Gutachter] Rheinbach e Jörg [Gutachter] Schröder. "High-Performance Computing Two-Scale Finite Element Simulations of a Contact Problem Using Computational Homogenization - Virtual Forming Limit Curves for Dual-Phase Steel / Matthias Uran ; Gutachter: Axel Klawonn, Oliver Rheinbach, Jörg Schröder". Köln : Universitäts- und Stadtbibliothek Köln, 2020. http://d-nb.info/1215837089/34.
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Hellborg, Simon. "Finite Element Simulation of Roll Forming". Thesis, Linköping University, Department of Management and Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8312.
Testo completoAbstract (sommario):
A finite element model has been developed to simulate the forming of a channel section profile with the roll forming method. The model has been optimized to experimental results with respect to strains at the edge of the sheet and spring back of the sides of the profile. Finite element models with a coarse mesh have been compared to models with a finer mesh. The models with to fine mesh become instable and a model with a rather coarse mesh was finally chosen.
Both the models with shell elements and the models with solid elements have been used in the simulations. The simulations with shell elements gave very good results both for the geometry shape and the strains at the edge of the sheet. The reaction forces at the tools found in the simulations was only half of the reaction forces fond in the experiments.
The simulations with the solid element model showed very good results for the reaction forces while the geometry shape of the sheet was really bad. The spring back was much larger in the simulations than in the experiments.
The shell element model was chosen because of the excessive spring back with the solid element model. The spring back of the sides of the sheet differs only a few percent between the simulation and the experiment results when using the shell element model. The reaction forces at the tools in the simulation are only half of the reaction forces measured in the experiments but the results from the simulations are linearly proportional to the results in the experiments. The model that finally was chosen describe both the spring back and the strains at the edge of the sheet very well. Like in the experiments there were no signs of wrinkles at the sheet in any of the simulations.
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Oganov, Artem Romaevich. "Computer simulation studies of minerals". Thesis, University College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271656.
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Zhuang, Shoubing. "Enhancing Implicit Finite Element Sheet Forming Simulation". The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1206124132.
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Wu, Wei-Tsu. "AMG : automated mesh generation for forming simulation /". The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487686243822162.
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Duggal, Nitin. "Process Simulation of Roll Forming and Roll Pass Design". Connect to this title online, 1995. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1105385307.
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Lindgren, Michael. "Modelling and simulation of the roll forming process /". Luleå : Luleå University of Technology, 2005. http://epubl.luth.se/1402-1757/2005/040.
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Chen, Shuai. "Fabric forming simulation and process optimisation for composites". Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/38522/.
Testo completoAbstract (sommario):
The development and optimisation of automated fabric preforming processes is critical for the adoption of composite materials for low cost, high volume applications. This thesis presents the development of a numerical material model to simulate the forming of 2D fabric plies into complex 3D shapes. The material model has been used to evaluate the feasibility of using matched-tool forming and double diaphragm forming, to manufacture low cost fabric preforms suitable for liquid moulding processes. The research has focused on two main aspects: (I) fabric characterisation and modelling and (II) process simulation and optimisation. The forming behaviour of woven fabrics and non-crimp fabrics (NCF) has been investigated to understand the deformation mechanisms and the cause of defects, in order to seek feasible solutions for defect reduction. A non-orthogonal constitutive relation has been developed to capture the nonlinear material behaviour, which was implemented in an explicit finite element model and used to refine the forming process. Results from the material model indicate that pillar stitched NCFs are not as compliant as woven fabrics of the same areal mass. The likelihood of defects is therefore higher for the NCF and the shear behaviour is axisymmetric due to the influence of the stitch yarn. The NCF material exhibits two types of wrinkling during matched tool forming; out-of-plane wrinkling at the ply level (macro-scale wrinkling) induced by excessive shear, and in-plane wrinkling at the bundle level (meso-scale wrinkling) caused by fibre compression. Stitch rupture can also occur at high shear angles, which can lead to further localised wrinkling. Fabric bridging is the dominant defect in large curvature regions when using double diaphragm forming (DDF), and wrinkling was found to be generally lower than in matched-tool forming. The model has been used to successfully identify the cause of all of these defects in NCF preforms manufactured by DDF, and has been used to optimise preform geometry and process parameters to mitigate these problems. Darts were added to preforms to alleviate fabric bridging and improve surface conformity, using the tensile stress in the yarns to identify suitable positions and orientations, minimising the effect on the mechanical performance of the component. An optimisation methodology has been developed for placing local inter-ply stitches on multi-ply preforms, by coupling the FE analysis with a genetic algorithm. The stitches enable multiple plies to be joined together to aid robotic handling and the optimisation routine ensures that the placement of the stitches does not adversely affect the formability of the preform. Results indicate that whilst the inter-ply stitches affect the shear distribution at a global level, the formability of a multi-ply preform can be improved compared to the unstitched counterpart by optimising the pattern of through-thickness stitches. A two-step optimisation method was also developed to optimise the boundary conditions for a matched tool forming scenario. Spring-loaded clamps were used to provide in-plane tension in the fabric plies during forming, rather than using a blank holder to induce tension through friction, providing an opportunity to reduce preform size and therefore waste. The optimisation algorithm was used to determine the location and size of the clamps around the blank perimeter and the stiffness of the attached springs. It was shown that this method can effectively homogenise the global shear angle distribution, reducing the peak shear angle compared to using a segmented blank holder.
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Lind, Markus, e Viktor Sjöblom. "Industrial Sheet Metal Forming Simulation with Elastic Dies". Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-16782.
Testo completoAbstract (sommario):
As part of the development process for new stamping dies, in the automotive sheet metal forming (SMF) industry, the majority of all forming operations are simulated with the Finite Element Method (FEM) before the dies are manufactured. Today, these simulations are conducted with rigid tools under the assumption that there are no tool deformations. However, research shows that tool deformations have an influence on the finished product. In real production these deformations are compensated by manual rework during the try-out. Additional reason for simulating with rigid dies is that there are non-existing simulation methods elaborated for elastic stamping dies. Also, simulation of elastic tools requires high computational power. Since simulations today are performed with rigid stamping dies the purpose of this work is to investigate the conditions of how to conduct SMF-simulations with elastic stamping dies. The object that will be studied is a stamping die for a Volvo XC90 inner door used in a single-action press. This work is part of the development to minimize the manual rework, with the goal to compensate for tool deformations in a virtual environment. Results for rigid stamping dies in LS-Dyna was compared to currently used AutoForm as a pre-study. A simple model was then created to find a suitable method while using elastic stamping dies. The developed method was used for an industrial size stamping die. Since there are little amount of research performed on simulations using elastic stamping dies, elasticity and complexity were gradually introduced into the FE-model. As a first step, only the punch was included as an elastic solid. Secondly, the die was added. Finally, the entire die was simulated as elastic together with the hydraulic cushion of the press. When the FE-model worked as expected a suitable method for minimizing the simulation time with acceptable results was studied. Comparisons of measured- and simulation results show a high correlation. To improve the results from the FE-model factors such as press deformations, advanced friction models, etc. should be included. Conclusions from this work shows that it is possible to perform SMF-simulations with elastic stamping dies. As the computational time normally is high this work also presents a method first step to reduce the computational time with acceptable results. Comparisons between simulations with rigid and elastic stamping dies proves that there are significant differences in the outcome of the two methods.Reduced Lead Time through Advanced Die Structure Analysis - Vinnova
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Siddiqui, Muhammad Ali. "Numerical modelling and simulation of electromagnetic forming process". Strasbourg, 2009. https://publication-theses.unistra.fr/public/theses_doctorat/2009/SIDDIQUI_Muhammad_Ali_2009.pdf.
Testo completoAbstract (sommario):
Le formage électromagnétique est un procédé de mise en forme des métaux à grande vitesse de déformation. Ce procédé permet de déformer des pièces métalliques en déchargeant un courant intense pulsé à travers une bobine se situant à proximité de la pièce. La modélisation numérique des procédés de mise en forme est une approche couramment utilisée pour développer et améliorer (par la réalisation d’études paramétriques) de nouveaux procédés. Le but de cette thèse est de développer un simulateur numérique afin de décrire le procédé de formage électromagnétique et de mieux comprendre les phénomènes physiques intervenant pendant la déformation. Le problème électromagnétique est résolu par la méthode des différences finies afin d’obtenir la pression agissant sur la face de la pièce métallique. Le problème mécanique est quant à lui traité par un code commercial de calcul par éléments finis (ABAQUS/Explicit) en utilisant un algorithme de résolution de type dynamique avec une intégration du temps Explicit. La méthode des différences finies utilisée pour résoudre les équations de Maxwell a été programmée en langage FORTRAN. Ce programme a été validé sur un cas test et comparé aux résultats expérimentaux disponibles dans la littérature et aux prévisions obtenues avec un code libre de calcul par élément finis pour les problèmes de magnétisme (FEMM). Ce programme a été ensuite introduit dans le logiciel ABAQUS via un sous-programme utilisateur VDLOAD. Des simulations d’essais d’expansion de tôles métalliques ainsi que des essais d’expansion et de compression de tubes ont été réalisées. Les prévisions obtenues sont en accord avec les résultats expérimentaux disponibles dans la littératureElectromagnetic sheet forming (EMF) is a high velocity forming process driven by the coupled electromagnetic and mechanical phenomena. The deformation of the workpiece takes place due to the body forces (Lorentz forces) that are created by a pulsed magnetic field produced by a flat spiral coil. Formability can be increased using this high velocity forming technique due to the inertial forces and high strain rates. In this Ph. D. Research, we considered the electromagnetic and the mechanical aspect of the process as two independent problems. We aimed to provide a mathematical model for EMF process, and validate it with existing numerical tools and experiments. We have developed a numerical and analytical tool which can accurately calculate the basic parameters of the EMF process. The finite difference method has been employed to solve the electromagnetic Maxwell’s equations. The pressure acting on the workpiece has been calculated neglecting the influence of the workpiece velocity on the magnetic field. Then it has been treated as a load in the mechanical problem. Numerical simulations of the mechanical problem have been performed with the commercial finite element code ABAQUS/Explicit. The magnetic pressure has been introduced in ABAQUS/Explicit as an analytical pressure distribution with the help of a user-defined sub-routine VDLOAD. FE simulations of the electromagnetic free bulging test have been performed. Furthermore, simulations of tube expansion and compression processes were also undertaken. The FE predictions are globally in agreement with the experimental results available in the literature
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Dogan, Ulug Cagri. "Effect Of Strain History On Simulation Of Crashworthiness Of A Vehicle". Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610725/index.pdf.
Testo completoAbstract (sommario):
In this thesis the sheet metal forming effects such as plastic strain and thickness
changes in the crash have been investigated by numerical analysis.
The sheet metal forming histories of the components of the load path that absorbs the
highest energy during a frontal crash have been considered. To find out the particular
load path, the frontal crash analysis of Ford F250 Pickup has been performed at 56
kph into a rigid wall with finite element analysis without considering the forming
history. The sheet metal forming simulations have been realized for each structural
component building up the particular load path. After forming histories have been
acquired, plastic strain and thickness distributions have been transferred to the frontal
crash analysis. The frontal crash analysis of Ford F250 Pickup has been repeated by
including these to introduce the effect of forming on crash response of the vehicle.
The results of the simulations with and without forming effect have been compared
with the physical crash test results to evaluate the sheet metal forming effect on the
overall crash response. The results showed that with forming history the crash
response of the vehicle and deformations of the particular components have been
changed and the maximum deceleration pulse transferred to the passenger
compartment has decreased. It has seen that a good agreement with physical test
results has been achieved.
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Ledentsov, Dmitry [Verfasser]. "Model adaptivity in sheet metal forming simulation / Dmitry Ledentsov". Aachen : Shaker, 2010. http://d-nb.info/1122546106/34.
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Glavas, Vedran [Verfasser]. "Micromechanical Modeling and Simulation of Forming Processes / Vedran Glavas". Karlsruhe : KIT Scientific Publishing, 2016. http://www.ksp.kit.edu.
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Wang, Tao. "Numerical simulation and optimisation for shot peen forming processes". Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620031.
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Steventon, R. H. "Aspects of numerical simulation of the metal forming process". Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/5467.
Testo completoAbstract (sommario):
Includes bibliographical references.Metal forming is one of the oldest disciplines and dates back many thousands of years. The pressing of metal into shapes as a manufacturing process is widely distributed and is typically performed in engineering workshops. This process can be simulated to a degree, with a computer which provides many economic advantages.
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Lamontagne, Chantal G. Carleton University Dissertation Engineering Mechanical and Aerospace. "Numerical simulation of aluminium sheet forming incorporating plastic anisotropy". Ottawa, 1996.
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Leacock, Alan Gordon. "Numerical simulation of anisotropic plasticity in stretch formed aluminium alloys". Thesis, University of Ulster, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369949.
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Kleditzsch, Stefan. "Beitrag zur Modellierung und Simulation von Zylinderdrückwalzprozessen mit elementaren Methoden". Doctoral thesis, Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-133117.
Testo completoAbstract (sommario):
Drückwalzen als inkrementelles Umformverfahren ist aufgrund seiner Verfahrenscharakteristik mit sehr hohen Rechenzeiten bei der Finite-Elemente-Methode (FEM) verbunden. Die Modelle ModIni und FloSim sind zwei analytisch-elementare Ansätze, um dieser Prämisse entgegenzuwirken. Das für ModIni entwickelte Geometriemodell wird in der vorliegenden Arbeit weiterentwickelt, so dass eine werkstoffunabhängige Berechnung der Staugeometrie ermöglicht wird und ein deutlich größeres Anwendungsspektrum der Methode bereitsteht. Die Simulationsmethode FloSim basiert auf dem oberen Schrankenverfahren und ermöglicht somit eine Berechnung von Zylinderdrückwalzprozessen innerhalb weniger Minuten. Für die Optimierung der Methode FloSim wurden in der vorliegenden Arbeit die analytischen Grundlagen für die Berechnung der Bauteillänge sowie der Umformzonentemperatur während des Prozesses erarbeitet. Weiterhin wurde auf Basis von numerisch realisierten Parameteranalysen ein Ansatz für die analytische Berechnung des Vergleichsumformgrades von Drückwalzprozessen entwickelt. Diese drei Ansätze, zu Bauteillänge, Temperatur und Umformgrad wurden in die Simulationssoftware FloSim integriert und führen zu einer deutlichen Genauigkeitssteigerung der MethodeFlow Forming as incremental forming process is connected with extreme long computation times for Finite-Element-Analyses. ModIni and FloSim are two analytical/elementary models to antagonize this situation. The geometry model, which was developed for ModIni, is improved within the presented work. The improvement enables the material independent computation of the pile-up geometry and permits a wider application scope of ModIni. The simulation method FloSim is based on the upper bound method, which enables the computation of cylindrical Flow Forming processes within minutes. For the optimization of the method FloSim, the basics for the analytical computation of the workpiece length during the process and the computation of the forming zone temperature were developed within this work. Fur-thermore, an analytical approach for the computation of the equivalent plastic strain of cylindrical Flow Forming processes was developed based on numerical parameter analyses. This tree approaches for computing the workpiece length, the temperature and the equivalent plastic strain were integrated in FloSim and lead to an increased accuracy
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Leutz, Daniel Maurice [Verfasser]. "Forming simulation of AFP material layups: Material characterization, simulation and validation / Daniel Maurice Leutz". München : Verlag Dr. Hut, 2016. http://d-nb.info/1115550438/34.
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Goel, Amit. "Blank optimization in sheet metal forming using finite element simulation". Thesis, Texas A&M University, 2004. http://hdl.handle.net/1969.1/3120.
Testo completoAbstract (sommario):
The present study aims to determine the optimum blank shape design for the deep drawing of arbitrary shaped cups with a uniform trimming allowance at the flange i.e. cups without ears. This earing defect is caused by planar anisotropy in the sheet and the friction between the blank and punch/die. In this research, a new method for optimum blank shape design using finite element analysis has been proposed. Explicit non-linear finite element (FE) code LSDYNA is used to simulate the deep drawing process. FE models are constructed incorporating the exact physical conditions of the process such as tooling design like die profile radius, punch corner radius, etc., material used, coefficient of friction, punch speed and blank holder force. The material used for the analysis is mild steel. A quantitative error metric called shape error is defined to measure the amount of earing and to compare the deformed shape and target shape set for each stage of the analysis. This error metric is then used to decide whether the blank needs to be modified or not. The cycle is repeated until the converged results are achieved. This iterative design process leads to optimal blank shape. In order to verify the proposed method, examples of square cup and cylindrical cup have been investigated. In every case converged results are achieved after a few iterations. So through the investigation the proposed systematic method of optimal blank design is found to be very effective in the deep drawing process and can be further applied to other stamping applications.
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Moshfegh, Ramin. "Aspects on finite element simulation of sheet metal forming processes /". Linköping : Department of Solid Mechanics, Department of Mechanical Engineering, Linköping University, 2006. http://www.bibl.liu.se/liupubl/disp/disp2006/tek1042s.pdf.
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Lindbäck, Torbjörn. "Simulation of metal forming processes including impact on product performance /". Luleå, 2003. http://epubl.luth.se/1402-1544/2003/29.
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Arwidson, Claes. "Numerical simulation of sheet metal forming for high strength steels". Licentiate thesis, Luleå, 2005. http://epubl.luth.se/1402-1757/2005/08.
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Lundin, Andreas. "FEM simulation of 3D forming of double curved paper structures". Thesis, KTH, Hållfasthetslära (Inst.), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204951.
Testo completoAbstract (sommario):
This thesis examines the possibility of creating a functional predictive analysis tool that can be utilized to improve testing procedure for new double curved paperboard products. The most common procedure currently is to manufacture several prototype paperboards, perform initial forming tests of the new double curved shape and then iterate until a prototype paperboard successfully forms. A predictive analysis tool could greatly improve the efficiency of the prototype phase by narrowing the initial scope of desired properties. The analysis tool was to be focused on the suitability of the desired shape and the requirements of the material to successfully form. FEM simulations of the forming process were performed and then verified by experiments. It was found that the FEM simulations performed were representative of the experimental results, specifically in regards to plastic strain required and problematic areas relating to fracture. It was also found that the simulation lacked the robustness required for large scale predictive analysis.
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Peter, Simone. "Structure and relaxation of thin glass forming polymer films". Université Louis Pasteur (Strasbourg) (1971-2008), 2007. https://publication-theses.unistra.fr/public/theses_doctorat/2007/PETER_Simone_2007.pdf.
Testo completoAbstract (sommario):
Nous avons utilisé des simulations de dynamique moléculaire pour étudier des films ultra-fins de polymères, à l'aide d'un modèle coarse-grained. Nous avons analysé la dynamique au sein du film, aussi bien en moyenne que par couches en fonction de la distance à la surface. Nous avons déterminé la température de transition vitreuse Tg au cours de refroidissements. Il ressort de ces études que la dynamique est accélérée dans les couches minces par rapport à la situation du fondu en volume, et Tg diminue. Des films de polymères en solution ont également été étudiés en présence d'un solvant explicite. Nous nous sommes intéressés à la formation de films de polymères purs par évaporation du solvant; les résultats obtenus montrent que la dynamique est plus rapide et Tg plus basse en présence du solvant. Alors que nous pouvons observer une diffusion fickienne à des températures supérieures à Tg, pour des températures plus basses, les déviations par rapport à ce comportement sont notables.
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Reddy, Mahender Palvai. "Finite element simulation of three-dimensional casting, extrusion and forming processes". Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-07282008-135311/.
Testo completo
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Diamantopoulou, Evangelia. "Micromorphic Continua : Advanced Multiphysic Modelling and Numerical Simulation of Metal Forming". Thesis, Troyes, 2018. http://www.theses.fr/2018TROY0004.
Testo completoAbstract (sommario):
L'objectif de cette thèse est de démontrer l'efficacité des modèles de comportement élastoplastique fortement couplés à l’endommagement ductile isotrope dans le cadre des milieux micromorphes afin de s’affranchir de la dépendance au maillage lors de la prévision de l’amorçage et de la propagation de la rupture ductile. Cette approche repose sur (i) l’ajout de variables cinématiques micromorphes dans le principe des puissances virtuelles conduisant à de nouvelles équations de bilan ; (ii) l’ajout de nouveaux couples de variables d’état conduisant à de nouvelles équations de comportement ; (iii) une discrétisation spatiale par éléments finis et temporelle par un schéma d’Euler avec un solveur global dynamique explicite et une intégration locale itérative implicite. Les aspects numériques associés sont implémentés dans ABAQUS®/Explicit. Deux éléments bilinéaires quadrangles à "déformation postulée" (2D déformation plane et axisymétrique) ont été développés afin d’introduire les nouvelles formes variationnelles. Les modèles sont validés avec une étude paramétrique pour étudier l'effet de chaque paramètre micromorphe et une méthodologie d'identification de la longueur interne micromorphe liée à l’endommagement micromorphe est proposée. Des essais de traction uniaxiale d’éprouvettes en acier inoxydable 430, des opérations de pliage et de découpage de tôles métalliques en DP1000 et DP600, sont simulées afin de valider la formulation proposée et montrer son efficacité à donner des solutions indépendantes du maillage par rapport au modèle localThe objective of this work is to demonstrate the efficiency of advanced elastoplastic constitutive equations strongly coupled with isotropic ductile damage in the framework of the micromorphic continua in order to overcome the mesh dependency in the prediction of the ductile cracks initiation and propagation. This approach is based on (i) the introduction, in the principle of virtual power, of additional micromorphic kinematic variables leading to additional balance equations; (ii) addition of new micromorphic pairs of state variables leading to additional micromorphic constitutive equations; (iii) spatial discretization by finite elements and time discretization by finite difference scheme with an explicit dynamic global solver and an implicit iterative local integration scheme. The associated numerical aspects are implemented in ABAQUS®/Explicit. Two bilinear quadrilateral assumed strain elements (2D plane strain and axisymmetric) have been developed in order to introduce new weak forms. The models are validated with a parametric study in order to investigate the effect of each micromorphic parameter, and a methodology for the identification of the micromorphic internal length related to the micromorphic damage is proposed. Simple uniaxial tensile tests, sheet bending and blanking processes of metallic components in 430 stainless steel, DP1000 and DP600 dual phase steels respectively are simulated in order to validate the proposed formulation and to show its efficiency in giving mesh independent solutions compared to the purely local models