Die vorliegende Arbeit hat die Entwicklung eines Konzepts für das Materialmodell zur Simulation des Ziehprozesses mit Karton zum Ziel. Der Ziehprozess stellt bei seiner Simulation hohe Anforderungen an das verwendete Materialmodell. Mehrachsige Spannungszustände und die Einflüsse von Temperatur und Feuchtigkeit müssen berücksichtigt werden. Dazu werden Materialverhalten, Materialmodelle und ihre mathematisch-physikalischen Grundlagen, Spannungssituation und Anforderungen des Ziehprozesses an ein Materialmodell analysiert. Es wird ein Konzept dargelegt, in dem die Simulation des Ziehprozesses in drei Schritte unterteilt wird. Im ersten Teil werden Materialfeuchte und Temperatur mit einem zweidimensionalen Netzwerkmodell bestimmt. Im zweiten Schritt werden Materialparameter mit Hilfe eines dreidimensionalen Netzwerkmodells in Abhängigkeit von zuvor ermittelten Feuchte- und Temperaturwerten und mechanischer Belastung gewonnen. Diese Parameter werden im dritten Teil zur Simulation des Ziehprozesses mit einem makromechanischen Materialmodell genutzt. / A concept for the development of a paperboard material model for the simulation of deepdrawing processes is presented in this thesis. Concerning its simulation, the deep drawing process of paperboard is demanding. Complex states of tension, humidity and changes of temperature during the process have to be considered. Thus properties of paperboard, material-models, their mathematical-physical background and tensions during the deep-drawing process are analyzed. A concept for the material-model, dividing the simulation in three steps, is proposed. In the first step, temperature and humidity are determined, using a two-dimensional lattice model. During the second step material parameters, depending on the state of tension are evaluated with a three-dimensional lattice model. The third step contains the simulation of the deep-drawing process with a three-dimensional continuum model.

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.

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In the first part of this thesis, the FE program MSC.Marc is applied for coupled thermomechanical simulations of wire-rod rolling. In order to predict material behaviour of an AISI 302 stainless steel at high strain rates generated during wire-rod rolling, a material model based on dislocation density is applied. Then, the evolution of temperature, strain rate and flow stress is predicted in the first four rolling passes of a wire block. In the second part of the thesis, an alternative approach to simulation of shape rolling is evaluated. The approach is applied in order to save the computational time in cases where many shape-rolling passes are to be simulated. The approach is a combination of the slab method and a 2D FEM with a generalized plane-strain formulation. A number of various isothermal shape-rolling passes are simulated applying the simplified approach. The simulations are carried out using an in-house 2D FE code implemented in Matlab. The results are compared to fully 3D FE analyses. The comparison shows that the simplified approach can predict roll forces and roll torques with a fair accuracy, but the predicted area reductions are a bit underestimated. The reasons for the deviations between the simplified approach and the 3D FEM are discussed. / QC 20101123

No description available.

Realistic assessments of liver injury risk for the entire occupant population require incorporating inter-subject variations into numerical human models. The main objective of this study was to quantify the variations in shape and material properties of the human liver. Statistical shape analysis was applied to analyze the geometrical variation using a surface set of 15 adult human livers recorded in an occupant posture. Principal component analysis was then utilized to obtain the modes of variation, the mean model, and a set of 95% statistical boundary shape models. Specimen-specific finite element (FE) models were employed to quantify material and failure properties of human liver parenchyma. The mean material model parameters were then determined, and a stochastic optimization approach was utilized to determine the standard deviations of the material model parameters. The distributions of the material parameters were used to develop probabilistic FE models of the liver implemented in THUMS human FE model to simulate oblique impact tests under three impact speeds. In addition, the influence of organ preservation on the biomechanical responses of animal livers was investigated using indentation and tensile tests. Results showed that the first five modes of the human liver shape models accounted for more than 70% of the overall anatomical variations. The Ogden material model with two parameters showed a good fit to experimental tensile data before failure. Significant changes of the biomechanical responses of liver parenchyma were found after cooling or freezing storage. The force-deflection responses of THUMS model with probabilistic liver material models were within the test corridors obtained from cadaveric tests. Significant differences were observed in the maximum and minimum principal Green-Lagrangian strain values recorded in the THUMS liver model with the default and updated average material properties. The results from this study could help in the development of more biofidelic human models, which may provide a better understanding of injury mechanisms of the liver during automobile collisions. / Ph. D.

Recent improvements in manufacturing processes and materials properties associated with excellent mechanical characteristics and low weight have became composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite structure failure phenomena are very complex. Several failure criteria and theories have been developed to describe the damage process and how it evolves, but the solution of the problem is still open. Moreover, modern manufacturing processes, e.g. filament winding, have been used to produce a wide variety of structural shapes. Therefore, this work presents the development of a damage model and its application to simulate the progressive failure of flat composite laminates as well as for composite cylinders made by filament winding process. The proposed damage model has been implemented as a UMAT (User Material Subroutine) and VUMAT (User Material Subroutine for explicit simulations), which were linked to ABAQUSTM Finite Element (FE) commercial package. Progressive failure analyses have been carried out using FE Method in order to simulate the failure of filament wound composite structures under different quasi-static and impact loading conditions. In addition, experiments have been performed not only to identify parameters related to the material model but also to evaluate both the potentialities and the limitations of the proposed model. / As recentes melhorias nos processos de fabricação e nas propriedades dos materiais associadas a excelentes características mecânicas e baixo peso tornam os materiais compósitos muito atrativos para aplicação em estruturas aeronáuticas. No entanto, mesmo novos projetos, ainda são muito conservadores, pois os fenômenos de falha dos compósitos são muito complexos. Vários critérios e teorias de falha têm sido desenvolvidos para descrever o processo de dano e sua evolução, mas a solução do problema ainda está em aberto. Além disso, técnicas modernas de fabricação, como o enrolamento filamentar (filament winding) vêm sendo utilizadas para produzir uma ampla variedade de formas estruturais. Assim, este trabalho apresenta o desenvolvimento de um modelo de dano e a sua aplicação para simular a falha progressiva de estruturas planas e cilíndricas fabricadas em material compósito através do processo de filament winding. O modelo de dano proposto foi implementado como sub-rotinas em linguagem FORTRAN (UMAT-User Material Subroutine e, VUMAT-User Material Subroutine para simulações explícitas), que foram compiladas junto ao programa comercial de Elementos Finitos ABAQUSTM. Várias análises numéricas foram realizadas via elementos finitos, a fim de prever a falha dessas estruturas de material compósito sob diferentes condições de carregamentos quase-estáticos e de impacto. Além disso, vários ensaios experimentais foram realizados, a fim de identificar os parâmetros relacionados com o modelo de material, bem como avaliar as potencialidades e as limitações do modelo proposto.

Neste trabalho buscou-se propor e implementar um modelo de material capaz de prever o comportamento mecânico de estruturas em compósitos poliméricos reforçados (CPR). Inicialmente fez-se um levantamento bibliográfico sobre os modos de danificação intralaminar e falhas interlaminares bem como sobre formas de abordagem (analítica e numérica) para tratar esses problemas. Em seguida, foram apresentadas em detalhes as etapas experimentais executadas, descrevendo todo o procedimento de fabricação dos corpos-de-prova e os resultados obtidos a partir dos ensaios quase-estáticos de tração, compressão, cisalhamento e flexão. Com base nesses resultados e em informações provenientes da literatura, propõem-se alguns modelos de material que foram implementados em sub-rotinas FORTRAN. Tais modelos são posteriormente compilados em conjunto com um programa de elementos finitos (ABAQUS®) a fim de serem avaliados e terem seus parâmetros calibrados. Numa primeira fase, através de simulações computacionais dos ensaios de tração e compressão avaliou-se os modelos de material implementados. Numa segunda fase, os parâmetros foram calibrados tomando como base três estudos de caso (flexão, endentação e teste de impacto) envolvendo seqüências de empilhamento distintas. Após a simulação computacional desses estudos, apresentou-se a proposta de uma metodologia para avaliar problemas de impacto a baixa velocidade em estruturas laminadas. Conclui-se assim que o presente projeto de pesquisa traz contribuições inovadoras, mas também apresenta várias perspectivas de trabalhos futuros. / In this work, material models were proposed to predict the mechanical behavior of composite structures. First of all, it was done a study about damage intra-ply and inter-ply (delamination) on composite materials and about analytical and numerical approaches to solve problems of progressive damage on composite structures was performed. After, many specimens were manufactured and experimental tests (tensile, compression, shear and flexural tests) were carried out. Experimental results and information from literature were used to develop some material models, which were implemented using FORTRAN compiler. These material models were compiled with a commercial finite element program (ABAQUS®) in order to evaluate and calibrate parameters of the models. In the first step, computational simulations of tensile and compression test were carried out to evaluate material models implemented. In the second step, the parameters of the material models were calibrated using three case studies (flexural, indentation and impact test) with some staking sequences. After that, a methodology was proposed to evaluate impact problems on composite structures under low velocity. Therefore, this research project not only shows new contributions but also suggests many future investigations.

Recentes melhorias nos processos de fabricação e nas propriedades dos materiais associadas a excelentes características mecânicas e baixo peso tornaram os materiais compósitos muito atrativos para aplicação em estruturas aeronáuticas. No entanto, mesmo novos projetos ainda são muito conservadores, pois os fenômenos de falha dos compósitos são muito complexos. Então, é estratégico entender melhor, bem como prever esses complexos mecanismos de falha, desenvolvendo modelos de materiais mais precisos que venham a diminuir o número de ensaios experimentais, gerando rapidez e economia aos projetos estruturais. Assim, este trabalho apresenta o desenvolvimento de um modelo de material baseado na Mecânica do Dano Contínuo para simular a falha progressiva de estruturas laminadas de carbono/epóxi quando submetidas a carregamentos quase estáticos e de impacto. Várias análises numéricas foram realizadas via elementos finitos, a fim de prever a falha dessas estruturas de material compósito sob essas solicitações. O modelo de dano proposto foi implementado como sub-rotinas em linguagem FORTRAN (UMAT-User Material Subroutine e, VUMAT-User Material Subroutine para simulações explícitas), que foram compiladas junto ao programa comercial de Elementos Finitos ABAQUSTM. Além disso, ensaios experimentais foram realizados, a fim de calibrar parâmetros relacionados ao modelo de material, bem como avaliar as potencialidades e as limitações do modelo de material proposto. / Recent improvements in manufacturing processes and material properties associated to excellent mechanical characteristics and low weight have become composite materials very attractive for application on civil aircraft structures. However, even new designs are still very conservative, because the composite structure failure phenomena are very complex. So, it is strategic to known better and to predict these complex failure mechanisms, developing more accuracy material models, which reduce the number of experimental tests, inducing a fast and economic structural design. Thus, this work show the development of a material model based on Continuum Damage Mechanics to simulate the progressive failure of carbon/epoxy laminate structures under quasi-static and impact loadings. Several numerical analyses were performed via Finite Element Method in order to predict the damage on composite structures under these conditions. The proposed damage model was implemented as a UMAT (User Material Subroutine) and VUMAT (User Material Subroutine for explicit simulations), which were linked to ABAQUSTM. Moreover, experiments were carried out in order to calibrate the material model parameters and to evaluate the potentialities and limitation of the proposed material model, as well.

Este trabalho é uma contribuição à análise progressiva de falhas em materiais compósitos poliméricos. Esses materiais combinam as propriedades de seus constituintes (fibra, resina polimérica e interface) de forma a melhorar o desempenho frente à utilização das fases isoladamente. A combinação de fases permite obter características como baixa densidade e elevada rigidez, que são almejadas pelo segmento aeronáutico, pois podem proporcionar um aumento de autonomia ou da capacidade de carga das aeronaves. A anisotropia inerente aos compósitos torna possível projetá-los de forma a obter-se a rigidez e a resistência desejada. Por outro lado, a anisotropia dificulta a previsão precisa dos mecanismos de falha, e conseqüentemente, do comportamento global da estrutura. Apresenta-se, assim, com base numa revisão bibliográfica criteriosa, bem como, através de resultados experimentais, a avaliação de um modelo de material fenomenológico, onde se identificam modos de falhas intralaminares. Uma vez verificad a falha por algum critério, degradam-se as propriedades do material. O modelo de material foi implementado junto ao pacote de elementos finitos Abaqus através de uma sub-rotina UMAT (\"User Material\"), escrita em Fortran. Em seguida, estudou-se o problema de um laminado em duas configurações de empilhamento (\'[0º] IND.10\' e \'[0º/90º/0º/90º/0º] IND.S\') sob flexão 3-pontos. Os resultados das simulações foram comparados com resultados experimentais, observando erros da ordem de 10%. Sendo que estes foram obtidos em função de um estudo dos parâmetros associados a solução do problema não-linear, tais como: tamanho de incremento de iteração e parâmetros associados à lei de degradação de material. Por fim, concluiu-se que o modelo de material avaliado é adequado para previsão da falha da primeira camada, bem como, da redução da rigidez estrutural e da resistência residual. Sendo que, a resposta teórica obtida se manteve parcialmente dentro dos limites inferior e superior do envelope experimental. / This work is a contribution to the progressive failure analysis in polymer composite materials. These materials combine the properties of its constituents (fiber, resin and interface) in order to improve the performance against the use of phases alone. The combination of the phases can provide characteristics such as low density and high strength, which are desired in the aeronautical segment, because it can increase the autonomy or aircraft payload. The anisotropy inherent in composites turns possible to design the material for a desired stiffness and strength. Furthermore, it turns difficult the prediction of failure mechanisms, and consequently, the overall behavior of the structure. This study presents, based on a review and experimental results, the evaluation of a phenomenological material model, which identify intralaminar failure modes. Once verified the failure by any criterion, the material properties are reduced by a degradation law. The material model was implemented in a UMAT (User Material) subroutine which linked to the finite element package Abaqus. It was applied in the study of 3-point bending problem for two stacking sequences (\'[0º] IND.10\' e \'[0º/90º/0º/90º/0º] IND.S\'). The results were compared with experimental tests, presenting a error in the order of 10%. Since that these where obtained by a study of the parameters associated to the solution of the nonlinear problem, such as: time step, and parameters associated to the material degradation laws. Finally, it was concluded that the material model is judged suitable for predicting the failure of the first ply, the reduction of structural stiffness and the residual strength. Besides, a part of the theoretical response obtained is maintained within the lower and upper limits of the experimental tests envelope.