Numerical Modelling and Simulation of Metal Processing

This book deals with metal processing and its numerical modelling and simulation. In total, 21 papers from different distinguished authors have been compiled in this area. Various processes are addressed, including solidification, TIG welding, additive manufacturing, hot and cold rolling, deep drawing, pipe deformation, and galvanizing. Material models are developed at different length scales from atomistic simulation to finite element analysis in order to describe the evolution and behavior of materials during thermal and thermomechanical treatment. Materials under consideration are carbon, Q&T, DP, and stainless steels; ductile iron; and aluminum, nickel-based, and titanium alloys. The developed models and simulations shall help to predict structure evolution, damage, and service behavior of advanced materials

Computational Methods for Failure Analysis and Life Prediction

This conference publication contains the presentations and discussions from the joint UVA/NASA Workshop on Computational Methods for Failure Analysis and Life Prediction held at NASA Langley Research Center 14-15 Oct. 1992. The presentations focused on damage failure and life predictions of polymer-matrix composite structures. They covered some of the research activities at NASA Langley, NASA Lewis, Southwest Research Institute, industry, and universities. Both airframes and propulsion systems were considered

TMC Behavior Modeling and Life Prediction Under Multiaxial Stresses

The goal of this program was to manufacture and burst test small diameter SCS-6/Ti-6Al-4V composite rings for use in the design of an advanced titanium matrix composite (TMC) impeller. The Textron Specialty Metals grooved foil-fiber process was successfully used to make high quality TMC rings. A novel spin test arbor with "soft touch" fingers to retain the TMC ring was designed and manufactured. The design of the arbor took into account its use for cyclic experiments as well as ring burst tests. Spin testing of the instrumented ring was performed at ambient, 149C (300F), and 316C (600F) temperatures. Assembly vibration was encountered during spin testing but this was overcome through simple modification of the arbor. A spin-to-burst test was successfully completed at 316C (600F). The rotational speed of the TMC ring at burst was close to that predicted. In addition to the spin test program, a number of SCS-6/Ti-6Al-4V test panels were made. Neat Ti-6Al-4V panels also were made

Review of the Synergies Between Computational Modeling and Experimental Characterization of Materials Across Length Scales

With the increasing interplay between experimental and computational approaches at multiple length scales, new research directions are emerging in materials science and computational mechanics. Such cooperative interactions find many applications in the development, characterization and design of complex material systems. This manuscript provides a broad and comprehensive overview of recent trends where predictive modeling capabilities are developed in conjunction with experiments and advanced characterization to gain a greater insight into structure-properties relationships and study various physical phenomena and mechanisms. The focus of this review is on the intersections of multiscale materials experiments and modeling relevant to the materials mechanics community. After a general discussion on the perspective from various communities, the article focuses on the latest experimental and theoretical opportunities. Emphasis is given to the role of experiments in multiscale models, including insights into how computations can be used as discovery tools for materials engineering, rather than to "simply" support experimental work. This is illustrated by examples from several application areas on structural materials. This manuscript ends with a discussion on some problems and open scientific questions that are being explored in order to advance this relatively new field of research.Comment: 25 pages, 11 figures, review article accepted for publication in J. Mater. Sc

A novel approach towards a lubricant-free deep drawing process via macro-structured tools

In today’s industry, the sustainable use of raw materials and the development of new green technology in mass production, with the aim of saving resources, energy and production costs, is a significant challenge. Deep drawing as a widely used industrial sheet metal forming process for the production of automotive parts belongs to one of the most energy-efficient production techniques. However, one disadvantage of deep drawing regarding the realisation of green technology is the use of lubricants in this process. Therefore, a novel approach for modifying the conventional deep drawing process to achieve a lubricant-free deep drawing process is introduced within this thesis. In order to decrease the amount of frictional force for a given friction coefficient, the integral of the contact pressure over the contact area has to be reduced. To achieve that, the flange area of the tool is macro-structured, which has only line contacts. To avoid the wrinkling, the geometrical moment of inertia of the sheet should be increased by the alternating bending mechanism of the material in the flange area through immersing the blankholder slightly into the drawing die

Machining strategies for distortion control during high speed machining

Airframe structural components that are machined from aluminium forgings or plate stock represent a significant contribution to the cost of both military and commercial aircraft. These components tend to distort due to heat treating induced bulk stresses and machining. Correcting these distortions increase costs and manufacturing lead times, especially for a high-volume, high-quality production company. In addition to this, variation in the residual stress profile from component to component is common due to variation in the condition of supply state. There is therefore a need to understand and model the effects of heat-treating and machining strategies on distortion and to predict, minimize, and control these distortions. This thesis addresses the modeling, data acquisition, and validation of residual stress and distortion models using different aluminium test cases. The project is divided into different technical studies to build the modelling capability: In the first study, aluminium 7050 material data and heat transfer coefficients were experimentally acquired. This data was to be used as an input to demonstrate the capability of Finite Element (FE) modelling as the main tool to predict and design robust strategies in the presence of residual stress variation due to processing or geometric differences. In the second study, the simulation study was performed to improve the machining distortion by using finite element (FE) modelling on varying residual stress profiles of aluminium coupons. Other studies included the influence of tool paths, the pocketing sequence, billet orientation and part location on machining distortion. Finally, utilizing the knowledge acquired, a machining process strategy for distortion control was proposed

Metodologias para projeto mecânico ótimo de estruturas espaciais obtidas por fabrico aditivo

Additive Layer Manufacturing (ALM) is growing rapidly due to the unprecedented design freedom. Thus, the structures' complexity can be drastically increased without significant raises in costs. However, the economic viability of ALM is strongly dependent on the full exploration of the referred design freedom. In fact, the ALM is only cost-effective in highly customized parts. Moreover, the mechanical behavior of materials processed via ALM is an ongoing challenge due to defects, uncertainties in material characterization, and verification methods. Thus, the goal of the present work is the development of a robust methodology for the mechanical optimum design of metallic space structures obtained from additive manufacturing. Thus, two main tasks were established. The first task is related to the mechanical characterization of a Ti6Al4V alloy, processed via Selective Laser Melting (SLM). Therefore, an experimental testing campaign of Ti6Al4V samples is presented using homogeneous macroscopic testing (tensile, compression, density, hardness, and fatigue) and microscopic testing (defects detection via microcomputed tomography). These samples show better static properties than the other counterparts, obtained by traditional manufacturing processes. However, the repeatability of the SLM samples is still a challenge (particularly in its fatigue behavior) and more testing is needed. Furthermore, these campaigns are expensive and, consequently, more information per test is required. With the development of full-field measurement methods, material model calibration strategies call upon the use of heterogeneous testing specimens. In the scope of this work, an indirect TO methodology is presented, being capable of designing a wide range of different heterogeneous specimens. Then, a stress states performance indicator is also presented to help the selection of the most promising geometry. The second task is related to the definition of the engineering cycle for ALM structures in its mains phases: (i) design for ALM, (ii) bridging between Topology Optimization (TO) and ALM, (iii) process simulation and structural verification, and (iv) manufacturing. Concerning the first phase, ALM provides great geometric freedom however, there are some design limitations. Therefore, a systematic design methodology is presented, being based on a topology optimization algorithm capable of incorporating the main ALM design limitations (minimum member size and overhang angle). Furthermore, the non-trivial task of bridging between TO and the final smooth geometry is also studied (second phase). The referred task uses a Laplacian smoothing algorithm, which is based on the new concept of mutable diffusion. This new concept shows better properties than the classic algorithms, giving promising results. Furthermore, a new volume constraint is presented, which exhibits a less detrimental impact on the chosen structural indicators. Regarding the remaining phases, these were analyzed via industrial case studies. For instance, process simulation can provide crucial insight into the optimum manufacturing direction and might dictate the difference between success and failure upon manufacturing. The impact of this Ph.D. is related with some improvements in (i) the characterization of ALM-produced materials as well as the geometry of the specimens used for their characterization; and in (ii) the engineering cycle of ALM structures, allowing higher efficiency in the structural solutions for the space industry with lower costs.O uso do fabrico aditivo por camadas está a crescer a um elevado ritmo devido À elevada liberdade de projeto de estruturas. Assim, a complexidade das estruturas pode ser aumentada significativamente sem incrementos significativos nos custos. Todavia, a viabilidade económica do fabrico aditivo por camadas é fortemente dependente de uma exploração inteligente da liberdade de projeto estrutural. Na verdade, o fabrico aditivo por camadas só é rentável em peças de elevada complexidade e valor acrescentado. Adicionalmente, o comportamento mecânico de materiais processados através do fabrico aditivo por camadas é ainda um desafio por resolver devido à existência de defeitos, incertezas na caracterização de materiais e nos seus métodos de velicação. Deste modo, o objetivo deste trabalho é o desenvolvimento de uma metodologia robusta que permita o projeto mecânico ótimo de estruturas obtidas por fabrico aditivo para a indústria espacial. Para isso, foram estabelecidas duas tarefas principais. A primeira tarefa está relacionada com a caracterização mecânica da liga Ti6Al4V, processada através da fusão seletiva a laser. Portanto, foi realizado uma campanha de testes experimentais com provetes da liga Ti6Al4V composta por testes macroscópicos homogéneos (tração, compressão, densidade, dureza e fadiga) e testes microscópicos (deteção de defeitos usando uma análise com recurso à tomografia microcomputorizada). Foi verificado que estas amostras exibem melhor propriedades estáticas que amostras idênticas produzidas através de processos tradicionais. Contudo, a sua repetibilidade ainda é um desafio (particularmente o comportamento à fadiga), sendo necessário mais testes. Adicionalmente, estas campanhas experimentais são onerosas e, consequentemente, é crítico obter mais informação por cada teste realizado. Dado o desenvolvimento dos métodos de medição full-field, as estratégias de calibração de modelos de material propiciam o uso de provetes heterogéneos em testes mecânicos. No ^âmbito deste trabalho apresenta-se uma metodologia de otimização topológica indireta capaz de projetar uma grande variedade de provetes heterógenos. Posteriormente apresenta-se um indicador de desempenho baseado na quantidade de estados de tensão para selecionar o provete mais promissor. A segunda tarefa está relacionada com a definição do ciclo de engenharia para o fabrico aditivo por camadas de estruturas metálicas nas suas fases principais: (i) projeto para fabrico aditivo por camadas, (ii) transição entre a otimização topológica e o fabrico aditivo por camadas, (iii) simulação do seu processo de fabrico e sua verificação estrutural e (iv) fabrico. Relativamente à primeira fase, o fabrico aditivo por camadas proporciona uma grande liberdade geométrica, contudo existe limitações ao design. Portanto é apresentada uma metodologia de projeto sistemática, baseada num algoritmo de otimização topológica capaz de incorporar as principais limitações de projeto do fabrico aditivo por camadas tais como a espessura mínima e ângulo do material sem suporte. Adicionalmente, a tarefa complexa de efetuar a transição entre os resultados da otimização topológica e uma geometria final suave também é objeto de estudo. A tarefa anteriormente referida baseia-se na suavização Laplaciana que por sua vez se baseia no novo conceito de difusão mutável. Este novo conceito apresenta melhores e mais promissores resultados que os algoritmos clássicos. Adicionalmente, é apresentado uma nova restrição de volume que proporciona um menor impacto nos indicadores estruturais escolhidos. Relativamente às restantes fases, estas são analisadas através de casos de estudo industriais. A título exemplar, a simulação do processo de fabrico pode fornecer informações crucias para a escolha da direção de fabrico que, por sua vez, pode ditar a diferença entre o sucesso ou o insucesso durante o fabrico. O impacto deste trabalho está relacionado com melhorias na (i) caracterização de materiais produzidos através de fabrico aditivo por camadas assim como nas geometrias de provetes usados durante a sua caracterização e no (ii) ciclo de projeto em engenharia de estruturas obtidas através do fabrico aditivo por camadas, permitindo soluções estruturais com maior eficiência e menor custo para indústria espacial.Programa Doutoral em Engenharia Mecânic