488 research outputs found
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
Selective laser melting of H13 tool steel powder: effect of process parameter on complex part production
This research work presents the investigation of H13 tool steel powder in the production of parts characterized by complex features via selective laser melting. The authors proposed a benchmark geometry with 40 mm nominal height, self-supported overhanging structure and internal channels. To investigate powder printability and process capabilities, an experimental campaign was designed as a function of laser power, scan speed and hatching distance. Full dense parts exhibiting 99.92% internal density have been achieved by imposing a laser power equal to 150 W, a scan speed equal to 500 mm/s and a hatching distance equal to 120 µm, while high geometrical accuracy in terms of no material drops along sample edges and low-dimensional deviations of the realized sloping surfaces (i.e., + 0.23° and − 0.90° for nominal 35° and 40° overhang, respectively) has been achieved for 150 W, 1000 mm/s, and 100 µm. Findings open the way to use SLM technology in the design of advanced cutting tool solutions
From 3D Models to 3D Prints: an Overview of the Processing Pipeline
Due to the wide diffusion of 3D printing technologies, geometric algorithms
for Additive Manufacturing are being invented at an impressive speed. Each
single step, in particular along the Process Planning pipeline, can now count
on dozens of methods that prepare the 3D model for fabrication, while analysing
and optimizing geometry and machine instructions for various objectives. This
report provides a classification of this huge state of the art, and elicits the
relation between each single algorithm and a list of desirable objectives
during Process Planning. The objectives themselves are listed and discussed,
along with possible needs for tradeoffs. Additive Manufacturing technologies
are broadly categorized to explicitly relate classes of devices and supported
features. Finally, this report offers an analysis of the state of the art while
discussing open and challenging problems from both an academic and an
industrial perspective.Comment: European Union (EU); Horizon 2020; H2020-FoF-2015; RIA - Research and
Innovation action; Grant agreement N. 68044
A new overhang constraint for topology optimization of self-supporting structures in additive manufacturing
This work falls within the scope of computer-aided optimal design, and aims to integrate the topology optimization procedures and recent additive manufacturing technologies (AM). The elimination of scaffold supports at the topology optimization stage has been recognized and pursued by many authors recently. The present paper focuses on implementing a novel and specific overhang constraint that is introduced inside the topology optimization problem formulation along with the regular volume constraint. The proposed procedure joins the design and manufacturing processes into a integrated workflow where any component can directly be manufactured with no requirement of any sacrificial support material right after the topology optimization process. The overhang constraint presented in this work is defined by the maximum allowable inclination angle, where the inclination of any member is computed by the Smallest Univalue Segment Assimilating Nucleus (SUSAN), an edge detection algorithm developed in the field of image analysis and processing. Numerical results on some benchmark examples, along with the numerical performances of the proposed method, are introduced to demonstrate the capacities of the presented approach.This work was supported by The European Regional Development Fund (ERDF-FEDER) and the Ministry of Education and Science in Spain through the DPI2015-64863-R project (MINECO/FEDER-UE). The authors also wish to thank the Basque Government for financial assistance through IT919-16
Study of lightweighting structural design considering 3D printing constraints
One of the current challenges of the aerospace industry is the exploration of new lightweighting structures to reduce fuel consumption and limiting the environmental impact. The use of numerical methods concerning topology optimization techniques allows the obtaining of such weight reduction, also minimizing both design time and costs, and hence accelerating the design process. Nevertheless, current structural optimization leads to the apparition of complex shapes and volumes with unintuitive holes, thus needing the use of additive manufacturing constraints - minimum length scales and overhanging - to ensure manufacturability. Considering the background exposed above, the aim of this project is to study the feasibility of heuristic designs concerning lightweighting structures, materialized with additive manufacturing and considering 3D printing constraints. The design stage will be developed by means of topology optimization techniques, applied to anisotropic filtering. The methodology employed has considered all details concerning Computational Solid Mechanics (CSM) techniques used in structures optimization, as well as additive manufacturing techniques, different case studies definition and their feasibility study. More specifically, in the context of CSM, the use of Finite Element Methods (FEM) in the classical elastic problem is reviewed, as well as current topology optimization techniques, so as to implement FEM in optimization algorithms. Thus, theoretical basis in additive manufacturing techniques are reviewed, along with the mathematical formulation of length scale and overhang constraints. Lastly, the programming stage is performed by previously defining the working environment, consisting in the use of Object-Oriented Programming within the git Version Control System, and hence establishing the computational domain definition for all cases, the meshing process and the simulation setup. In the end, the present project has accomplished the main objectives, giving a positive answer to the creation of lightweighting structures and fulfillment of 3D printing constraints. Indeed, FEM combined with topology optimization techniques has led to the obtaining of optimized designs, fulfilling an objective function and a set of constraints, considering both design variables approaches, density and level set. Besides, an additional shape functional has been defined as a penalty contribution to the main cost function in order to fulfill 3D printing constraints - the anisotropic perimeter - being the evolution of the standard isotropic one, both applied to total and relative perimeters. This shape functional self-penalizes length scale constraints and keeps control in overhanging phenomena by orienting the topologies with the definition of a virtual anisotropic stiffness matrix. Results obtained show that the apparition of local features with small length scales has been avoided when including either isotropic or anisotropic perimeter as a penalty term. Furthermore, vertical tendency orientation of topologies has been generally obtained with the anisotropic cases, along with penalization of horizontal features. Overall, this project has become clearly relevant for the exploration of new lightweighting structures, achieving weight reduction with topology optimization techniques. Further exploration remains in the course of PhD professionalization, specially when considering phase-field models, high-performance computing and large-scale optimization inside the non-linear regime
Optimal Design of Wire-and-Arc Additively Manufactured I-Beams for Prescribed Deflection
Alloys fabricated by wire-and-arc additive manufacturing (WAAM) exhibit a peculiar anisotropy in their elastic response. As shown by recent numerical investigations concerning the optimal design of WAAM-produced structural components, the printing direction remarkably affects the stiffness of the optimal layouts, as well as their shape. So far, single-plate specimens have been investigated. In this contribution, the optimal design of WAAM-produced I-beams is addressed assuming that a web plate and two flat flanges are printed and subsequently welded to assemble the structural component. A formulation of displacement-constrained topology optimization is implemented to design minimum weight specimens resorting to a simplified two-dimensional model of the I-beam. Comparisons are provided addressing solutions achieved by performing topology optimization with (i) conventional isotropic stainless steel and with (ii) WAAM-produced orthotropic stainless steel at prescribed printing orientations. Lightweight solutions arise whose specific shape depends on the selected material and the adopted printing direction
Flexural bending test of topology optimization additively manufactured parts
The aim of this work is to model, manufacture, and test an optimized Messerschmitt-BölkowBlohm beam using additive manufacturing. The implemented method is the Solid Isotropic Material with Penalization of a minimum compliance design. The Taubin smoothing technique was used to attenuate geometric noise and minimize the formation of overhanging angles and residual stresses due to the thermal activity of the selective laser melting process. The optimized model required examination and repair of local errors such as surface gaps, non-manifold vertices, and intersecting facets. A comparison between experimental and numerical results of the linear elastic regimes showed that the additively manufactured structure was less stiff than predicted. Potential contributors are discussed, including the formation of an anisotropic microstructure throughout the layer-by-layer melting process. In addition, the effect of selective laser melting process on the mechanical properties of stainless steel 316l-0407 and its influence on structural performance was described
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