Spectral Modeling and Virtual Restoration on a Polychrome Medieval Sculpture

The presented work is led in the framework of a general collaboration between three academic labs, industrial partners and Cultural institutions (Centre des Monuments Nationaux, Louvre museum). Such a pluridisciplinary work always in progress at Ecole Centrale Paris deals with 3D digitization, simulation, rapid prototyping, virtual restoration applied on a french medieval sculpture. The main purpose is to virtually represent a polychrome statue of the XIIIth century in high quality spectral rendering, to simulate its visual and original appearance at that period. The complete process used throughout all the phases of the project mainly involves optical devices that ensure no physical contact with the museum object. This article describes the complete chain of engineering resources and the main models we used for accomplishing our objective. From 3D capture without contact to plaster replica, the complete process will be described and illustrated with images and objects during the conference. Some sequences extracted from the didactic and scientific movies produced will also be presented

Open-Source TIG-Based Metal 3D-Printing

Metal 3-D printing has been relegated to high-cost proprietary high-resolution systems and low-resolution low-cost metal inert gas (MIG) systems. In order to provide a path to high-resolution, low-cost, metal 3-D printing, this manuscript proposes a new open source metal 3-D printer design based around a low-cost tungsten inert gas (TIG) welder coupled to a commercial open source self replicating rapid prototyper. Optimal printing parameters for the machine are acquired using a novel computational intelligence software. TIG has many advantages over MIG, such as having a low heat input, clean beads, and the potential for both high-resolution prints as well as insitu alloying of complex geometries. The design can be adapted to most RepRap-class systems and has a basic yet powerful free and open source software (FOSS) package for the characterization of the 3-D printer. This system can be used for fabricating custom metal scientific components and tools, near net-shape structural metal component rapid prototyping, adapting and depositing on existing metal structures, and is deployable for in-field prototyping for appropriate technology applications

Porosity in Aluminum Alloys:Visualization, Characterization, and Modeling

Porosity is one of the major defects in castings because it reduces the mechanical properties of a cast piece [1]. Porosity formation results from the effect of two concomitant mechanisms, namely solidification shrinkage and segregation/precipitation of gases [1]. A model for the prediction of microporosity, macroporosity and pipe shrinkage during the solidification of alloys has been developed at the Computational Materials Laboratory (LSMX-EPFL) [2]. This model has then been improved by taking into account the effect of various alloying elements and gases on porosity formation [3, 4, 5]. However, the modeling of two physical phenomena still needed to be improved: (i) the curvature influence and (ii) the hydrogen diffusion influence on the growth of pores. The effect of pinching, i.e. the pores are forced by the growing solid network to adopt a complex non spherical shape, induces curvature restriction to the pores. This pinching effect can be a limiting factor for the growth of pores and is too simply modeled in the model of Péquet et al. [2]. Several other pinching models exist, but a rigorous experimental study to validate either one of these models is needed. Additionally, Carlson et al. [6] have recently shown that hydrogen diffusion might also be a limiting factor for the growth of pores. In the model of Péquet et al. [2], this effect was not taken into account. This thesis is mainly aimed to (i) provide experimental results that specifically validate the pinching model developed by Couturier et al. [4], (ii) investigate the influence of hydrogen diffusion on the growth of pores and (iii) provide a new model that takes into account the pinching effect and the hydrogen diffusion influence on the growth of pores. At first, pores formed in aluminum-copper (Al-Cu) samples (cast under controlled conditions) have been analyzed using high resolution X-ray tomography. The influence of the alloy inoculant, copper content, cooling rate and initial hydrogen content on the morphology of pores has been investigated. The results show that the curvature of micropores pinched in either non-inoculated or inoculated Al-4.5wt%Cu alloys can be fairly well approximated to that of cylinders. The results also show that the pinching model must be function of (i) the volume fraction of the primary phase gα and (ii) the secondary dendrite arm spacing λ2. However, the influence of the initial hydrogen content appears to be negligible. The pinching model developed by Couturier et al. [4] accounts for these observations and their relation fits fairly well the average mean curvature value of our experimental data. A new model has been developed to calculate an effective hydrogen diffusion coefficient De(gs), that is a function of the volume fraction of solid only. For that purpose, in-situ X-ray tomography has been performed on Al-Cu alloys. For each volume fraction of solid 0.6 ≤ gs ≤ 0.9, a representative volume element of the microstructure has been obtained from the tomography data. Solid and liquid voxels being assimilated to solid and liquid nodes respectively, a hydrogen diffusion equation has then been solved numerically. Calculations have been run until steady-state was reached in order to deduce De(gs) and the simulation results were successfully compared with a new theory based on effective-medium approximations. Both approaches lead to the main conclusion that hydrogen diffusion through the solid phase cannot be neglected, unlike it is assumed in the model of Carlson et al. [6]. Next, using the pinching model of Couturier et al. [4] and the obtained De(gs), a new volume-averaged model has been developed in order to simulate the growth of pores limited by (i) the curvature of the pore phase and (ii) the diffusion of hydrogen. The results show that, although hydrogen diffusion can be a limiting factor for the growth of pores, the pinching effect has a much larger influence. Accordingly, any model for porosity prediction should carefully take into account the influence of curvature and hydrogen diffusion on the growth of pores. In order to ripen this study at a refined scale, a 2D phase-field model has been developed to describe the complex shape of a pore formed within interdendritic liquid channels [7]. The influence of the solid, which can force the pore to adopt a non-spherical shape, is taken into account through the geometry of the domain and appropriate boundary conditions. This model accounts for curvature influence and hydrogen diffusion in the liquid, two of the main aspects governing the growth kinetics of a pore. However, the model still needs to be combined with a description of the liquid flow induced by the pore growth. Basically, this model should serve as a sound basis for further developments that might lead to more sophisticated pinching models. Finally, an experimental study has been conducted in order to track the inoculant influence on the shape of pipe shrinkage. Simultaneously, pipe shrinkage calculations (using the model of Péquet et al. [2]) were performed in order to track the influence of the gs,c parameter on the shape of the pipe shrinkage. This gs,c parameter corresponds to the critical volume fraction of solid at which mass feeding stops. Comparisons between experimental and simulation results show that the gs,c parameter should be set equal to 0.6 or 0.1 for a casting simulation of an inoculated or non-inoculated alloy, respectively

Additive Manufacturing Technologies and Applications

The present Special Issue proposes articles in the area of Additive Manufacturing with particular attention to the different employed technologies and the several possible applications. The main investigated technologies are the Selective Laser Sintering (SLS) and the Fused Deposition Modelling (FDM). These methodologies, combined with the Computer Aided Design (CAD), provide important advantages. Numerical, analytical and experimental knowledge and models are proposed to exploit the potential advantages given by 3D printing for the production of modern systems and structures in aerospace, mechanical, civil and biomedical engineering fields. The 11 selected papers propose different additive manufacturing methodologies and related applications and studies

The 2019 materials by design roadmap

Advances in renewable and sustainable energy technologies critically depend on our ability to design and realize materials with optimal properties. Materials discovery and design efforts ideally involve close coupling between materials prediction, synthesis and characterization. The increased use of computational tools, the generation of materials databases, and advances in experimental methods have substantially accelerated these activities. It is therefore an opportune time to consider future prospects for materials by design approaches. The purpose of this Roadmap is to present an overview of the current state of computational materials prediction, synthesis and characterization approaches, materials design needs for various technologies, and future challenges and opportunities that must be addressed. The various perspectives cover topics on computational techniques, validation, materials databases, materials informatics, high-throughput combinatorial methods, advanced characterization approaches, and materials design issues in thermoelectrics, photovoltaics, solid state lighting, catalysts, batteries, metal alloys, complex oxides and transparent conducting materials. It is our hope that this Roadmap will guide researchers and funding agencies in identifying new prospects for materials design

Apocalypse and recuperation: Blake and the maw of commerce

The paper is a "materialist" reading of Blake's illuminated works. It examines the copperplate method itself as the main theme of Blake's work, and also as a potentially practical means of conveying Blake's art to its intended audience. The question of audience must be at the center of any avowedly prophetic project. Did Blakean production actually facilitate reception? Are we the audience it sought? What forms of supplementary reproduction are necessary for modern discourse on Blake, and what are the effects of such mediation? To what extent does reproduction undermine. sublate, cancel or recuperate Blakean priorities even as it seeks to represent them? What do we actually read when we read a reproduction? The paper also thinks through the Blakean problem to a broader consideration of artistic projects operating marginally to the predominant cultural economy. and of their relation to criticism

Predicting the reflectivity and colour of metals from first principles

Gold and copper are the only two elemental metals that show a characteristic colour, due to the presence of a drop in the reflectivity curve inside the visible range. Reflectivities of all other metals are in general high and flat for all visible frequencies, making they appear shiny and silvery white. Nowadays, with state-of-the-art theoretical methods, it is possible to calculate reflectivity and colour of a material by means of first-principles simulations and, as a consequence, predict the colour of new metal alloys. The computational approach for material design can be, for example, useful for applications related to jewellery and the high-end watch industry, where there is the demand, due to market and fashion trends, for precious-metal alloys with specific optical properties. The simulations can therefore substitute or, at least, reduce the use of expensive and inefficient trial-and-error experiments, which is otherwise the common route followed by researchers and manufacturers in order to identify novel materials. Because of its unique properties (i.e. characteristic red-yellow colour, high corrosion resistance, high density and considerable malleability), since ancient times gold and, as a consequence, its alloys have been of particular interest for jewellery applications. In particular, gold alloys and intermetallics show a broad spectrum of colours (yellow, red, purple, white and others), which can be tuned by varying the alloying elements in the material. In this thesis, we first discuss the physical approach used to simulate the optical properties of metals, that is the independent particle approximation for the evaluation of the dielectric function, based on the calculation of both interband and intraband contributions from the electronic structure obtained with density-functional theory simulations. We also describe in some detail the computational approach developed to perform in practice first-principles simulations in both an efficient and automatic way. For this purpose, on one hand we have developed a code, named SIMPLE, to calculate optical properties using Shirley's interpolation method, which is an efficient and robust automatic procedure. On the other hand, in order to have reliable band structures as the starting ingredients for the evaluation of the dielectric function, we have exploited the results of a protocol, named SSSP, developed by us to test the precision and performance of pseudopotentials for all elements. Using the results above, we then show through a systematic study on elemental metals and extensive comparisons with experimental data that the chosen computational approach is able to reproduce the correct behaviour of the reflectivity curve and to capture the main differences in optical properties among several elements of the periodic table. Finally, we perform a similar study on metal alloys by considering different types of compounds, i.e. ordered intermetallics, disordered solid solutions and heterogeneous alloys. In particular, we show through a comparison with several experimental results that, if the appropriate methods are used for the simulation of the different types of compounds, (i) the simulated colours of known coloured intermetallics are often in quantitative agreement with experiments, (ii) the main mechanisms that modify the colour of bulk gold in alloys are qualitatively captured and that (iii) we manage to reproduce the main colour trends in noble-metal-based binary alloys

Vermessung, Modellierung und Verifizierung von Licht-Masse-Interaktions-Phänomenen

The photo-realistic rendering of scenes showing natural phenomena requires skilled graphic designers not only to produce a convincingly good-looking image but also to convey physical plausibility. This is especially important in industrial context, where a modelled scene showcasing a product has to approximate the actual environment of a product as closely as possible, e.g. in automotive industries. In this thesis, new techniques to measure natural phenomena are presented in order to provide new or verify existing models for rendering the physically plausible image. In contrast to other approaches, the measurement is performed using nonconventional methods: an ellipsometer is employed to capture the specular reflectance with respect to the polarisation behaviour, a transmissive screen attached to a glass tank is imaged to capture underwater reflectances, and the Microsoft Kinect, a motion capturing device, is used to detect the gas flows around objects. The results are the verification of existing, physically plausible models for commodity metals, an enhanced reflectance model for materials immersed in transparent media with known refractive index, and the reconstruction of two-phase gas flows around occluding objects.Das Erzeugen von Szenen mit natürlichen Phänomenen in fotorealistischer Qualität ist aufwändig, weil nicht nur ein realistisches Bild erstellt werden soll, sondern auch physikalische Plausibilität in Bezug auf das modellierte Phänomen verlangt wird. Besonders in der Industrie, z.B. in der Automobilindustrie, sollte die modellierte Szene, in der ein Produkt eingesetzt wird, der tatsächlichen Einsatzumgebung so naturgetreu wie möglich ähneln. In dieser Dissertation werden neue Ansätze zum Messen von natürlichen Phänomenen präsentiert, die es ermöglichen, für bestimmte Phänomene neue Modelle zu erstellen oder bestehende Modelle erschöpfender zu verifizieren, um damit physikalische Plausibilität für Szenen, die am Computer ereugt werden, zu gewährleisten. Im Unterschied zu anderen Verfahren, werden unkonventionelle Methoden zur Messung umgesetzt: Mit Hilfe eines Ellipsometers wird die Oberflächenreflektanz von Metallen so vermessen, dass auch Änderungen im Polarisationszustand des Lichtes erfasst werden. Unterwasserreflektanzen von Materialien werden mit Hilfe eines lichtdurchlässigen Diffusers abgebildet, der an einen Glasbecher angebracht wird, und der Bewegungssensor Kinect von Microsoft wird verwendet, um Gasströmungen um Objekte zu detektieren. Die Ergebnisse sind die Verifikation von bestehenden Modellen für handelsübliche Metallflächen, ein erweitertes Reflektanzmodell für Oberflächen, die in refraktive Medien eingetaucht werden und die Rekonstruktion von Gasströmungen um Objekte

Materials & Machines: Simplifying the Mosaic of Modern Manufacturing

Manufacturing in modern society has taken on a different role than in previous generations. Today’s manufacturing processes involve many different physical phenomenon working in concert to produce the best possible material properties. It is the role of the materials engineer to evaluate, develop, and optimize applications for the successful commercialization of any potential materials. Laser-assisted cold spray (LACS) is a solid state manufacturing process relying on the impact of supersonic particles onto a laser heated surface to create coatings and near net structures. A process such as this that involves thermodynamics, fluid dynamics, heat transfer, diffusion, localized melting, deformation, and recrystallization is the perfect target for developing a data science framework for enabling rapid application development with the purpose of commercializing such a complex technology in a much shorter timescale than was previously possible. A general framework for such an approach will be discussed, followed by the execution of the framework for LACS. Results from the development of such a materials engineering model will be discussed as they relate to the methods used, the effectiveness of the final fitted model, and the application of such a model to solving modern materials engineering challenges