Publications

2018

Shapes & DOF: on the use of modal concepts in the context of parametric non-linear studies

Auteurs : BALMES, Etienne
Publisher :
Physical responses tend to lie within restricted subspaces even for parametric problems. For a given subspace, the choice of a basis defines Degree Of Freedom (DOF) and this choice may give interesting meaning to the associated amplitudes. Classical modal analysis builds subspaces combining modeshapes and static responses. Parametric loads for non-linear, damped, variable, ... structures are discussed to extend the theory and illustrated for test and simulation cases. Challenges in shape extraction and basis generation techniques are then detailed. Introducing the ability to manipulate models with variable junction properties, component material and geometry, load and operating conditions, ... opens new questions on the quantification and tracking of changes and objectives throughout design exploration. The definition of a reference linear system and the use of global and/or local modal DOF are shown to provide an interesting perspective.
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2018

Reduced physical aging rates of polylactide in polystyrene/polylactide multilayer films from fast scanning calorimetry

Auteurs : MONNIER, Xavier FERNANDES NASSAR, Samira DOMENEK, Sandra GUINAULT, ALAIN SOLLOGOUB, Cyrille DARGENT, Eric DELPOUVE, Nicolas
Publisher : Elsevier
The physical aging behavior of amorphous polylactide constrained against polystyrene in layers of 300 nm, thanks to the layer–multiplying co–extrusion process, was investigated by fast–scanning calorimetry (FSC). By cooling down the sample from the liquid state to the glassy one at very fast scanning rates, it was possible to investigate the structural relaxation of the polymer glass at high temperatures for which the time needed to reach the equilibrium was shortened. Therefore it was possible to perform the study of physical aging in experimental conditions providing an expanded view of the structural relaxation for short aging times. Taking benefit of this property, it was highlighted that the aging kinetics of polylactide occurred significantly slower in the multilayer film, in comparison with a bulk amorphous film. The process of recovery in the multilayer system was found to occur at similar rates, or even slower, than in a three–layer film in which polylactide reached its maximum extent of crystallinity. This was attributed to mobility hindrance that might be inherent to the extrusion conditions or associated with the presence of capped interfaces with polystyrene.
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2018

Squeal measurement with 3D Scanning Laser Doppler Vibrometer: handling of the time varying system behavior and analysis improvement using FEM expansion

Auteurs : MARTIN, Guillaume CHANCELIER, Thierry VERMOT DES ROCHES, Guillaume BALMES, Etienne
Publisher :
In the presence of squeal, Operational Deflection Shapes (ODS) are classically performed to analyze behavior. A simple numeric example is used to show that two real shapes should dominate the response. This justifies an ad-hoc procedure to extract main shapes from the real brake time measurements. The presence of two shapes is confirmed despite variations with wheel position and reproducibility tests. To obtain a high spatial density measurement, 3D Scanning Laser Doppler Vibrometer is interesting but leads to iterative measurements on a time-varying system. An algorithm to merge sequential measurement and extract main shapes is detailed. Even with a high-density 3D SLDV measurement, shapes characterizing the squeal event are still only known on accessible surfaces. Minimum Dynamic Residual Expansion (MDRE) is thus finally used to estimate motion on a full FE mesh which eases interpretation and highlights areas where the test and the model contain errors.
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2018

A Simple Model for Hardness and Residual Stress Profiles Prediction for Low-Alloy Nitrided Steel, Based on Nitriding-Induced Tempering Effects

Auteurs : THIBAULT, Simon SIDOROFF, Christine JÉGOU, Sébastien BARRALLIER, Laurent MICHEL, Grégory
Publisher :
Nitriding of low-alloy steels is widely used for gears and bear- ings in aerospace industry. Some highly stressed surfaces re- quire high nitrided depth, which involves long time/high tem- perature nitriding treatment. This study focused on identifying process parameter effects on hardness and residual stress pro- files in a large range of nitriding time and temperature. We demonstrate that core and case can be considered as two ma- terials, softening of which can be predicted by two tempering laws. In addition, a basic relationship was derived from the nitriding depth and a pseudo-diffusion coefficient, allowing prediction of the hardness profile. Residual stress results show that the diffusion controlled effect can also be used to predict residual stress profile affected depth. Likewise, the tempering controlled effect can be used to predict surface and maximum values of the residual stress profile.
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2018

From Architectured Materials to Large-Scale Additive Manufacturing

Auteurs : DIRRENBERGER, Justin
Publisher : Springer International Publishing
The classical material-by-design approach has been extensively perfected by materials scientists, while engineers have been optimising structures geometrically for centuries. The purpose of architectured materials is to build bridges across themicroscale ofmaterials and themacroscale of engineering structures, to put some geometry in the microstructure. This is a paradigm shift. Materials cannot be considered monolithic anymore. Any set of materials functions, even antagonistic ones, can be envisaged in the future. In this paper, we intend to demonstrate the pertinence of computation for developing architectured materials, and the not-so-incidental outcome which led us to developing large-scale additive manufacturing for architectural applications.
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2018

Representative volume element size determination for viscoplastic properties in polycrystalline materials

Auteurs : YANG, Shaobo DIRRENBERGER, Justin MONTEIRO, Eric RANC, Nicolas
Publisher : Elsevier BV
The size of representative volume element (RVE) for 3D polycrystalline material is investigated. A statistical RVE size determination method is applied to a Voronoi tessellation-based pure copper microstructure. The definition of RVE has remained problematic in the literature for properties related to nonlinear viscoplastic behavior, e.g. apparent viscoplastic parameter, intrinsic plastic dissipation. Computational homogenization for elastic and plastic properties is performed within a crystal plasticity finite element framework, over many realizations of the stochastic microstructural model, using periodic boundary conditions. The generated data undergoes statistical treatment, from which RVE sizes are obtained. The method used for determining RVE sizes was found to be operational, even for viscoplasticity. The microscale analysis of the full-field simulation results reveals microstructure-related heterogeneities which shed new light on the problem of RVE size determination for nonlinear properties.
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2018

Large-Scale Additive Manufacturing of Ultra-High-Performance Concrete of Integrated Formwork for Truss-Shaped Pillars

Auteurs : GAUDILLIÈRE, Nadja DUBALLET, Romain BOUYSSOU, Charles MALLET, Alban ROUX, Philippe ZAKERI, Mahriz DIRRENBERGER, Justin
Publisher : Springer International Publishing
In the present paper a new additive manufacturing processing route is introduced to produce ultra-high-performance concrete complex architectonic elements, by printing integrated formwork. Interdisciplinary work involving material science, computation, robotics, architecture and design resulted in the development of an innovative way of 3D printing cementitious materials. The 3D printing process involved is based on a FDM-like technique, in the sense that a material is deposited layer by layer through an extrusion printhead mounted on a 6-axis robotic arm. An architectural application is used as a case-study to demonstrate the potentialities of the technology. Along with the detailed description of the design and construction process, a description of the responsibilities and their distribution amongst the stakeholders involved in the project is given. The steps taken to include the 3D printed element in an authorized regulatory context are presented as well. The structural elements produced constitute some of the largest 3D printed concrete parts available until now. Multi-functionality was enabled for structural elements by taking advantage of the complex geometry which can be achieved using our technology for large-scale additive manufacturing. The proposed process succeeds in solving several of the current issues problems that can be found in the production of 3D printed architectural features for an AEC industrial context and therefore suggests an immediately viable route for industry assimilation.
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2018

3D printing using concrete extrusion: A roadmap for research

Auteurs : BUSWELL, Richard A. LEAL DE SILVA, Wilson R. JONES, S.Z. DIRRENBERGER, Justin
Publisher : Elsevier BV
Large-scale additive manufacturing processes for construction utilise computer-controlled placement of extruded cement-based mortar to create physical objects layer-by-layer. Demonstrated applications include component manufacture and placement of in-situ walls for buildings. These applications vary the constraints on design parameters and present different technical issues for the production process. In this paper, published and new work are utilised to explore the relationship between fresh and hardened paste, mortar, and concrete material properties and how they influence the geometry of the created object. Findings are classified by construction application to create a matrix of issues that identifies the spectrum of future research exploration in this emerging field.
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2018

Propellant cohesive fracture during the peel test of a propellant/liner structure

Auteurs : TOULEMONDE, Paul-Aymé GILORMINI, Pierre JULIE, Diani DESGARDIN, Nancy NEVIÈRE, Robert
Publisher : Taylor and Francis Inc.
The integrity of propellant/liner structures in rocket motors is critical to ensure controlled combustion of the engine. In an effort to improve the bonding between the liner and the propellant, it is necessary to characterize it well. Therefore, a propellant–liner structure, bounded thanks to co-curing, has been submitted to a peel test while recording the macroscopic fracture energy and the local displacement field on the propellant-free surface. The experimental setup includes two cameras in order to record the displacement field on the propellant-free surface. Upon loading, the peel force stabilizes quickly due to a cohesive fracture in the propellant, providing access to the fracture energy. While the crack propagates through the propellant, it is observed that only a small localized area is submitted to strain, and most of the structure remains unstrained.
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2018

Influence of outer-layer finite-size effects on the dewetting dynamics of a thin polymer film embedded in an immiscible matrix

Auteurs : CHEBIL, Mohamed Souheib MCGRAW, Joshua D. SALEZ, Thomas SOLLOGOUB, Cyrille
Publisher :
In capillary-driven fluid dynamics, simple departures from equilibrium offer the chance to quantitatively model the resulting relaxations. These dynamics in turn provide insight on both practical and fundamental aspects of thin-film hydrodynamics. In this work, we describe a model trilayer dewetting experiment elucidating the effect of solid, no-slip confining boundaries on the bursting of a liquid film in a viscous environment. This experiment was inspired by an industrial polymer processing technique, multilayer coextrusion, in which thousands of alternating layers are stacked atop one another. When pushed to the nanoscale limit, the individual layers are found to break up on time scales shorter than the processing time. To gain insight on this dynamic problem, we here directly observe the growth rate of holes in the middle layer of the trilayer films described above, wherein the distance between the inner film and solid boundary can be orders of magnitude larger than its thickness. Under otherwise identical experimental conditions, thinner films break up faster than thicker ones. This observation is found to agree with a scaling model that balances capillary driving power and viscous dissipation with a no-slip boundary condition at the solid substrate/viscous environment boundary. In particular, even for the thinnest middle-layers, no finite-size effect related to the middle film is needed to explain the data. The dynamics of hole growth is captured by a single master curve over four orders of magnitude in the dimensionless hole radius and time, and is found to agree well with predictions including analytical expressions for the dissipation.
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