Publications

2018

Thermomechanical analysis induced by interrupted cutting of Ti6Al4V under several cooling strategies

Authors : LEQUIEN, Pierre POULACHON, Gérard OUTEIRO, José
Publisher : Elsevier BV
Cryogenic machining has mainly investigated in continuous cutting. Therefore, there is a lack of knowledge on the application of this technology to interrupted cutting, such as in milling. This study aims to investigate the thermomechanical phenomena in interrupted cutting of Ti6Al4V alloy under cryogenic, flood cooling and dry conditions. Due to the complexity of the thermomechanical analysis in milling, a special designed experimental setup has been developed through interrupted turning tests. This work highlights the influence of cryogenic flow rate and cutting time/non-cutting ratio on tool temperature. The obtained results can be extrapolated to milling operation.
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2019

Texture control of 316L parts by modulation of the melt pool morphology in selective laser melting

Authors : ANDREAU, Olivier KOUTIRI, Imade PEYRE, Patrice PENOT, Jean-Daniel SAINTIER, Nicolas PESSARD, Etienne DE TERRIS, Thibaut DUPUY, Corinne BAUDIN, Thierry
Publisher : elsevier
In this study, 316L parts were fabricated with the selective laser melting additive layer manufacturing process using unidirectional laser scan to control their texture. The melt pool shape, microstructure and texture of three different cubic samples were analyzed and quantified using optical microscopy and electron back-scattered diffraction. The samples scanned along the shielding gas flow direction were shown to exhibit shallow conduction melt pools together with a strong {110}<001> Goss texture along the laser scanning direction. The sample prepared with a laser scan perpendicular to the gas flow direction had deeper melt pools, with a weaker {110} <001> Goss texture in addition to a <100> fiber texture parallel to the scanning direction. Correlations were proposed between the melt-pool geometry and overlap and the resulting texture. The decrease of the melt pool depth was assumed to be linked to local attenuation of the laser beam effective power density transmitted to the powder bed.
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2019

Thermal behavior of poly(VDF-ter-TrFE-ter-CTFE) copolymers: Influence of CTFE termonomer on the crystal-crystal transitions

Authors : BARGAIN, François THUAU, Damien PANINE, Pierre HADZIIOANNOU, Georges DOMINGUES DOS SANTOS, Fabrice TENCE-GIRAULT, Sylvie
Publisher : elsevier
Depending on their CTFE content (from 0 to 10 mol %), poly (VDF-ter-TrFE-ter-CTFE), poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) copolymers exhibit ferroelectric (FE) or relaxor ferroelectric (RFE) properties at low temperature whereas they all present paraelectric (PE) behavior at high temperature. This thermal evolution of their electro-active properties is related to reversible crystal-crystal transitions. We studied these structural transitions for three different copolymers with various amount of CTFE (0, 4.4 and 9.7 mol %) using simultaneous SAXS-WAXS experiments along thermal cycles. We identified two types of crystalline phase at low temperature with their proper crystal-crystal transition: the first one containing all-trans conformations (orthorhombic FE phase) has a discontinuous transition towards the hexagonal PE phase, the second one which incorporates gauche disordered conformations (orthorhombic DFE (Defective Ferroelectric) or RFE) transits continuously towards the same hexagonal PE phase. For the intermediate composition (4.4 mol % CTFE), we observe the coexistence of these two simultaneous phase transitions, one discontinuous (FE to PE) and one continuous (RFE to PE), whereas only the continuous one exists in the higher CTFE composition (9.7 mol %). Relaxor ferroelectric properties are precisely observed in the temperature range of the structural RFE to PE transition [0 °C, 40 °C], highlighting the importance of this crystal-crystal transition. By coupling electric displacement−electric field (D−E) loop measurements, thermo-mechanical experiments (DSC and DMA) and dielectric spectroscopy, we propose a model to explain this RFE-PE continuous crystal-crystal transition in terpolymers.
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2019

On the miscibility of PVDF/PMMA polymer blends: Thermodynamics, experimental and numerical investigations

Authors : AID, Sara EDDHAHAK, Anissa KHELLADI, Sofiane ORTEGA, Zaida CHAABANI, Sana TCHARKHTCHI, Abbas
Publisher : elsevier
In this paper the miscibility of PVDF/PMMA blends was studied using different approaches: experimental tests, thermodynamics and numerical simulation. The first part of this study is devoted to the experimental work and aims to investigate the miscibility of blends by different experimental techniques. First, blends of PVDF/PMMA at different ratios were compounded and characterized using physico-chemical and rheological methods. The effect of PMMA content on the crystallization behavior of PVDF in the blend was experimentally investigated. At a second stage, the thermodynamic interaction parameter of Flory-Huggins was evaluated as a function of the PMMA proportion in the blends based on the experimental data related to the PVDF melting point and enthalpy. Besides, a numerical method has been developed using Fluent Ansys software to describe the coalescence phenomenon under different scenarios of viscosity ratios and grain sizes of polymers. The confrontation of the code simulation results with the experimental and thermodynamic approaches has shown a good agreement for reproducing the behavior of miscible polymers as well as their aptitude to form a homogeneous blend.
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2019

Impact of water and thermal induced crystallizations in a PC/MXD6 multilayer film on barrier properties

Authors : MESSIN, Tiphaine MARAIS, Stéphane FOLLAIN, Nadège CHAPPEY, Corinne GUINAULT, Alain MIQUELARD-GARNIER, Guillaume DELPOUVE, Nicolas GAUCHER, Valérie SOLLOGOUB, Cyrille
Publisher : elsevier
A multilayer film composed of alternating layers of polycarbonate (PC) and poly(m-xylene adipamide) (MXD6) was elaborated by using an innovative multilayer coextrusion process. Quasi-continuous thin MXD6 layers (nanolayers) alternating with PC layers were successfully obtained. The PC/MXD6 multilayer film showed a confining effect of MXD6 exerted by PC layers leading to an improvement of barrier properties despite a low degree of crystallinity (X c < 10 wt%). In order to further improve the barrier performances, crystallization treatments induced by water and by heating were then applied on the multilayer film and allowed reaching around 30 wt% of crystallinity in MXD6 layers. To decouple crystallization and geometrical constraint effects on the barrier properties in the multilayer films, the two treatments were also applied on MXD6 films. Surprisingly, despite an increase of the degree of crystallinity from 6 to 26%, water crystallization did not permit to improve gas barrier performances of the MXD6 film nor into the PC/MXD6 multilayer film. On the other hand, thermal crystallization of MXD6 in the multilayer film seems to be a more efficient route to strongly decrease the gas and moisture permeability, up to 75% for nitrogen, 58% for oxygen, 84% for carbon dioxide and 43% for water.
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2019

On the Proper Generalized Decomposition applied to microwave processes involving multilayered components

Authors : TERTRAIS, Hermine IBANEZ PINILLO, Ruben BARASINSKI, Anais GHNATIOS, Chady CHINESTA, Francisco
Publisher : elsevier
Many electrical and structural components are constituted of a stacking of multiple thin layers with different electromagnetic, mechanical and thermal properties. When 3D descriptions become compulsory the approximation of the fields along the thickness direction could involve thousands of nodes. To circumvent the numerical difficulties that such a rich description imply, we recently propose an in-plane–out-of-plane separated representation with the aim of computing fully 3D solutions as a sequence of 2D problems defined in the plane and others (1D) in the thickness. The main contribution of the present work is the proposal of an efficient in-plane–out-of-plane separated representation of the double-curl formulation of Maxwell equations able to address thin-layer laminates while ensuring the continuity and discontinuity of the tangential and normal electric field components respectively at the plies interface
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2019

Scaling laws for the laser welding process in keyhole mode

Authors : FABBRO, Rémy
Publisher : elsevier
This study shows that the keyhole model derived for determining the scaling laws of keyhole depths for laser welding when high power incident laser beams are used (typically in the multi-kW incident power range), can be also applied to determine the melted depths observed during the Selective Laser Melting process, where much lower incident powers of typically few hundred watts are focused on very small focal spots. The solution of the thermal analysis of this keyhole configuration is described by only three independent dimensionless parameters that are also involved for the analysis of a more general problem of heat conduction using similar input parameters. This global approach and the keyhole model describing the process of laser welding have been also validated by analyzing the melted depths generated by the Selective Laser Melting process. The dependence of the melted depths on the operating parameters of this process has been established, as well as the formation thresholds of the keyhole.
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2019

Multiscale physicochemical characterization of a short glass fiber–reinforced polyphenylene sulfide composite under aging and its thermo-oxidative mechanism

Authors : PEIYUAN, Zuo TCHARKHTCHI, Abbas SHIRINBAYAN, Mohammadali FITOUSSI, Joseph BAKIR, Farid
Publisher : John Wiley and Sons Ltd
In this paper, the thermo-oxidation for a short glass fiber–reinforced polyphenylene sulfide (PPS/GF) composite was experimentally and theoretically studied by a wide range of physicochemical and mechanical techniques. The accelerated thermal aging temperatures were fixed at 100°C, 140°C, 160°C, 180°C, and 200°C. Firstly, the results of weight loss under aging indicate the formation of volatile products because of chain scission of end groups. Also, Fourier-transform infrared spectroscopy (FTIR) results suggest that the formation and accumulation of carbonyl group arising from the formation of hydroperoxides in oxidative propagation process. In all cases of different thermal oxidation temperatures, it is hard to observe some significant change about the concentration of carbonyl group during the induction time. This induction time depends inversely on the oxidation temperature. Moreover, the cross-linking and chain scissions exist together according to the results of rheological results and it is easier to see the cross-linking phenomenon at the beginning of oxidation while the chain scissions are more pronounced, with the oxidation process developing further. In aspect of mechanical properties, σ max increases at the beginning of oxidation because of cross-linking, and subsequently, the σ max always decreases because of thermo-oxidation of the PPS matrix. In addition, the detailed thermo-oxidation processes are fully discussed in the end of this study. A mechanistic schema has been proposed to present different oxidation reactions of PPS polymer and then a kinetic model has been extracted from this mechanism. Afterwards, the model has been verified by experimental results at different temperatures.
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2019

A model order reduction approach to create patient-specific mechanical models of human liver in computational medicine applications.

Authors : LAUZERAL, Nathan BORZACCHIELLO, Domenico KUGLER, Michael RÉMOND, Yves GEORGE, Daniel HOSTETTLER, Alexandre CHINESTA, Francisco
Publisher : elsevier
Background and objective: This paper focuses on computer simulation aspects of Digital Twin models in the medical framework. In particular, it addresses the need of fast and accurate simulators for the mechanical response at tissue and organ scale and the capability of integrating patient-specific anatomy from medical images to pinpoint the individual variations from standard anatomical models. Methods: We propose an automated procedure to create mechanical models of the human liver with patient-specific geometry and real time capabilities. The method hinges on the use of Statistical Shape Analysis to extract the relevant anatomical features from a database of medical images and Model Order Reduction to compute an explicit parametric solution for the mechanical response as a function of such features. The Sparse Subspace Learning, coupled with a Finite Element solver, was chosen to create low-rank solutions using a non-intrusive sparse sampling of the feature space. Results: In the application presented in the paper, the statistical shape model was trained on a database of 385 three dimensional liver shapes, extracted from medical images, in order to create a parametrized representation of the liver anatomy. This parametrization and an additional parameter describing the breathing motion in linear elasticity were then used as input in the reduced order model. Results show a consistent agreement with the high fidelity Finite Element models built from liver images that were excluded from the training dataset. However, we evidence in the discussion the difficulty of having compact shape parametrizations arising from the extreme variability of the shapes found in the dataset and we propose potential strategies to tackle this issue. Conclusions: A method to represent patient-specific real-time liver deformations during breathing is proposed in linear elasticity. Since the proposed method does not require any adaptation to the direct Finite Element solver used in the training phase, the procedure can be easily extended to more complex non-linear constitutive behaviors - such as hyperelasticity - and more general load cases. Therefore it can be integrated with little intrusiveness to generic simulation software including more sophisticated and realistic models.
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2019

Ultrafine versus coarse grained Al 5083 alloys: From low-cycle to very-high-cycle fatigue

Authors : LI, Meng ANCHAL, Goyal DOQUET, Véronique RANC, Nicolas COUZINIÉ, Jean-Philippe
Publisher : elsevier
The fatigue performance of coarse and ultrafine-grained (UFG) 5083 Al alloy were compared, from low to very high cycle fatigue. The UFG alloy exhibited cyclic hardening and predominant kinematic hardening. At high plastic strain amplitude (and only in this regime), it showed easier crack initiation and a lower fatigue resistance. Its resistance to HCF was hardly better than that of its coarse grained counterpart until 2.10 6 cycles, but 43% higher in VHCF, until 5.10 8 cycles. Beyond that point, internal crack initiation occurred, and the fatigue resistance of the UFG material decreased, which was explained using Fracture Mechanics.
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