A model comparison to predict heat transfer during spot GTA welding

The present work deals with the estimation of the time evolution of the weld fusion boundary. This moving boundary is the result of a spot GTA welding process on a 316L stainless steel disk. The estimation is based on the iterative regularization method. Indeed, the three problems: direct, in variation and adjoint, classically associated with this method, are solved by the finite element method in a two-dimensional axisymmetric domain. The originality of this work is to treat an experimental estimation of a front motion using a model with a geometry including only the solid phase. In this model, the evolution of this solid domain during the fusion is set with the ALE moving mesh method (Arbitrary Lagrangian Eulerian). The numerical developments are realized with the commercial code Comsol Multiphysics® coupled with the software Matlab®. The estimation method has been validated in a previous work using theoretical data ([1]). The experimental data, used here for this identification are, temperatures measured by thermocouples in the solid phase, the temporal evolution of the melt pool boundary observed at the surface by a fast camera and the maximal dimensions of the melted zone measured on macrographs. These experimental data are also compared with numerical results obtained from a heat and fluid flow model taking into account surface tension effects, Lorentz forces and the deformation of the melt pool surface under arc pressure

Generation and characterization of T40/A5754 interfaces with lasersPatrice

Laser-induced reactive wetting and brazing of T40 titanium with A5754 aluminum alloy with 1.5 mm thickness was carried out in lap-joint configuration, with or without the use of Al5Si filler wire. A 2.4 mm diameter laser spot was positioned on the aluminum side to provoke spreading and wetting of the lower titanium sheet, with relatively low scanning speeds (0.1–0.6 m/min). Process conditions did not play a very significant role on mechanical strengths, which were shown to reach 250–300 N/mm on a large range of laser power and scanning speeds. In all cases considered, the fracture during tensile testing occurred next to the TiAl3 interface, but in the aluminum fusion zone. The interfacial resistance was then evaluated with the LASAT bond strength tester, based upon the generation and propagation of laser-induced shock waves. A 0.68 GPa uniaxial bond strength was estimated for the T40/A5754 interface under dynamic loading conditions

Solving Stefan problem through C-NEM and level-set approach

Numerical methods to solve problems involving discontinuities (jumps, kinks or singularities) on moving internal boundaries have received much attention over the last decade. Among them, the most suitable is probably the extended finite element method (XFEM) in tandem with the level-set technique due to its ability to take into account these discontinuities without matching meshes [1]. The present contribution aims to elaborate a numerical approach to model interfacial discontinu- ities within a meshless context. This approach couples the constrained natural element method (C-NEM) [2] and the level-set technique. In the former, the natural neighbours interpolation, based on a Voronoi diagram, is locally enriched through the partition of unity concept. This enrichment is built from level-set functions that represent and track implicitly discontinuities inside the domain [3]. Like in XFEM, key features of the proposed approach is (i) to determine the intersection between Voronoi cells and discontinuities and (ii) to integrate numerically the weak form over cells containing discontinuities. After testing the proposed method on classical benchmarks, both accuracy and efficiency are examined on the two phase Stefan problem that deals with heat flow involving a solid-liquid phase boundary on which a jump condition must be satisfied [4]. [1] Chessa J., Smolinski P. and Belytschko T. The extended finite element method (XFEM) for solidification problems. Int. J. Numer. Meth. Engng 53:1959–1977 (2002). [2] Yvonnet J., Chinesta F., Lorong P. and Ryckelynck D. The constrained natural element method (C-NEM) for treating thermal models involving moving interfaces. Int. J. Therm. Sci. 44:559–569 (2005). [3] LiuJ.T.,GuS.T.,MonteiroE.andHeQ.C.Aversatileinterfacemodelforthermalconduc- tion phenomena and its numerical implementation by XFEM. Comp. Mech. 53:825–843 (2014). [4] Carslaw H.S. and Jaeger J.C. Conduction of Heat in Solids. 2th Edition, Clarendon Press, (1959)

[INVITED] An overview of the state of art in laser welding simulation

The work presented in this paper deals with the laser welding simulation. Due to the rise of laser processing in industry, its simulation takes also more and more place. Nevertheless, the physical phenomena occurring are quite complex and, above all, very coupled. Thus, a state of art is necessary to summarize phenomena that have to be considered. Indeed, the electro-magnetic wave interacts with the material surface, heating the piece until the fusion and the vaporization. The vaporization induces a recoil pressure and deforms the liquid/vapor interface creating a vapor capillary. The heat diffused in the material produces thermal dilatation leading to mechanical stress and strain. As a complete simulation is too large to be computed with one model, the literature is composed by two kinds of models, the thermo-mechanical simulations and the multi-physical simulations. The first aims to find the mechanical stress and strain due to the welding. The model is usually simplified in order to reduce the simulation size. The second, compute the more accurately the thermal and the velocity fields. In that case authors usually search also the size of the weld bead and want to be totally self consistent. In this review, the major part of equations and assumptions needed to simulate laser welding are shown. Their effects on simulation results are illustrated for each simulation type. The paper aims to give sufficient knowledge and tools to allow a simulation of laser weldin

Multiphysics Simulation and Experimental Investigation of Aluminum Wettability on a Titanium Substrate for Laser Welding-Brazing Process

The control of metal wettability is a key-factor in the field of brazing or welding-brazing. The present paper deals with the numerical simulation of the whole phenomena occurring during the assembly of dissimilar alloys. The study is realized in the frame of potential applications for the aircraft industry, considering the case of the welding-brazing of aluminum Al5754 and quasi-pure titanium Ti40. The assembly configuration, presented here, is a simplification of the real experiment. We have reduced the three-dimensional overlap configuration to a bi-dimensional case. In the present case, an aluminum cylinder is fused onto a titanium substrate. The main physical phenomena which are considered here are: the heat transfers, the fluid flows with free boundaries and the mass transfer in terms of chemical species diffusion. The numerical problem is implemented with the commercial software Comsol Multiphysics™, by coupling heat equation, Navier-Stokes and continuity equations and the free boundary motion. The latter is treated with the Arbitrary Lagrangian Eulerian method, with a particular focus on the contact angle implementation. The comparison between numerical and experimental results shows a very satisfactory agreement in terms of droplet shape, thermal field and intermetallic layer thickness. The model validates our numerical approach

t(5;9)(q14.1;p24) SSBP2/JAK2

Review on t(5;9)(q14.1;p24) SSBP2/JAK2, with data on clinics, and the genes implicated

Solving Stefan problem through C-NEM and level-set approach

Numerical methods to solve problems involving discontinuities (jumps, kinks or singularities) on moving internal boundaries have received much attention over the last decade. Among them, the most suitable is probably the extended finite element method (XFEM) in tandem with the level-set technique due to its ability to take into account these discontinuities without matching meshes [1]. The present contribution aims to elaborate a numerical approach to model interfacial discontinu- ities within a meshless context. This approach couples the constrained natural element method (C-NEM) [2] and the level-set technique. In the former, the natural neighbours interpolation, based on a Voronoi diagram, is locally enriched through the partition of unity concept. This enrichment is built from level-set functions that represent and track implicitly discontinuities inside the domain [3]. Like in XFEM, key features of the proposed approach is (i) to determine the intersection between Voronoi cells and discontinuities and (ii) to integrate numerically the weak form over cells containing discontinuities. After testing the proposed method on classical benchmarks, both accuracy and efficiency are examined on the two phase Stefan problem that deals with heat flow involving a solid-liquid phase boundary on which a jump condition must be satisfied [4]. [1] Chessa J., Smolinski P. and Belytschko T. The extended finite element method (XFEM) for solidification problems. Int. J. Numer. Meth. Engng 53:1959–1977 (2002). [2] Yvonnet J., Chinesta F., Lorong P. and Ryckelynck D. The constrained natural element method (C-NEM) for treating thermal models involving moving interfaces. Int. J. Therm. Sci. 44:559–569 (2005). [3] LiuJ.T.,GuS.T.,MonteiroE.andHeQ.C.Aversatileinterfacemodelforthermalconduc- tion phenomena and its numerical implementation by XFEM. Comp. Mech. 53:825–843 (2014). [4] Carslaw H.S. and Jaeger J.C. Conduction of Heat in Solids. 2th Edition, Clarendon Press, (1959)

Laser-induced plume investigated by finite element modelling and scaling of particle entrainment in laser powder bed fusion

Although metal vaporisation has been observed in several laser processes such as drilling or welding, vapour plume expansion and its induced side effects are not fully understood. Especially, this phenomenon is garnering scientific and industrial interest since recent investigations in laser powder bed fusion (LPBF) have designated metal vaporisation as main source of denudation and powder spattering. The present study aims to provide a new insight on the dynamics of laser-induced vaporisation and to assess the potential of different gases for particle entrainment. A self-consistent finite element model of laser-induced keyhole and plume is thus presented for this purpose, built from a comprehensive literature review. The model is validated with dedicated experimental diagnostics, involving high-speed imaging to measure the ascent velocity of the vapour plume. The transient dynamics of vapour plume is thus quantified for different laser incident intensities and gas flow patterns such as the mushroom-like structure of the vapour plume are analysed. Finally, the model is used as a tool to quantify the entrainment flow expected in LPBF and an analytical model is derived to define a velocity threshold for particle entrainment, expressed in term of background gas properties. Doing so it is possible to predict how denudation evolves when the gaseous atmosphere is changed

Ultra-fast quantum randomness generation by accelerated phase diffusion in a pulsed laser diode

We demonstrate a high bit-rate quantum random number generator by interferometric detection of phase diffusion in a gain-switched DFB laser diode. Gain switching at few-GHz frequencies produces a train of bright pulses with nearly equal amplitudes and random phases. An unbalanced Mach-Zehnder interferometer is used to interfere subsequent pulses and thereby generate strong random-amplitude pulses, which are detected and digitized to produce a high-rate random bit string. Using established models of semiconductor laser field dynamics, we predict a regime of high visibility interference and nearly complete vacuum-fluctuation-induced phase diffusion between pulses. These are confirmed by measurement of pulse power statistics at the output of the interferometer. Using a 5.825 GHz excitation rate and 14-bit digitization, we observe 43 Gbps quantum randomness generation.This work was supported by the ERC under project MAMBO (Proof of Concept of PER- CENT) and project AQUMET, MINECO under projects FIS2011-23520, TEC2010-14832, and Explora INTRINQRA, Galician Regional Government under projects CN2012/279 and CN2012/260 “Consolidation of research units: AtlantTIC” and FEDER under project Ref: UPVOV10-3E-492.Peer ReviewedPostprint (published version

A Gaia early DR3 mock stellar catalog: Galactic prior and selection function

We present a mock stellar catalog, matching in volume, depth and data model the content of the planned Gaia early data release 3 (Gaia EDR3). We have generated our catalog (GeDR3mock) using galaxia, a tool to sample stars from an underlying Milky Way (MW) model or from N-body data. We used an updated Besan\c{c}on Galactic model together with the latest PARSEC stellar evolutionary tracks, now also including white dwarfs. We added the Magellanic clouds and realistic open clusters with internal rotation. We empirically modelled uncertainties based on Gaia DR2 (GDR2) and scaled them according to the longer baseline in Gaia EDR3. The apparent magnitudes were reddened according to a new selection of 3D extinction maps. To help with the Gaia selection function we provide all-sky magnitude limit maps in G and BP for a few relevant GDR2 subsets together with the routines to produce these maps for user-defined subsets. We supplement the catalog with photometry and extinctions in non-Gaia bands. The catalog is available in the Virtual Observatory and can be queried just like the actual Gaia EDR3 will be. We highlight a few capabilities of the Astronomy Data Query Language (ADQL) with educative catalog queries. We use the data extracted from those queries to compare GeDR3mock to GDR2, which emphasises the importance of adding observational noise to the mock data. Since the underlying truth, e.g. stellar parameters, is know in GeDR3mock, it can be used to construct priors as well as mock data tests for parameter estimation. All code, models and data used to produce GeDR3mock are linked and contained in galaxia_wrap, a python package, representing a fast galactic forward model, able to project MW models and N-body data into realistic Gaia observables.Comment: 22 pages, 20 figures, accepted by PASP, catalog info and download and ADQL interface: http://dc.g-vo.org/tableinfo/gedr3mock.main ; relevant github repositories: https://github.com/jan-rybizki/Galaxia_wrap ; https://github.com/jan-rybizki/gdr2_completenes