Prediction of Hot Tear Formation in Vertical DC Casting of Aluminum Billets Using a Granular Approach

A coupled hydromechanical granular model aimed at predicting hot tear formation and stress-strain behavior in metallic alloys during solidification is applied to the semicontinuous direct chill casting of aluminum alloy round billets. This granular model consists of four separate three-dimensional (3D) modules: (I) a solidification module that is used for generating the solid-liquid geometry at a given solid fraction, (II) a fluid flow module that is used to calculate the solidification shrinkage and deformation-induced pressure drop within the intergranular liquid, (III) a semisolid deformation module that is based on a combined finite element/discrete element method and simulates the rheological behavior of the granular structure, and (IV) a failure module that simulates crack initiation and propagation. To investigate hot tearing, the granular model has been applied to a representative volume within the direct chill cast billet that is located at the bottom of the liquid sump, and it reveals that semisolid deformations imposed on the mushy zone open the liquid channels due to localization of the deformation at grains boundaries. At a low casting speed, only individual pores are able to form in the widest channels because liquid feeding remains efficient. However, as the casting speed increases, the flow of liquid required to compensate for solidification shrinkage also increases and as a result the pores propagate and coalesce to form a centerline crack

Modeling of Stress, Distortion, and Hot Tearing

International audienceComputational modeling of mechanical behavior during solidification is becoming more important. Thermal and microstructural simulations alone are insufficient to predict the quality of the final product that is desired by the casting industry. Accurate calculation of displacements, strains, and stresses during the casting process is needed to predict residual stress and distortion and defects such as the formation of cracks such as hot tears. It also helps predict porosity and segregation. As computing power and software tools for computational mechanics advance, it is becoming increasingly possible to perform useful mechanical analysis of castings and these important related behaviors

Numerical Investigation of an RCCI engine fueled with natural gas/dimethyl-ether in various injection strategies

Copyright: © 2021 by the authors. Reactivity control compression ignition engines illustrated suitable abilities in emission reduction beside high thermal efficiency. In this research, nine various direct fuel injection strategies were studied numerically: three cases with single injection strategy and six cases with split injection and different start of injection (SOI). In all simulated cases, equivalence ratio kept constant (i.e., 0.3). Among various strategies, single injection showed higher IMEP as a factor of efficiency with about 5.39 bar that occurred at SOI = 60 before top dead center (bTDC), while lower efficiency was observed for split injection case with 50%-50% injections of fuel in each injection stage. Start of combustion (SOC), burn duration and CA50 as factors for combustion characteristics were affected with SOI changes. In single SOI strategies, more advanced injection caused more advanced SOC where there was about 1.3 CAD advancing from 40 to 80 bTDC injection. Spilt SOI showed more advanced SOC, which, also more advanced, was allocated to 50%-50% split injection strategy. There was also the same trend in CA50 changes during change in SOI. Burn duration variations were insignificant and all of them approximately close to 4.5 CAD. According to the emissions researched in this study (Nitrogen Oxides (NOx), monoxide carbon (CO) and unburned hydro carbons (UHC)), all of these pollutants are below euro six diesel standards. Contours of emissions show that there were appropriate SOI for each case study, which were 45 degree bTDC for single strategy, 48 degree bTDC for 80%-20% mass injection and 70 degree bTDC for 50%-50% cases

Two-phase modelling of hot tearing in aluminium alloys using a semi-coupled method

Hot tearing is one of the most severe defects observed in castings, e.g. in billets or sheet ingots of aluminum alloys produced by DC casting. It is due to both tensile strains and a lack of interdendritic feeding in the mushy zone. In order to predict this phenomenon at the scale of an entire casting, the two-phase averaged conservation equations for mass and momentum must be solved in the mushy (i.e. mixed solid and liquid) region of the material. In recent contributions, M'Hamdi et al [1] proposed a strongly coupled resolution scheme for this set of equations. The solution of the problem was obtained using a rheological model established by Ludwig et al [2] and that captures the partially cohesive nature of the mushy alloy. In the present contribution, the problem is addressed using a slightly different approach. The same rheological model (i.e. saturated porous media treatment) is used, but the influence of the liquid pressure is neglected at this stage. This assumption allows for a weakly coupled resolution scheme in which the mechanical problem is first solved alone using ABAQUS™ and user subroutines. Then the pressure in the liquid phase is calculated separately accounting for the viscoplastic deformation of the porous solid skeleton and solidification shrinkage. This is done with a code previously developed for porosity calculations, and that uses a refined mesh in the mushy zone [3]. This semi-coupled method was implemented and its numerical convergence studied from the point of view of both time step and mesh size. Guidelines for selecting these numerical parameters as well as the conditions under which the semi-coupled method may be applied are provided. The model was then applied to three cases, i.e. two tensile tests conducted on mushy alloys [4, 5] and the casting of an entire billet [6]. Experimental data was indeed available concerning these problems prior to the present work. This information was used for the validation of the thermal and mechanical models that were setup to describe these different cases. The results of the semi-coupled approach were also used to describe in more details these different castings. First of all, the numerical study of the mushy zone tearing test [5] proved helpful for distinguishing different fracture modes. The role of the high strain rate applied to the mushy alloy in this case was also outlined. Another tensile test, referred to as the rig test [4], was successfully modeled in the present framework. The numerical results could be used to quantify the redistribution of strain in the mushy sample. As a consequence, intrinsic properties of the material, such as its ductility, could be extracted from the results. This study also gave further insight about the conditions under which tearing occurs in the samples. Finally, the semi-coupled method was used to study the DC casting process. In this case, a real process performed under realistic conditions for the production of an industrial scale billet was modeled. As it is more complex and difficult to characterize experimentally, the conditions for hot tearing formation are less accessible. However, the isotherm velocity, the strain, the strain rate and the liquid pressure could be described reasonably accurately. It was thus possible to correlate experimental observations of the hot tear with various calculated indicators of hot tearing susceptibility. Even with this information, it remains difficult to formulate new hot tearing criteria because all the indicators follow a similar trend during the casting and their respective contributions can thus not be distinguished. The present work showed that the level of accuracy and detail that can be reached using two-phase models with appropriate materials properties and boundary conditions is satisfactory. It is indeed possible to model the relevant phenomena (heat flow, solid deformation and liquid feeding) at the scale of an entire casting. The variation of the different simulated fields can be described down to a scale of the order of a few millimeters. In that sense, this approach is one important aspect required to build a multiscale model for the problem of hot tearing. It is expected that coupling such a method with granular models (which cover length scales from a few microns to a few centimeters [7]) will allow for a more complete description of the phenomena at hand. In the future, the development of such a multiscale numerical tool may prove to be the most efficient way towards quantitative predictions of hot tearing formation in real solidification processes

Modelling of defects in aluminium cast products

Over the last 4 decades, remarkable progress has been made in the modelling of casting processes. The development of casting models is well reflected in the proceedings of the 15 Modelling of Casting, Welding and Advanced Solidification Processes (MCWASP) conferences that have been held since 1980. Computer simulations have enabled a better understanding of the physical phenomena involved during solidification. Modelling gives the opportunity to uncouple the physical processes. Furthermore, quantities that are difficult or impossible to measure experimentally can be calculated using computer simulations e.g. flow patterns and recalescence. However, when it comes to accurately predicting casting performance and in particular, the occurrence of defects like cracks, segregation and porosity there is certainly some way to go. In this paper, the current understanding of the main mechanisms of defect formation during shape and DC casting processes will be reviewed and requirements will be discussed to give a direction to making casting models more predictive and quantitative

Use of Protein Crosslinking and Tandem Mass Spectrometry to Study the PsbO, PsbP and PsbQ Extrinsic Proteins of Higher Plant Photosystem II

Photosystem II (PSII) is a light-driven, water plastoquinone oxidoreductase present in all oxygenic photosynthetic organisms. The oxygen evolution process is catalyzed by the Mn4CaO5 cluster and an ensemble of intrinsic and extrinsic proteins which are associated with the photosystem. This metal cluster is stabilized and protected from exogenous reductants by the extrinsic proteins, PsbO, PsbP and PsbQ in higher plants, which are present on the lumenal face of PSII. No crystal structure for the higher plant PSII is currently available; consequently, the binding locations of these extrinsic proteins in PSII remain elusive. We have used chemical-crosslinkers Bis (sulfosuccinimidyl) suberate (BS3) and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) to crosslink the extrinsic proteins in their bound state to PSII followed by identification of the crosslinked products by tandem mass spectrometry. BS3 crosslinking identified the interacting domain of PsbP with PsbQ involving the PsbP residues 93Y, 96K and 97T (located in the 17-residue loop 3A, 89G-105S) which are in close proximity (\u3c11.4Å) to the N-terminal 1E residue of PsbQ. We also found that this PsbP assumes a compact structure from the nine independent crosslinked residues between the N- and C-terminus of PsbP. This suggests that the N-terminus of PsbP, 1A-11K (which is not resolved in the current crystal structures), is closely associated with the C-terminal domain 170K-186A. Additionally, interacting domains of two PsbQ copies from different PSII monomers were identified. The residue pairs 98K-133Y and 101K-133Y of PsbQ were crosslinked. These residues are \u3e30 Å apart when mapped onto the PsbQ crystal structure. Since BS3 can only crosslink residues which are within 11.4 Å, these residues are hypothesized as inter-molecular crosslinks of PsbQ. Furthermore, EDC crosslinking provided structural information pertaining to the organization of the N-terminus, absent in the cyanobacterial-PsbO. In this study, twenty-four crosslinked residues located in the N-terminal, loop and the β-barrel region of PsbO were identified. The models incorporating crosslinking data suggests several differences in cyanobacterial- and higher plant-PsbO. The results on extrinsic proteins provide significant new information concerning the association of the extrinsic proteins with PSII and are valuable while proposing overall models of higher plant PSII

Hope College Abstracts: 16th Annual Celebration of Undergraduate Research and Creative Performance

The 16th Annual Celebration of Undergraduate Research and Creative Performance was held on April 21, 2017 in the Richard and Helen DeVos Fieldhouse at Hope College and featured student-faculty collaborative research projects. This program is a record reflective of those projects between the 2016-2017 academic year

Hope College Abstracts: 15th Annual Celebration of Undergraduate Research and Creative Performance

The 15th Annual Celebration of Undergraduate Research and Creative Performance was held on April 15, 2016 in the Richard and Helen DeVos Fieldhouse at Hope College and featured student-faculty collaborative research projects. This program is a record reflective of those projects between the 2015-2016 academic year

Metrology Frame for Robotic Machining of Pockets in Large Flexible Panels

RÉSUMÉ Cette recherche présente une nouvelle technologie pour l'usinage robotisé de poches dans les grands panneaux flexibles. Pas d'articles pertinents ont été trouvés dans la littérature, mais un certain nombre de brevets examinés fournis certains des idées de base pour la conception. En particulier, il apparaît essentiel de soutenir le panneau où les forces d'usinage sont appliquées. Pour atteindre cet objectif, un cadre en C est proposé. En appliquant la méthode des éléments finis (MEF) tous les déplacements et les contraintes dans toute la structure sont évalués. Cela révèle que dû à l'effet des forces d'usinage, les deux branches de l'extrémité du cadre en C proposé dévient en sens inverse entraînant une ouverture importante du cadre en C. Pour mesurer cette déviation excessive, un cadre métrologique est conçu où un faisceau laser passe à travers les éléments optiques et atteint un photodétecteur. La position de la tache laser sur la surface du photodétecteur spécifie la distance momentanée entre les deux branches de l'extrémité du cadre en C. Toute déviation due à la force d'usinage affecte cette distance et sera donc détectée par la photodiode afin d'être compensée. Un prototype en bois du cadre en C est construit pour évaluer l'efficacité du cadre de métrologie optique. Les résultats indiquent que la déviation peut être mesurée avec une répétabilité de ± 0,1 mm et une exactitude de ± 0,0884 mm.----------ABSTRACT This thesis presents a new technology for the robotic machining of pockets in large and flexible panels. No relevant research papers were found in the literature but a number of patents are reviewed providing some basic for a conceptual design. In particular, it appears essential to support the panel where machining forces are applied. In order to achieve this goal, a C-frame is proposed. By applying FEA all of the displacements and stresses throughout the structure are evaluated. This reveals that due to machining forces, the two arms of the proposed C-frame deflect in opposite direction resulting in a significant opening of the C-frame. In order to measure this excessive deflection, a metrology frame is designed where a laser beam passes through optical elements and reaches a photodetector. The position of the laser spot on the photodetector surface specifies the momentary distance between the two arms of the C-frame. Any deflection due to machining force affects this distance and therefore will be sensed by the photodiode in order to be compensated. A small version of the C-frame is built from wood to assess the effectiveness of the optical metrology frame. Results indicate that the deflection can be measured with a repeatability of ±0.1 and precision of ±0.0884

Hybridation de méthodes numériques pour l'étude de la susceptibilité électromagnétique de circuits planaires

L'étude de la susceptibilité électromagnétique de circuits électroniques nécessite l'utilisation d'un outil de simulation rapide, précis et suffisamment flexible pour intégrer les dernières innovations technologiques. La méthode itérative basée sur le concept d'onde (notée WCIP pour Wave Concept Iterative Procedure) initialement proposée par H. Baudrand est particulièrement adaptée pour la modélisation numérique de circuits multicouches à plusieurs niveaux de métallisation. Pour ce type de circuits, elle se révèle être l'une des méthodes qui utilise le plus petit nombre d'inconnues pour atteindre une précision donnée. Néanmoins, la WCIP n'est pas adaptée à la prise en compte des diélectriques inhomogènes et des trous d'interconnexion. L'objectif de la thèse est de s'affranchir de ces limitations par un couplage avec des méthodes numériques volumiques. En premier lieu, l'hybridation a été mise en œuvre avec une méthode basée sur la théorie des lignes de transmission pour des raisons de correspondance de maillages. Par la suite, le couplage avec une technique d'éléments finis de type Galerkin Discontinu (notée GD) Hybridée permet d'atteindre des objectifs de précision et de rapidité car GD apporte une flexibilité dans la discrétisation. En effet, c'est une méthode d'éléments finis non conforme qui permet notamment de faire varier d'un élément à l'autre l'ordre polynomial d'approximation. On a ainsi développé une nouvelle méthode numérique hybride couplant la WCIP avec des méthodes volumiques qui offrent plus de souplesse pour la prise en compte des milieux complexes. Enfin, une stratégie de résolution par décomposition de domaines est également abordée à la fin du manuscrit