Constitutive modeling and characterization of the flow behavior of semi-solid metal alloy slurries—II. Structural evolution under shear deformation

Martin, Chantal; Kumar, Pratyush; Brown, Stuart B.

doi:10.1016/0956-7151(94)90427-8

Cited by 58 publications

(49 citation statements)

References 19 publications

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“…Many experiments were achieved in the last past two decades to characterize the semisolid rheology. However, many disparities appear between literature results [1][2][3][4][5][6][7]. As far as the steady-state is concerned, the presence of strong shear thinning behaviour is now well-admitted.…”

Section: Introductionmentioning

confidence: 96%

Transient semi-solid behaviour: modelling step-change up and step-change down in shear rate using a micromechanical approach

Favier

Manceau

2009

Int J Mater Form

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Thixoforming is a semi-solid metal forming process. It involves the transient behaviour of semisolids that depends on the solid fraction and the microstructure of the material before forming. Finite element simulations of thixoforming require constitutive equations accounted for this transient behaviour in relation with the material microstructure. In this paper, we propose a model based on a micromechanical approach and using homogenization techniques. It is an extension from a previous model initially developed to capture the isothermal and steady-state semisolid behaviour. We showed that the model describes very well the qualitative transient response highlighted via step-change up and step-change down in shear rate. In particular, the instantaneous response after a rapid change in shear rate is found to be associated with a constant internal structure and to follow a Newtonian behaviour. This result is in good agreement with some literature experimental results but contradicts others which reveal a shear thickening behaviour.

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Section: Introductionmentioning

confidence: 96%

Transient semi-solid behaviour: modelling step-change up and step-change down in shear rate using a micromechanical approach

Favier

Manceau

2009

Int J Mater Form

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“…Equation [14] carries some similarity with other evolution equations that have been proposed in the literature for characterizing a semisolid or a partially solidified alloy with an internal variable that accounts for the agglomeration between solid grains or the cohesion of the mush. [17,22] The rheological functions ␣(g s , X) and C* (g s , X) govern the evolution of C with macroscopic strain and depend both on the solid fraction and on the stress state (via the stress triaxiality X). The function ␣(g s , X) governs the evolution of C at small strains, whereas C* (g s , X) defines the saturation value of C at large strains.…”

Section: Evolution Equation For the Internal Variable Cmentioning

confidence: 99%

Rheological behavior of Al-Cu alloys during solidification constitutive modeling, experimental identification, and numerical study

Ludwig

Drezet

Martín³

et al. 2005

Metall Mater Trans A

131

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The rheological behavior of a solidifying alloy is modeled by considering the deforming material as a viscoplastic porous medium saturated with liquid. Since the solid grains in the mush do not form a fully cohesive skeleton, an internal variable that represents the partial cohesion of this porous material is introduced. The model parameters are identified using shear and compressive stress states under isothermal conditions on an Al-Cu model alloy. The model is partially validated with nonisothermal conditions and we complete this study with tensile conditions. Such conditions, when applied on the mush, may lead to severe defects in many casting processes. The model has been implemented into a commercial finite-element code to simulate a tensile test. Comparison with experimental data shows that the model is able to reproduce the main features of a solidifying alloy under tension, although fracture is not directly addressed here. We show that two critical solid fractions must be introduced in the model to account for the rheology: the coherency solid fraction at which the mush acquires significant strength and the coalescence solid fraction at which solid grains start to form solid bridges.

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“…the internal variable in the Brown et al Model [127][128][129] in Section 6.1). The permeability equation…”

Section: 32two Phase Finite Elementmentioning

confidence: 99%

Modelling the Semisolid Processing of Metallic Alloys

Atkinson

2005

ChemInform

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Semi-solid processing of metallic alloys and composites utilises the thixotropic behaviour of materials with non-dendritic microstructure in the semi-solid state. The family of innovative manufacturing methods based on this behaviour has been developing over the last twenty years or so and originates from scientific work at MIT in the early 1970s. Here, a summary is given of:-routes to spheroidal microstructures; types of semi-solid processing; and advantages and disadvantages of these routes.Background rheology and mathematical theories of thixotropy are then covered as precursors to the main focus of the review on transient behaviour of semi-solid alloy slurries and computational modelling. Computational Fluid Dynamics (CFD) can be used to predict die filling. However, some of the reported work has been based on rheological data obtained in steady state experiments, where the semi-solid material has been maintained at a particular shear rate for some time. In reality, in thixoforming, the slurry undergoes a sudden increase in shear rate from rest to 100s -1 or more as it enters the die. This change takes place in less than a second. Hence, measuring the transient rheological response under rapid changes in shear rate is critical to the development of modelling of die filling and successful die design for industrial processing. The modelling can be categorised as one phase or two phase and as finite difference or finite element. Recent work by Alexandrou and co-workers and, separately Modigell and co-workers, has led to the production of maps which, respectively summarise regions of stable/unstable flow and regions of laminar/transient/turbulent fill. These maps are of great potential use for the prediction of appropriate process parameters and avoidance of defects. A novel approach to modelling by Rouff and coworkers involves micro-modelling of the 'active zone' around spheroidal particles.There is little quantitative data on the discrepancies or otherwise between die fill simulations and experimental results (usually obtained through interrupted filling).There are no direct comparisons of the capabilities of various software packages to model the filling of particular geometries accurately. In addition, the modelling depends on rheological data and this is sparse, particularly for the increasingly complex two-phase models. Direct flow visualisation can provide useful insight and avoid the effects of inertia in interrupted filling experiments.

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Constitutive modeling and characterization of the flow behavior of semi-solid metal alloy slurries—II. Structural evolution under shear deformation

Cited by 58 publications

References 19 publications

Transient semi-solid behaviour: modelling step-change up and step-change down in shear rate using a micromechanical approach

Transient semi-solid behaviour: modelling step-change up and step-change down in shear rate using a micromechanical approach

Rheological behavior of Al-Cu alloys during solidification constitutive modeling, experimental identification, and numerical study

Modelling the Semisolid Processing of Metallic Alloys

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