Flow behaviour of semi-solid metal alloys

Koke, J.; Modigell, Michael

doi:10.1016/s0377-0257(03)00080-6

Cited by 94 publications

(90 citation statements)

References 13 publications

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“…If the curve has as increasing slope with increasing shear rate, it represents shear-thickening behavior, and a decreasing slope with increasing shear rate is shear thinning. To obtain results which can be compared, a conditioning shear rate (i.e., the shear rate before the jump) has been identified which is common between the results of Koke and Modigell [25] (their Figure 18(b)) and the results of Liu et al [24] (their Table IV). The only common shear rate is 100 s À1 .…”

Section: B Methods Of Analysis In This Papermentioning

confidence: 99%

“…[30] Kumar et al [23,27] and Koke and Modigell [25,28] (with further analysis of Reference 28 by Burgos et al [29] ) find their material to be shear thickening during the transient, Quaak [22] and Liu et al [24] observe the material is shear thinning. Peng and Wang [26] study the behavior but do not state a conclusion.…”

Section: F Aim Of the Papermentioning

confidence: 99%

“…The time for the transient in shear rate is of the order of 10 ms in Kumar et al [23] and 100 ms in Liu et al [24] thus satisfying this requirement. The timescale for the transient in Koke and Modigell [25] is not stated but is short. Peng and Wang [26] have a transient time of 0.1 s. In practice, a purely isostructural jump will be impossible to achieve because some microstructural processes will always start to occur during the jump.…”

Section: Connection With Discontinuous Shear Thickening In Dense Smentioning

confidence: 99%

“…There is contradictory evidence in the literature [22][23][24][25][26][27][28][29] as to whether the behavior during rapid increases in shear rate is shear thinning or shear thickening, although it is clear that once in the die the material is thinning. [30] Kumar et al [23,27] and Koke and Modigell [25,28] (with further analysis of Reference 28 by Burgos et al [29] ) find their material to be shear thickening during the transient, Quaak [22] and Liu et al [24] observe the material is shear thinning.…”

Section: F Aim Of the Papermentioning

confidence: 99%

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Does Shear Thickening Occur in Semisolid Metals?

Atkinson

Favier

2016

Metall Mater Trans A

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In the various forms of semisolid processing such as thixoforming and thixoforging, the entry into the die occurs in a fraction of a second so it is the transient rheological behavior which governs the initial stages of flow. In experiments in the literature, this rheological behavior is probed through applying rapid transitions in shear rate under isothermal conditions. There is contradictory evidence as to whether the behavior during these transitions is shear thinning or shear thickening, although it is clear that once in the die the material is thinning. Here the data in the literature are reanalyzed to obtain a rationalization of the contradictions which has not previously been available. It is argued that if a suspension is initially in a disagglomerated state (i.e., one which is initially sheared), the instantaneous behavior with a jump-up in shear rate is shear thickening (even if the long-term steady-state behavior is shear thinning) provided the fraction solid is greater than about 0.36 and the final shear rate at the end of the jump is greater than about 100 s À1 . If the jump-up in shear rate is made from rest then yield masks the shear thickening.

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Section: B Methods Of Analysis In This Papermentioning

confidence: 99%

Section: F Aim Of the Papermentioning

confidence: 99%

Section: Connection With Discontinuous Shear Thickening In Dense Smentioning

confidence: 99%

Section: F Aim Of the Papermentioning

confidence: 99%

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Does Shear Thickening Occur in Semisolid Metals?

Atkinson

Favier

2016

Metall Mater Trans A

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“…Barnes [63][64][65] concluded that the presence of a yield stress as reported by some workers for thixotropic materials (but not semisolid alloys) is probably due to the limitations of their experimental apparatus in not being able to measure shear stresses at very low shear rates. Koke and Modigell [66] have used a shear stress controlled rheometer to measure yield stress directly on Sn 15%Pb. They distinguish between a static yield stress where the fluid is at rest prior to the application of a shear stress, and a dynamic yield stress where the fluid is being continuously sheared.…”

Section: Background Rheologymentioning

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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