摘要:

Instrument inertia can produce spurious effects in controlled‐stress rheometry whenever the imposed torque changes with time, as in step‐jump or ramp‐function programming of the torque. These errors are especially serious with samples of low to moderate viscosity, where spurious time‐dependent viscosities are found even with Newtonian samples. The usual way of dealing with this problem, that of slowing the speed change program sufficiently to eliminate errors caused by inertia, both lengthens the time of measurement and obscures any rapid thixotropic transformations. This paper analyzes errors due to instrument inertia for both step‐jump and ramp‐function programming in terms of an inertial response time β=KI/η, whereKis the usual instrument constant for the particular rotational geometry,Ithe moment of inertia of the rotating part of the instrument, and η the viscosity of the sample. It then shows that ramp times of the order of 400β are needed to reduce inertial errors to acceptable levels. Finally, the paper shows that these errors can be eliminated by subtracting the inertial torque from the imposed torque, thereby eliminating spurious effects even for ramp times less than 40β. The proposed method of correction is applicable to non‐Newtonian and viscoelastic samples in all rotational geometries, and to any programming of the imposed torque.

ISSN:0148-6055    

DOI:10.1122/1.550138

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550093

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

The Hamiltonian formulation of equations in continuum mechanics through a generalized bracket operation is shown here to reproduce a variety of incompressible viscoelastic fluid models, including the Giesekus model (with particular cases the upper‐convected Maxwell and the Oldroyd‐B models), the FENE–P dumbbell, the Phan‐Thien/Tanner, the Leonov, the Bird/DeAguiar, and the bead–spring chain models. The analysis allows comparison of the differential models on a more fundamental level than previously possible by reformulating the equations in terms of the Hamiltonian (system energy) and the dissipation of the system expressed as functionals involving the velocity vector and structural parameter(s). In fact, all of these models involve only slight variations of the same general Hamiltonian and the dissipation tensor. An advantage of this formulation is the establishment of thermodynamic admissibility criteria which in complex flows can shed light on the range of validity and/or faithfulness of the numerical calculations involving the above models. The usefulness of the generalized bracket formulation lies in the systematic approach that it provides in addressing one of the fundamental problems that the engineer working with complex materials has to deal with: how to transfer information that has been painstakingly provided by the physical chemist, addressing fundamental problems on a molecular level, from the microscopic scale to the macroscopic level where the engineer actually needs the model in dealing with everyday industrial problems. It is hoped that this new formulation can be used in the future to systematically generate continuum constitutive models, which are thermodynamically consistent, and based on microscopic analysis. Thus, it is the purpose here to narrow the gap between detailed (molecular) microscopic descriptions of the motions of polymer chains and (macroscopic phenomenological) continuum approaches. We believe that the generalized bracket formulation, due to its inherent simplicity and symmetry, has the potential to provide an answer to very complex situations, such as multicomponent structured media and coupled transport phenomena.

ISSN:0148-6055    

DOI:10.1122/1.550094

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

The presence of significant amounts of adsorbed water on the particulate phase of most electrorheological (ER) materials is essential to their performance. This paper presents evidence showing that alumino‐silicate particles, when used as the dispersed component, produce ER active fluids without the apparent need for any water, adsorbed or structured. It is suggested that these materials by virtue of their unique chemistry and morphology, contain an intrinsic mechanism for producing their ER activity which does not require water. The ER activity and bulk conductivity of alumino‐silicate based and silica gel based ER fluids are examined as a function of water content. Whereas the silica gel based fluid loses its ER activity between 1.5% and 6% H2O, the alumino‐silicate based fluid continues to function at levels of H2O below FTIR detectability. Further, bulk current densities reach a constant value at around 0.5% H2O and below, but the fluids continue to operate without change. This suggests that models relying on increased interfacial polarization as a consequence of increased surface conductivity by ‘‘water coated’’ particles may not apply to Al–Si ER fluids. Most importantly it suggests that the ER activity of these materials is an inherent property of their chemistry and morphology.

ISSN:0148-6055    

DOI:10.1122/1.550095

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

Results are presented for light scattering studies of suspensions in a liquid of nearly hard colloidal spheres. Interparticle ordering or microstructure is determined for samples in equilibrium and undergoing both steady and oscillatory shear flows. Four basic structures are found to exist under these conditions: liquid‐like or amorphous, string‐like, sliding or randomly stacked layers, and face centered cubic. The conditions leading to these different microstructures is examined systematically and compared with predictions of microstructure for atomic and molecular or colloidal suspensions undergoing steady shear flow. Generally we find that ordering into layers at a finite shear rate is more pronounced as the volume fraction of particles increases. Equilibrium liquid‐like samples do not evidence a transition into a layer structure with increasing shear rate, and equilibrium crystalline samples do evidence a shear resisting face centered cubic ordering at small shear rates. For oscillatory shear flows we find that equilibrium liquid‐like samples could be induced to have a face centered cubic structure or layer structure depending on the amplitude and frequency of the shear flow. A microstructure phase diagram as a function of volume fraction of particles and oscillatory shear amplitude is constructed and compared with a simple model based on a strained face centered cubic lattice. Studies are presented which demonstrate the effect of shear history in producing desired microstructures.

ISSN:0148-6055    

DOI:10.1122/1.550096

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

摘要:

Measurements are reported for air drag on fine filaments in the melt blowing process. The data are fit well by this relation of the Matsui form:Cf=0.78 (ReD)−0.61. A wide range of conditions were used: filament diameters ranged from 13 to 305 μ, gas velocities ranged from 36 to 300 m/s (18 000 m/min), and fiber Reynolds numbers ranged from 15 to 3000. This is a higher and broader range of conditions than has previously been investigated.

ISSN:0148-6055    

DOI:10.1122/1.550097

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550098

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550099

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550100

出版商:The Society of Rheology    

年代:1990

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.550141

出版商:The Society of Rheology    

年代:1990

数据来源: AIP