摘要:

The propagation of small‐amplitude stress discontinuities in linear, isotropic, in‐homogeneous viscoelastic media whose behavior is governed by integral stress‐strain laws is considered. The formulation is in terms of creep functions of virtually arbitrary type. A formal ray‐series asymptotic approach is developed which allows for the construction of wavefront solutions given either creep or relaxation functions for the medium. The advantages of these methods for obtaining numerical results are then clearly demonstrated.

ISSN:0148-6055    

DOI:10.1122/1.549671

出版商:The Society of Rheology    

年代:1982

数据来源: AIP

摘要:

In spite of the fact that extending oils have been used very widely for many years, no fundamental work has been done to elucidate how they affect the viscoelastic behavior of elastomers. We have performed viscoelastic measurements of the oil‐polymer system over the range of polymer concentration from 2.5 to 100% and temperature range from 30 to 150°C. Polymers were ethylene‐propylene copolymer rubbers, which had been chosen to represent very different chain structures. Sample A had a relatively narrow distribution of molecular weight (MWD) and the least branching, whereas sample B had a broader MWD with some long branching and gels. The temperature‐superposition principle was determined to be applicable for these data, allowing the construction of master curves of elastic and loss moduli over eight decades of frequency. The data encompass the rubbery plateau and flow regions. We have discovered that the concentration superposition applies to only a limited range of data, when the polymer contains long branching. Nevertheless, the two superposition principles provide a basic framework for describing the material behavior, especially when the significance is attached to the manner of deviation from the concentration superposition.

ISSN:0148-6055    

DOI:10.1122/1.549672

出版商:The Society of Rheology    

年代:1982

数据来源: AIP

摘要:

Rheometric data of a thixotropic bentonite suspension were used for the identification of selected rheological models of thixotropic flow behavior. Rheometric data, obtained for different deformation histories, were compared with theoretical predictions derived from the rheological model for the same deformation histories. At low shear rates, superanomalous behavior of the bentonite suspension has been observed. The capability of the rheological models to reproduce this unusual phenomenon is discussed. Torques necessary to agitate a thixotropic suspension by means of a small‐scale anchor agitator were calculated on the basis of the rheological equation and compared with torques obtained, for the same deformation histories, experimentally on the same agitator. Good agreement between theory and experiment has been found.

ISSN:0148-6055    

DOI:10.1122/1.549673

出版商:The Society of Rheology    

年代:1982

数据来源: AIP

摘要:

A theory for elastic fluids is developed using a tensor analogous to the Cauchy deformation measure to characterize the microstructure. The resulting mechanical theory is equivalent to that formally proposed by Hand. A free energy function is introduced and the constitutive functions are required to satisfy a dissipation inequality in any possible motion. Sufficient conditions for satisfying this inequality are obtained for constitutive functions that are linear in the rate of deformation. Several molecular theories of suspensions that are of this form appear to be inconsistent with some of these conditions. A particular theory that satisfies the dissipation inequality is analyzed in steady shear and elongational flows. This five‐constant model describes a shear‐thinning fluid with a nonvanishing extinction angle at high shear rates. Yield phenomena exhibited by some suspensions can be incorporated easily here through the material parameters.

ISSN:0148-6055    

DOI:10.1122/1.549674

出版商:The Society of Rheology    

年代:1982

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549694

出版商:The Society of Rheology    

年代:1982

数据来源: AIP