摘要:

Capillary rheometry was used to analyze the variations in end correctioneas a function of shear rate and temperature, in five different rubbers: natural polyisoprene Hevea and Guayule rubbers (HR and GR); synthetic polyisoprene high cis Ameripol SN‐600 and low cis IR‐309 (IR97 and IR92); and styrene‐butadiene copolymer SBR‐1503. For HR, GR, and IR97 the end correction increases as shear rate increases, up to a certain point beyond which the effect is reversed, i.e., the end correction decreases. This effect is detected at shear rates and temperatures near the occurrence of flow‐induced crystallization. This phenomenon was barely observed in IR92 and not observed in SBR. In addition, flow‐induced crystallization of these two rubbers (cessation of flow) was not observed, as it was in HR, GR, and IR97. Hence, these variations in end correction for HR, GR, and IR97 have been attributed to the occurrence of incipient flow‐induced crystallization.

ISSN:0148-6055    

DOI:10.1122/1.549707

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

Capillary rheometry was used to analyze the variations in end correction as a function of shear rate and temperature in various thermoplastics. For PP, HDPE, LDPE, and PS the end correction increases as shear rate increases, up to a certain point, beyond which the effect is reversed, i.e., the end correction decreases. These variations in the end correction have been attributed to the occurrence of incipient solidification of the flowing material, either because conditions are near those necessary for flow‐induced crystallization, as in PP, HDPE, and LDPE, or because conditions are near those necessary for the transition to the glassy state, as in PS.

ISSN:0148-6055    

DOI:10.1122/1.549708

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

The measurement and use of the flow properties of highly concentrated solid‐liquid suspensions is a topic of considerable practical interest in a broad spectrum of industries. The yield stress is a rheological property that all highly concentrated suspensions may have in common. In this work four established methods for determining the yield stress are compared with a fifth and new method based on a vane test developed in soil mechanics. It is clearly shown that a single‐point measurement with the vane device is sufficient to determine accurately the yield stress in a region of high concentration where the four conventional methods are extremely tedious or not applicable. Furthermore, the vane method does not rely on any previous shearing of a suspension and hence is applicable for study of the kinetics of thixotropic systems. The work has been motivated by the need to know the yield stress of highly concentrated bauxite residue suspensions in order to establish a waste disposal strategy for the residue which is a waste product in the production of alumina from bauxite.

ISSN:0148-6055    

DOI:10.1122/1.549709

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

The operator form of the constitutive equation containing fractional derivatives leads to an expression for the complex modulus which is a ratio of polynomials of fractional order in reduced frequency. A ratio of factored polynomials is developed by use of Bode diagrams; another related form arises from the generalized fractional Maxwell model. Bode diagrams are used to determine parameter values. Interconversion to other mechanical properties is outlined. The results potentially form the basis of a new theory.

ISSN:0148-6055    

DOI:10.1122/1.549710

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

Through thermodynamic arguments, it is shown that the rest state of a viscoelastic fluid with fading memory is stable to the class of retarded flow perturbations, for which the second‐order approximation to the stress isS=−pI+β0A1+β2A12+β1A2,even thoughβ10,β1+β2=0,β1⩾0.In the absence of the latter two conditions, asymptotic stability is not assured.

ISSN:0148-6055    

DOI:10.1122/1.549711

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

A viscoelastic constitutive equation of the single‐integral form has been designed. Its memory function is factored into a time‐dependent part and a strain‐dependent part. The time function is the usual series of exponential relaxations. Its relaxation times and weighting coefficients are determined by nonlinear regression on linear viscoelastic data: stress relaxation after small‐strain and small‐amplitude sinusoidal oscillations. The relative accuracy of linear and nonlinear regression fitting is compared. The strain‐dependent function is new. It is of a simple sigmoidal form with only two parameters: one determined from shear and the other from extensional data. Its sigmoidal form provides a finite linear viscoelastic region, a steady viscosity in uniaxial extension, and a well‐behaved power‐law shear viscosity at high shear rate. An efficient strategy for collecting sufficient data to determine the parameters of the equation is described. Predictions of the equation are tested against shear and extension data collected on the Rheometrics System Four for two polydimethylsiloxanes and against data for other polymer melts from the literature. Both uniaxial and biaxial extension as well as shear data are described. Transient shear normal stresses are somewhat underpredicted. The constitutive equation has the potential for modeling mixed shear and extensional flows as encountered in processing operations and is simple enough to be attractive for efficient computer‐aided analysis by modern finite element methods.

ISSN:0148-6055    

DOI:10.1122/1.549712

出版商:The Society of Rheology    

年代:1983

数据来源: AIP