摘要:

A general rheological model of a nonlinear viscoplastic solid is developed, affording better quantitative prediction of behavior of viscoplastic materials. Rheological properties are quantified in terms of three types of curves obtained by tests, commonly used for description of mechanical material properties: constant rate, force deformation, creep, and relaxation curves. The mathematical model is based on a characteristic nonlinear differential equation describing the mechanical properties of a material. This equation defines the forceFacting on a test specimen as composed of a cubic elasticity forceK0x+rx3,viscous damping forceCẋ,and internal friction forceFf (sgn ẋ).The elastic parameterK0quantifies linear elasticity while the strain hardening (or softening when negative) parameterraffords prediction of nonlinear behavior of the material. The viscous and Coulomb damping forces properly account for both rate‐dependent and rate‐independent energy dissipative properties of the material. Local linearization of the characteristic equation permits a closed‐form solution for creep at constant loading force and relaxation at constant deformation. The parameters of the nonlinear model can be read off or computed from practical curves, whereby a realistic link may be established between the mathematical model and real viscoplastic materials. The properties of a nonlinear viscoplastic solid are further clarified in terms of a time‐ and deformation‐dependent relaxation modulus. By setting the nonlinear parameters to zero the deformation‐independent linear relaxation modulus of a Boltzmann solid is obtained. It is believed that this model will afford better quantification of rheological properties of materials and improved interpretation of experimental data.

ISSN:0148-6055    

DOI:10.1122/1.549714

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

The molecular model used by Doi and Edwards in developing their rheological theory admits a simple form for the free energy of deformation, at least when the independent alignment approximation is used. A general expression is derived, as well as the specific form which applies to an instantaneous shear deformation. The latter is used to analyze the possibility that instabilities, or “deformational phase separations,” arise in the course of stress relaxation experiments. The results of the analysis are compared with recent experimental results by Osaki and Kurata and by Vrentas and Graessley which show an anomalous relaxation behavior.

ISSN:0148-6055    

DOI:10.1122/1.549715

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

The rise of an unsupported liquid column through the air from a quiescent pool to a capillary with suction (the “ductless siphon”) is interpreted approximately in terms of the elongational viscosity(η̄)of several solvents and dilute polymer solutions. The maximum height of siphon rise(h*)is used to characterize the ratioη̄/η,where η is shear viscosity, and an approximate hydrodynamic analysis showsη̄/η∼(h*)2.Measurements made for polyisobutylenes in toluene and jet fuel (kerosene), for a proprietary antimisting agent PX in jet fuel, and for polyethylene oxide and polyacrylamides in water show thath*depends on molecular variables as predicted by dilute‐solution theories forη̄/η.Polymer molecular weight range is0.8×106

ISSN:0148-6055    

DOI:10.1122/1.549726

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

摘要:

The isothermal spinline velocity profile is computed using the Doi‐Edwards constitutive equation, and the profile is found to be nearly the same as that for a corotational Maxwell fluid, for which an analytic solution exists. Both models predict limited spinnability, i.e., solutions exist for short spinlines and low draw ratios only. This behavior contrasts to that of the upper‐convected Maxwell model, for which threadlines of any length may be spun. The spinning behavior of the Doi‐Edwards model is dominated not by the distribution of relaxation times, but by the elongational strain measure.

ISSN:0148-6055    

DOI:10.1122/1.549716

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549727

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549728

出版商:The Society of Rheology    

年代:1983

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549729

出版商:The Society of Rheology    

年代:1983

数据来源: AIP