摘要:

An analytical technique is developed to provide consistency in the experimental results obtained in creep and relaxation tests of linear viscoelastic materials. A characterization procedure, using exponential series, for creep and relaxation is presented. Conditions for the positiveness of the coefficients of the exponential series, which guarantee that the characterization is consistent with the physical behavior of the material, are derived.

ISSN:0148-6055    

DOI:10.1122/1.549129

出版商:The Society of Rheology    

年代:1969

数据来源: AIP

摘要:

An investigation has been carried out to determine the extensional mechanical behavior of a viscoelastic material when it is subject to an infinitesimal displacement field superposed on a finite steady deformation. Experiments were conducted on a thin strip of a polyester‐based polyurethane at a temperature of 77°F (±3°F). It is shown that the relaxation modulus of this material can be expressed as a product of two functions, one of which depends only upon the elongation ratio and the other only upon time. This form is applicable for basic‐state elongation ratios1⩽λ⩽1.2and for a period of 2 hr. It is noted that the separable form is highly suspect for longer time intervals.

ISSN:0148-6055    

DOI:10.1122/1.549159

出版商:The Society of Rheology    

年代:1969

数据来源: AIP

摘要:

This paper describes an experimental technique for determining visocelastic constants for molten polymers by tensile creep experiments. The constants determined were retardation times, shear compliances, zero‐shear flow viscosity, and shift factors. Data are given in terms of a generalized Voigt model. Polymers evaluated were several commercial polystyrenes. Experimental data indicate that the creep curves obtained at different temperatures do not exactly shift according to the time‐temperature superposition principle. A possible explanation of the discrepancy is proposed in the paper. Shift factors as obtained by creep experiments are compared with calculated values obtained by the WLF equation. Agreement is poor. However, the general expression of WLF type is applicable in correlating shift factors as a function of temperature. New sets of constants are obtained for polystyrene samples. Activation energy of polystyrene due to viscoelastic deformation is compared with the activation energy due to viscous flow deformation. For temperatures greater than 120 °C, the values obtained by the two types of deformation are equal, however, for temperatures lower than 120 °C, the activation energy due to viscoelastic deformation is much greater than viscous deformation. The activation energy obtained for viscoelastic deformation at lower temperatures agrees with values by retraction studies and birefringence measurements.

ISSN:0148-6055    

DOI:10.1122/1.549130

出版商:The Society of Rheology    

年代:1969

数据来源: AIP

摘要:

A series of tests is proposed to determine the possible 36 independent relaxation moduli of a homogeneous linear anisotropic viscoelastic body. The complete series comprises three simple shear tests, and 21 tests of a single type described as pure compression which employ essentially the same apparatus.

ISSN:0148-6055    

DOI:10.1122/1.549131

出版商:The Society of Rheology    

年代:1969

数据来源: AIP

摘要:

The expansion of a jet of viscoelastic fluid issuing from a capillary is measured. Two methods are suggested for estimating a relaxation time of the fluid. In one the dependence of the final jet diameter on residence time in the capillary is determined, and the calculated primary normal stress differences are interpreted through a model for the response of a Bogue fluid to the sudden imposition of simple shear. In the other, the shape of the extrudate is used to give an estimate of the normal stress difference as a function of distance from the capillary exit, and the data are interpreted through the solution for the stress decay in a Bogue fluid in steady shear, subject to a sudden cessation of shear. The resulting values of relaxation times as a function of shear rate are in good agreement for these two types of experiments, and agree well with values of the relaxation time based on the equilibrium normal stress difference as a function of shear rate.

ISSN:0148-6055    

DOI:10.1122/1.549132

出版商:The Society of Rheology    

年代:1969

数据来源: AIP

摘要:

Apparatus has been constructed to carry out precise measurements of rolling friction for rigid balls rolling over soft viscoelastic substrates, using a wide range of ball size, normal load, and rolling speed. Measurements are reported for two viscoelastic substrates, representing high and low energy loss elastomers. Measurements of the energy loss factor were also carried out for each substrate, using a simple rebound arrangement with a wide range of initial velocity and impact mass so that the contact time varied substantially. The rolling friction measurements were somewhat higher under all circumstances than the theoretical values, calculated using an energy loss factor appropriate to the contact time in rolling. The discrepancy at low rolling speeds was about the same magnitude as that reported previously by Greenwood, Minshall, and Tabor, and attributed by them to additional energy losses in complex strain cycles like those involved in rolling.

ISSN:0148-6055    

DOI:10.1122/1.549133

出版商:The Society of Rheology    

年代:1969

数据来源: AIP

摘要:

Vand’s modified equation has been extended to include the effect of three‐body collisions of spheres under shear. Brinkman’s equation has also been extended to derive an equation for the relative viscosity of concentrated suspensions of spheres by considering the dynamic formation of shear‐induced doublets and triplets of the suspended particles under shear. Vand’s estimation of the immobilized liquid during collisions has been critically examined and the equations derived have been modified on the assumption that only a fraction of Vand’s estimation is actually immobilized. Some deviations of experimental data from theory have been discussed and all the equations derived are compared with the data.

ISSN:0148-6055    

DOI:10.1122/1.549141

出版商:The Society of Rheology    

年代:1969

数据来源: AIP