摘要:

In this paper the secondary creep stage of anisotropic solids in a state of multiaxial stress is considered. The theory is based on the assumption of the existence of a creep potential, which can depend only on invariants of the stress tensor or its deviator, if the material is isotropic. The anisotropic behavior is described by using a mapped stress tensor instead of the actual stress tensor in the isotropic creep potential. Assuming a linear transformation, the anisotropic behavior is expressed by a material tensor of rank four. The theory of the creep potential is based upon the principle of maximum dissipation rate, from which, following Lagrange's method in connection with a creep condition, one obtains the flow rule of anisotropic materials. This flow rule leads to the constitutive equations formulated in this paper. The material constants involved in these equations are related to experimental data. For example, the orthotropic case is considered, and the Poynting‐effect is accounted for. Furthermore, the influence of the “second‐order” effect and of the anisotropy on the creep‐behavior of a thin‐walled tube subjected to internal pressure is investigated.

ISSN:0148-6055    

DOI:10.1122/1.549631

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

Dye concentration measurements were carried out by withdrawing samples of dilute polymer solutions which were injected from tubes and slots in a large outside flow field. The colorimetric concentration measurements were found to be dependent on sampling rate. No effect of sampling rate was observed for aqueous dye‐only solutions or for homogeneous polymer solutions. The unexpected dependence of concentration measurements on sampling rate is apparently due to large elongational viscosities of the polymer solutions, which are functions of polymer concentration.

ISSN:0148-6055    

DOI:10.1122/1.549632

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

The rheological properties of concentrated solutions of nylon 6,6 of various molecular weights in various solvents have been determined in steady shear flow. Four solvents including 90% formic acid,m‐cresol, 97%H2SO4,and 100%H2SO4were selected based on their effect on the ionic nature of nylon 6,6 in dilute solutions. The magnitude of the rheological properties of concentrated solutions depended on the solvent when compared at the same shear rate(γ̇)and segment contact parameter (cM̄w,wherecis the concentration andM̄wis the weight average molecular weight). However, as observed by others, the critical value ofcM̄wfor the onset of entanglements was independent of the solvent. The contact parameter was effective in reducing values ofη0versuscM̄wto a single curve for three of the solvents but values ofη0for formic acid solutions were consistently two orders of magnitude lower than for the other solutions. Values of the equilibrium compliance,Je0,were highest for the formic acid solutions. However values of the reduced compliance(JeR)for all four solutions were around 0.4 which is in reasonable agreement with the Rouse theory. The onset of non‐Newtonian viscosity depended on the solvent but the shape of the flow curves was similar for all polymer/solvent systems. It is concluded that the solvent viscosity may contribute more to the rheological properties of concentrated solutions than the solvent's influence on the ionic nature of polymer chains.

ISSN:0148-6055    

DOI:10.1122/1.549633

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

Based on fundamental continuum mechanics, the analysis of the converging flow at the die entry, where extensional deformation predominates, leads to the following relations:σ22=2PE(d ln PE/d ln γ̇12),PE=P0−F(β)σ12.Hereσ22is the stress normal to the die wall at the exit, andσ12andγ̇12are the wall shear stress and shear rate at the die exit.PEandP0are the extensional pressure loss and the experimentally measured entrance pressure loss, respectively.F(β)is a shape factor which is determined from the converging die angle (β). Formulations ofF(β)for the conical and flat converging dies are developed. With Teflon‐coated and well lubricated converging die, the entry pressure drop is reduced in line with the predictions from this analysis. The derivation also leads to the definition of Weissenberg number in converging flow which is the ratioσ22/2σ12.It is related to the level of long‐chain branching and onset of melt fracture of polyethylene.

ISSN:0148-6055    

DOI:10.1122/1.549651

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

The literature on the rheology of liquid crystals formed from rod‐like molecules is reviewed in this article. After a brief introduction to liquid crystals in general and their rheology in particular, the types of polymers that form liquid crystal phases and the conditions for liquid crystal formation are summarized. The framework for the discussion of the rheology of polymeric liquid crystals is based on the three‐region flow curve proposed by Onogi and Asada. The plateau viscosity region is the one best understood, with general agreement among various studies and with theory. The data for onset of shear thinning at high shear rates and for other viscoelastic phenomena are not consistent among different investigators. Many liquid crystal polymers have an initial shear thinning region and appear to have a yield stress. Rheo‐optical data suggest that this is the result of the domain texture which commonly exists in liquid crystal systems. In many cases, this behavior is confounded by chemical effects such as aggregation or crystallization, which give rise to sample history effects and which probably account for some of the discrepancies in the literature.

ISSN:0148-6055    

DOI:10.1122/1.549634

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549652

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549635

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549653

出版商:The Society of Rheology    

年代:1981

数据来源: AIP