摘要:

For a given piece of raw elastomer the laboratory measurements that must be made in order to determine its processability and the minimum effort required for a thorough characterization of the material behavior over the temperature, time‐scale, and deformation range of practical interest are discussed. Interconversion of time or temperature dependence of materials at small deformations or conversions of one type of measurement to another in the linear region of viscoelastic behavior have been well documented. However, these schemes have not been useful in analysis of processability where materials undergo large deformations well into the nonlinear region. This study demonstrates the applicability of a new strain‐time correspondence principle by which measurements at either small or large deformations may be calculated from each other. Also considered is how ultimate properties affect processability. This question is illustrated using milling as an example and by contrasting the behavior of elastomers on the mill to the failure envelope expressed as a modulus‐strain curve at failure. Further, the failure envelope is represented by a simple equation. The nondestructive part of the visoelastic behavior may be represented by a master curve which includes variation of temperature, time, and magnitude of deformation. The intercepts between the master curve and failure envelope define the ultimate properties.

ISSN:0148-6055    

DOI:10.1122/1.549401

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

Osmotically driven flow in a narrow, long channel whose walls are a rigid, ideal semipermeable membrane leads to a convective velocity field satisfying Burger's equation. A particular boundary value problem is solved exactly.

ISSN:0148-6055    

DOI:10.1122/1.549402

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

Free electrolyte was removed by ion exchange from monodisperse polystyrene latex. Non‐Newtonian viscosities were measured at volume fractions from 0.05 to 0.50, at various electrolyte concentrations. Electrolytes included HCl,K2SO4,MgSO4,Al2(SO)4)3,andTh(NO3)4.Deionized latices exhibited yield stressesτ0which decreased with the diminishing volume fraction and with increasing electrolyte concentration. The effect of added electrolyte upon the viscosity of a freshly mixed dispersion depended upon its equivalent concentration (normality) and was independent of the chemical nature or valence types of the ions. Limiting viscositiesη1at high shear rates were independent of electrolyte content. At intermediate electrolyte levels, variation of shear stress τ with shear rate γ̇ followed Casson's equationτ1/2=τ01/2+η11/2γ̇1/2.

ISSN:0148-6055    

DOI:10.1122/1.549428

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

ISSN:0148-6055    

DOI:10.1122/1.549403

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

The flow of a viscoelastic fluid in the annular region between two infinite, eccentrically‐mounted, rotating cylinders is analyzed. The flow is assumed to be sufficiently slow, so that the second‐order Rivlin‐Ericksen constitutive equation is applicable and so that inertial effects may be neglected. The resultant forces on the cylinders, as well as the distribution of their normal and tangential components, are calculated. No restrictions are placed on the ratio of the radii or on the distance between the cylinder axes.

ISSN:0148-6055    

DOI:10.1122/1.549404

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

The stress‐time response,σ(t),to a constant rate of strain, ε̇, followed by a constant strain is discussed. The Boltzmann superposition principle is used to obtain the stress‐relaxation modulusE(t)from the modulusF(t)≡σ(t)/ε(t)that represents the linear viscoelastic response to the ramp functionε(t)=ε̇t.To illustrate the utility ofF(t)obtained from only several tests, the stress‐time response to a strain rate of0.25 min−1was measured on a densely crosslinked elastomer (an epoxy resin whoseT0is 27°C) at 50, 60, and 90°C and atε⩽0.10.The data in conjunction with the WLF equation yielded:1) the linear viscoelastic properties, represented by eitherF(t)orE(t)over five decades of time;2) the equilibrium (elastic) modulus; and3) an acceptable value forT0.To show that the experimental results in fact represent linear viscoelastic behavior, stress‐relaxation data measured at 50°C immediately after a specimen had been stretched atε̇=0.25 min−1toε=0.10were converted intoE(t)by a derived equation and found to agree with that obtained fromF(t).The data along with results from ancillary tests at 10, 20, and 30°C gave the isochronous modulus F(0.015 min) over the rubber‐to‐glass dispersion zone.

ISSN:0148-6055    

DOI:10.1122/1.549429

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

The theoretical and experimental existence of transient strain responses which result from nonlinear interactions between loads applied at different times to viscoelastic materials with fading memory is demonstrated. A theory which retains the simplicity of a single‐integral model and yet which is capable of modeling transient strain responses is proposed. The theory is used to analyze some previously published data on poly(vinyl chloride), poly‐(methyl methacrylate), polyethylene, and polyurethane.

ISSN:0148-6055    

DOI:10.1122/1.549405

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

Relaxation of stress in simple extension of polyisobutylene (viscosity‐average molecular weight2.3×106) has been measured at stretch ratios (λ) up to about 2. Data at 3, 25, and 50°C were reduced to 25°C. At any instant of reduced time, the dependence of stress on λ could be described by the Mooney‐Rivlin equation; the coefficientsC1andC2were obtained from two linear plotting procedures. At short times,C1decreased rapidly whileC2remained essentially constant. Two to three logarithmic decades of time later,C2decreased. Thus, the terminal zone of viscoelastic behavior corresponds solely to theC2contribution. This result confirms measurements by Arai and Niinomi (Kogyo Kagaku Zasshi,74, 2525 (1971)) on polyisoprene and styrene‐butadiene rubber and measurements by Noordermeer and Ferry (J. Polym. Sci., (1976), in press) on 1,2‐polybutadiene. Tentative interpretations in terms of motions of entanglements are discussed. Similar measurements on a sample of polyisobutylene which had been heated with vulcanizing ingredients and was very slightly crosslinked gave higher values ofC2but lower values ofC1.

ISSN:0148-6055    

DOI:10.1122/1.549406

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

The dynamic mechanical properties of a polystyrene‐1,2‐polybutadiene‐polystyrene (SBS) triblock copolymer were studied in free oscillation experiments near 0.2 Hz from −50 to 100°C and in forced oscillations over a frequency range from 0.1 to 1000 Hz at various temperatures between 1 and 96°C. For data which covered essentially the polybutadiene transition region, the temperature dependence of the mechanical properties could be described by a WLF equation whose parameters are in close agreement with those describing homopolybutadiene of similar microstructure. Data outside the polybutadiene transition region showed considerable lack of superposition when reduced by the WLF equation, as observed earlier in a triblock of similar molecular architecture but having a 1,4‐polybutadiene center segment. Contour plots of the loss compliance as a function of the temperature and the logarithmic frequency revealed significant differences in the temperature and frequency dependence of various viscoelastic mechanisms responsible for the thermorheological complexity seen in both materials.

ISSN:0148-6055    

DOI:10.1122/1.549407

出版商:The Society of Rheology    

年代:1976

数据来源: AIP

摘要:

This study presents a continuum analysis of a simple pressurized cylindrical shell geometry relating to a problem of potential interest in biomedical engineering. Repair or partial replacement of veins by adhesive splicing rather than suturing involves an evaluation of the strength of the joint, especially at the ends where the prosthesis slips over or into the natural vein. Furthermore, the quality of the adhesive bond may change with biodegradability of the joint. The analysis suggested may be used either to deduce the specific adhesive fracture energy(γa)of the bond or to assess its mechanical integrity in pulsatile flow, providing an independent measurement of the energy(γa)has been made.

ISSN:0148-6055    

DOI:10.1122/1.549408

出版商:The Society of Rheology    

年代:1976

数据来源: AIP