Index of content:
Volume 20, Issue 1, March 1976
Linear and Nonlinear Viscoelastic Measurements, Ultimate Properties, and Processability of Raw Elastomers20(1976); http://dx.doi.org/10.1122/1.549401View Description Hide Description
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.
20(1976); http://dx.doi.org/10.1122/1.549428View Description Hide Description
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, and Deionized latices exhibited yield stresses which 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 viscosities at high shear rates were independent of electrolyte content. At intermediate electrolyte levels, variation of shear stress τ with shear rate γ̇ followed Casson's equation
Free Volume and Its Relationship to the Temperature Effect on Zero Shear Melt Viscosity: A New Correlation20(1976); http://dx.doi.org/10.1122/1.549403View Description Hide Description
20(1976); http://dx.doi.org/10.1122/1.549404View Description Hide Description
The flow of a viscoelasticfluid 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.
Linear Viscoelastic Response to a Deformation at Constant Rate: Derivation of Physical Properties of a Densely Crosslinked Elastomer20(1976); http://dx.doi.org/10.1122/1.549429View Description Hide Description
The stress‐time response, 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 modulus from the modulus that represents the linear viscoelastic response to the ramp function To illustrate the utility of obtained from only several tests, the stress‐time response to a strain rate of was measured on a densely crosslinked elastomer (an epoxy resin whose is 27°C) at 50, 60, and 90°C and at The data in conjunction with the WLF equation yielded: 1) the linear viscoelasticproperties, represented by either or over five decades of time; 2) the equilibrium (elastic)modulus; and 3) an acceptable value for 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 at to were converted into by a derived equation and found to agree with that obtained from 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.
20(1976); http://dx.doi.org/10.1122/1.549405View Description Hide Description
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.
20(1976); http://dx.doi.org/10.1122/1.549406View Description Hide Description
Relaxation of stress in simple extension of polyisobutylene (viscosity‐average molecular weight ) 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 coefficients and were obtained from two linear plotting procedures. At short times, decreased rapidly while remained essentially constant. Two to three logarithmic decades of time later, decreased. Thus, the terminal zone of viscoelastic behavior corresponds solely to the contribution. 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 of but lower values of
Comparison of the Dynamic Mechanical Properties of Two Styrene‐Butadiene‐Styrene Triblock Copolymers with 1,2‐ and 1,4‐Polybutadiene Center Blocks20(1976); http://dx.doi.org/10.1122/1.549407View Description Hide Description
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.
20(1976); http://dx.doi.org/10.1122/1.549408View Description Hide Description
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 adhesivefracture energy of the bond or to assess its mechanical integrity in pulsatile flow, providing an independent measurement of the energy has been made.