Volume 15, Issue 3, September 1971
Index of content:
15(1971); http://dx.doi.org/10.1122/1.549234View Description Hide Description
An experimental study was carried out on the phenomena of upper and lower yield points observed with hard, amorphouspolymersolids below the glass‐transition temperature. The effects of temperature, strain‐rate, specimen shape, working strains, and annealing on the appearance of the upper and lower yield points were examined on epoxy cast resin (a three‐dimensional cross‐linked polymer) and on Celluloid (a linear polymer). It has been concluded that upper and lower yield points represent transient behavior, at a given moderate strain‐rate, associated with mechanical heterogeneity, expressed as a distribution of relaxation times. Some applications of this yielding mechanism are discussed.
15(1971); http://dx.doi.org/10.1122/1.549235View Description Hide Description
When a dilute polymer solution is sheared between concentric cylinders with the inner cylinder rotating and the outer fixed, the onset of cellular secondary flows (Taylor vortices) is usually delayed relative to a Newtonian liquid of the same kinematicviscosity, and the extra torque in the polymer solution following instability is less than that for the Newtonian liquid at the same relative Taylor Number. This torque reduction is explained here by means of a finite amplitude analysis of the secondary motion in a second‐order fluid using the energy equilibrium approach of Landau and Stuart. The theoretical calculations are in general agreement with data of Denn and Roisman for a 0.5% solution of polyisobutylene in decalin. Using these calculations and the linearized stability theory it is possible to estimate the three rheological parameters for a second‐order fluid from a single set of torque‐rotational speed data in a Couette viscometer.
15(1971); http://dx.doi.org/10.1122/1.549224View Description Hide Description
The emphasis of this presentation is directed toward (1) indicating typically the current state‐of‐the‐art with regard to experimentally observed rheologic response characteristics of clay soils subjected to dynamic loadings, both with and without inertial effects, and (2) evaluating the applicability of linear viscoelastic theory to characterize this response. Primary concern is given to steady‐state vibratory and single pulse loadings, and the particular soil properties considered include dynamic modulus and compliance, strength, energy dissipation, viscosity,relaxation time, compaction, and wave propagation velocity and attenuation. In addition, a qualitative thermodynamic interpretation of the observed constitutive response is advanced. A special effort is made to illustrate the influence on soil behavior of several often overlooked factors, such as certain materialcharacteristics of the soil (nature of pore fluid, particle orientation and arrangement, method of preparing specimens, etc.) and type of testing conditions (specimen size and geometry, boundary conditions, etc.).
15(1971); http://dx.doi.org/10.1122/1.549225View Description Hide Description
An effort is made in this state‐of‐the‐art paper to present a representative sample of the experimentally observed rheologic response characteristics of cohesionless soils subjected to dynamic loadings, both with and without inertial effects, and to evaluate the usefulness of various idealized continuum and particulate theories for describing this response. Following brief discussion of some fundamental stress‐strain‐strength characteristics of cohesionless soils, their general behavior under dynamic loads is discussed. Then, their dynamic response is conveniently divided into two categories: reduction in volume and constitutive properties, and each is examined in some detail. The former includes conditions, such as compaction and liquefaction, which are associated with gross alterations in the soil structure; the latter is concerned with the stress‐strain relation, hysteretic response, and wave propagation characteristics of the soil throughout the range of deformation encountered. Particular emphasis is given to distinguishing between small‐strain and large‐strain response and the approximations which are acceptable for each case.
15(1971); http://dx.doi.org/10.1122/1.549226View Description Hide Description
It has been found that high‐resolution protonmagnetic resonancespectra can be obtained on swollen polymers and copolymers as well as plasticized polymers. In block copolymers of bisphenol‐A polycarbonate and polydimethyl siloxane of constant composition and molecular weight which have been swollen with deuterated cyclohexane, the mobility of the aromatic protons is dependent upon block length, while the mobility of the gem dimethyl and the siloxane methyl protons is not. This information will be discussed and used to interpret the morphology and properties of such copolymers.
15(1971); http://dx.doi.org/10.1122/1.549227View Description Hide Description
Measurements have been made of the apparent density of polymer melts extruding from a reservoir into a capillary orifice. The technique involves simultaneous measurement of extrudate mass and the corresponding decrease in volume of polymer in the reservoir. Data at low shear rates agree closely with density values from other experimental methods. Sequential density readings fluctuate because variations in speed of the driving piston are damped by successive compressions and expansions of the polymer melt. A linear polyethylene was shown to suffer a significant density decrease as the shear rate was increased. This dilation is due to the triaxial action of normal stresses and can be used, with an appropriate model, to estimate the primary normal stress difference and recoverable shear in the flowing melt.