Volume 18, Issue 2, July 1974
Index of content:
18(1974); http://dx.doi.org/10.1122/1.549355View Description Hide Description
This paper provides a derivation of the axial stress distribution and the total thrust in the generalized torsional flow of Pipkin and Tanner. A new interpretation of the formula in the inverted‐cone technique of Cowsley to find the second normal stress difference is also given, along with the use of a shallow spherical shell to find the normal stress differences.
18(1974); http://dx.doi.org/10.1122/1.549356View Description Hide Description
The time‐dependent viscosity of bentonite‐water suspensions was studied experimentally in Couette flow for various transitions between constant shear rates. It was found that after a sudden change in the shear rate the time dependence of the viscosity can be described by with In general, the characteristic times: 1) become longer as the differences in shear rates become smaller; 2) decrease with increasing concentration; 3) show little temperature effect for a 20°C temperature change. A theory for the time‐dependent behavior is given which can reproduce the essential features of the experimental results.
18(1974); http://dx.doi.org/10.1122/1.549333View Description Hide Description
A new instrument has been developed which permits direct measurement of the stress distribution functions for cleavage (normal stress) and shear (tangential stress) mechanisms of boundary fracture in peeling of viscoelastic material. The design theory, construction, and operation of the instrument are reviewed in detail. The influence of peeling angle upon the cleavage and shear stress distributions is investigated and analyzed. The results show that the cleavage and shear stress distributions correlate with different time scales of rheological response as predicted by available viscoelastic theory of fracture in peeling.
18(1974); http://dx.doi.org/10.1122/1.549334View Description Hide Description
A theoretical and experimental investigation of the dynamic mechanical properties of polymeric films in liquid media has been conducted. In an analytical development the effect of a viscous medium surrounding the specimen on the dynamic mechanical measurement is determined by calculating the viscous drag on the specimen which is subjected to a sinusoidal oscillation; this result is incorporated with the dynamic modulus analysis. The resulting expressions are demonstrated to predict the effective dynamic mechanical properties of films in liquid media by knowing the dimensions, viscosity, and density of the liquid and the frequency of oscillation. In order to separate the viscous drag from any polymer‐solvent interactions, a series of experimental studies using the Vibron instrument was conducted to measure the effective dynamic mechanical properties of films in a variety of noninteracting liquid media and dry conditions. The resultant dry measurements were used along with the theory to show the effect of viscous drag on the dynamic mechanical properties of a film in a liquid medium.
18(1974); http://dx.doi.org/10.1122/1.549335View Description Hide Description
An experimental study of the kinematics of the gravity flow of granular materials through hoppers is presented. A radiographic technique was employed to determine simultaneously the velocity and porosity fields in a granular material flowing through a model hopper. It was found that the flow of granular materials through hoppers is characterized by regions of rigid body motion interspersed with narrow bands of drastic change in void ratio and velocity. A major conclusion of this study is that the kinematic assumptions employed in previous theoretical analyses of granular materials flowing through hoppers or in converging channels are not consistent with the salient kinematic phenomena observed. Knowledge of the kinematic phenomena detailed here is basic to the proper analysis and design of hoppers.
18(1974); http://dx.doi.org/10.1122/1.549336View Description Hide Description
Stress levels in elongational flow of suspensions of long fibers have been determined experimentally using a jet thrust apparatus. Stress levels for fibers with an axis ratio of 340 and a volume fraction of 0.001 exhibit stresses nearly an order of magnitude above values for a pure Newtonian fluid. A recent theory by Batchelor is shown to give the correct dependence of stress on axis ratio and concentration, but the predicted magnitude of stress is generally lower than the experimental values.
18(1974); http://dx.doi.org/10.1122/1.549337View Description Hide Description
Some new conceptions of the current condition of our planet emerge from analyses of the tidal motions of the earth which take into account the effect of scale on the mechanical behavior of materials. In particular, mechanisms for the production of earthquakes,volcanoes, and continental drift are suggested. The results are compatible with available data and suggest new observations and experiments which might be useful for earthquake prediction or for the discovery of geothermal energysources.
18(1974); http://dx.doi.org/10.1122/1.549362View Description Hide Description
Parallel and orthogonal superposed flow results have been obtained experimentally. It has been found that at large values of the frequency of oscillation, the dynamic viscosities and merge with the dynamic viscosity η′ for oscillatory shear alone and the storage moduli and become parallel to the storage modulus for oscillatory shear alone. Results are presented here showing that the conclusions by Bernstein, Huilgol, and Tanner that the K‐BKZ model correctly describes the high‐frequency asymptotic behavior are unwarranted and that, consequently, the predictive ability of the K‐BKZ theory for these flows remains unknown. The claim by Bernstein and Huilgol that the behavior of the Bird‐Carreau model is at variance with the experimental evidence is discussed and formal arguments are presented showing that the Bird‐Carreau and M‐OWFS model predictions do conform with the experimental data.
18(1974); http://dx.doi.org/10.1122/1.549338View Description Hide Description
Certain low‐frequency asymptotic relations originally derived from the K‐BKZ model for parallel and orthogonal superposed flow are evaluated with experimental data and in terms of the predictions of six additional models. For orthogonal superposed flow, Tanner and Williams show that the data are consistent with the asymptotic relation, and it is shown here that all six additional models also predict this relation. For parallel superposed flow, the author's data are in conflict with the K‐BKZ model relation, and it is shown that only three of the additional models correctly do not predict this relation. These models (the Bird‐Carrreau model, the WJFLMB model, and the generalized pearl‐necklace model of Booij) also are the only models not to predict the general relation between the complex moduli for parallel and orthogonal superposed flow derived for the K‐BKZ theory by Yamamoto and Takano and by Bernstein. Analysis shows that the low‐frequency asymptotic relations jointly can be considered a special case of the general relation, and that, therefore, it is expected that the general relation will be rejected when parallel and orthogonal superposed flow data become available for the same fluids.