The effects of couple stresses in fluids are considered. Linearized constitutive equations are proposed for force and couple stresses. A series of boundary-value problems are solved to indicate the effects of couple stresses as well as for experiments measuring the various material constants. It is found that a size effect comes in which is not present in the nonpolar case (couple stresses absent).

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Joining of plastics and plastic composites is becoming important because of the emerging structural applications of these materials. While providing an overview of all joining methods, this paper emphasizes the welding of thermoplastic materials. Different welding techniques, together with their main advantages and disadvantages, are briefly described. A selective bibliography, in which the 259 references have been arranged chronologically for each technology type, provides a guide to the literature.

In vibration welding of thermoplastics, frictional work done by vibrating two parts under pressure, along their common interface, is used to generate heat to effect a weld. The main process parameters in vibration welding are the weld frequency, the amplitude of the vibratory motion, the weld pressure, and the weld time. How these parameters affect weld quality, the conditions that result in the best welds, the weldability of dissimilar plastics, and the effect of fillers such as glass are of interest. To address these issues, a research vibration welding machine in which all the parameters can be independently and accurately controlled and monitored was designed and fabricated. The phenomenology of welding, a s determined by experiments on the four thermoplastics polycarbonate, poly (butylene terephthalate), polyetherimide, and modified poly (phenylene oxide), is described.

The analysis and experiments in this paper are restricted to the flow between two coaxial, infinite disks, one rotating and one stationary. The results of numerical calculations show that many solutions can exist for a given Reynolds number Ωl2/v (Ω is the angular velocity of the rotating disk and I is the spacing between the two disks). Out of a greater number of possible solutions, three solution branches have been identified; the branches correspond to one-, two- and three-flow cells in the meridional plane.The one-cell branch has been accorded detailed treatment. Within this branch there are two subbranches. The first, now well documented in the literature, includes solutions from zero to infinite Reynolds number. The latter limiting case is characterized by an inward-flowing boundary layer on the stationary disk and an outward-flowing boundary layer on the rotating disk. In between is a core flow rotating with a constant angular velocity. The second sub-branch of the single-cell flows, apparently unknown heretofore, begins with an infinite Reynolds number, decreases to a minimum and then increases to an infinite Reynolds number again. The first infinite Reynolds number limit again corresponds to two boundary-layer flows separated by a core flow with constantangular velocity opposite in direction to the angular velocity of the rotating disk. The second limiting case of infinite Reynolds number is the free-disk solution of von Kármán (1921). Asymptotic solutions have been obtained which more fully describe the nature of this flow as the Reynolds number increases.The second part of the paper presents experimental measurements corresponding to the Reynolds number range 0–100. Profiles were measured with a hot-wire anemometer. The measurements are in agreement with the first, one-cell branch of solutions. A semi-quantitative evaluation of edge effects is obtained.