In this work, the porous media flow of polymer solutions of poly(ethylene oxide) (PEO), hydrolyzed polyacrylamide (HPAA), and their blends is investigated. Aqueous solutions of PEO exhibit critical extension thickening when flowing through porous media. HPAA solutions also exhibit critical extension thickening in excess salt environments, but their behavior changes to a more gradual extension thickening when dissolved in deionized water. The mixtures of solutions of HPAA and PEO therefore vary its porous media flow behavior, depending on the ionic environment. In deionized water, a critical extension thickening similar to that obtained with PEO is still observed when HPAA is mixed in at concentrations low enough so that its apparent viscosity does not mask the influence of PEO. In the presence of salt, only a critical extension thickening is observed, which is attributed to transient network formation of both PEO and HPAA molecules. The mixtures generally exhibit a less critical behavior and display a lower than expected sensitivity of the onset Reynolds number for extension thickening with concentration. The results presented herein indicate that interspecies molecular interactions through transient network formation and the associated flow modification play a major role in determining the complex non-Newtonian flow behavior of these polymer solutions.

The temperature and concentration dependences of the yield-stress are determined in the Cu/Zn system with polycrystalline brasses (0.03 to I .O at '10 Zn) and high-purity copper of the same grain size between 15 and 300 K. The data, as well as similar ones on other dilute copper alloys, given in the literature, are found to be well accounted for by the 'kink-pair-formation' model of solid-solution hardening, originally developed for concentrated solid solutions. At temperatures at which diffusional forms of recovery are absent, the model is shown to be applicable at all concentrations, with possiblc exceptions at levels below about 10-2%, and allows for the influence of work-hardening due to dislocations, present in the metal also in its solute-free 'ground state', on the process of solid-solution hardening. The kink-pair nucleation process is examined in dctail.Die Temperatur-und Konzentrationsabhangigkeiten der FlieMspannung wird im System Cu/Zn an Messing-Einkristallen 0,03 bis 1,0 At% Zn) und hochreinem Kupfer der gleichen KorngroDc im Bereich 15 bis 300 K bestimmt. Die Messungen, sowie gleichartige aus der Literatur entnommene Angaben iiber andere schwach legierte, auf Kupfer basierende feste Losungen, weisen auf die gute Anwcndbarkeit des Begriffes der Erzeugung von Kinkenpaaren, der friiher zur Erklarung der durch Legierung bedingten Verfestigung in konzentrierten festcn Losungen vorgeschlagen wurde, auch auf den Fall schwach legierter Metalle hin. Fur Temperaturen, bei denen keine diffusionsbedingte Erholung stattfindet zeigt sich das Modell bei allen Konzentrationen anwendbar; mogliche Ausnahmen diirftc man unter einem Niveau von ungefahr 10-20h erwarten. Die durch die Anwesenheit von Versetzungen bedingte mechanische Verfestigung, welche auch im legierungsfreien "Grundzustand" des Metalls vorhanden ist, wird im Modell beriicksichtigt. Einzelheiten des Kinkcnpaarbildungsprozesses werden erortert.

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The dependences of the logarithmic stress‐relaxation rate s ≡ − dσ/d 1n(1 + t/t0) of coarse‐grained high‐purity copper and brasses (c = 0.03 to 1.0 at% Zn) on the initial level of the compressive stress, σ0, and on temperature are determined, following incremental pre‐strains of ½ to 1% in the near‐linear work‐hardening stage, at total strains of 2 to 5%. The results are correctly encompassed by the relation s ˜ σ0T(T + Td)−1, representing a stochastic process of “slip nucleation and dynamic glide”, the latter occurring by percolation of dislocations through accessible zones of the glide planes. T outside the bracket refers to the temperature dependence of the nucleation rate, and (T + Td)−1 to the post‐nucleation slip distance. Its length is assumed to be limited by the frictional resistance to the movement of the dislocations, due to phonon scattering (T inside the bracket), and that arising from forest dislocations, solute atoms, etc. (Td). The theory facilitates derivation of the hitherto empirical “stress‐concentration factor” used in descriptions of the low‐temperature flow‐stress anomaly, which is manifest also in the present materials, and provides a clear indication of its origin.

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