Solute-drag (SD) creep in Class I alloys is characterized by several features. Among these is the presence of “inverse” creep transients, which are unique to these solid-solution alloys and the SD creep mechanism. Creep transients in commercial AA5083 materials under SD creep are analyzed using a model based on a graphical construct previously proposed. It is observed that transient behavior can be represented in a general fashion which predicts the decay in relative transient size as a function of strain. Experimental data for SD creep are presented using the proposed graphical construct to determine the dependence of dislocation glide speed on stress and the dependence of equilibrium mobile dislocation density on stress. It is observed that the high stress exponents of the commercial AA5083 materials under SD creep, relative to low-impurity, binary Al–Mg materials, are primarily the result of an increased dependence of dislocation glide speed on stress.
Steady-state fluorescence measurements have been used to measure the rate of transport of a fluorescent probe (pyrene) out of ca. 200-340 nm thick films of poly(methyl methaerylate) (PMMA) in contact with supercritical CO2 at pressures in the range 34-76 bar (estimated CO2 content in the film from 0.06 to 0.17 weight fraction) and several temperatures (35, 50, and 65 degreesC). At constant temperature, the estimated pyrene diffusion coefficient increases by approximately 4 orders of magnitude from the lowest to the highest CO2 content (e.g., from ca. 5 x 10(-15) cm(2)/S for ca. 0.08 CO2 weight fraction to ca. 10(-1)0 cm(2)/s for ca. 0.17 CO2 weight fraction at 35degreesC). We compare the present results to our earlier study of CO2-swollen polystyrene (PS) and find: (1) For similar pressures Of CO2 at the same temperature, the enhancement of the pyrene diffusion coefficient is larger in PMMA than in PS, presumably as a consequence of the higher solubility Of CO2 in PMMA; and (2) at similar CO2 contents, the pyrene diffusion coefficient is higher in PS than in PMMA by several orders of magnitude, which we attribute to the PS higher free volume for pyrene diffusion compared to PMXIA for CO2-swollen films.