Aging superposition

The aging superposition process can be combined with the TTSP provide more extensive information of the material response as a function of time, aging time and temperature. In the last two decades many have studied physical aging extensively. Representative references include Wong, et al., (1981), McKenna, (1989, 1994), and Crissman, et al., (1990). A discussion... 

Fig. 112 Comparison of the temperature dependence at 1 Hz of mechanical E" ( , ) and dielectric m" (thin and thick continuous lines) modulus of quenched and aged PMMA, respectively, after superposition of the low-temperature part of the /3 transition (from [75])...

Figure 6-5 Dynamic Moduli (DG, UG") as a Function of Frequency at 20°C, Measured at Different Aging Times ([low-methoxyl pectin] = 6.1 gL , [Ca +] = 2.4x 10 mol, pH7,0.1 mol NaCl). To avoid superposition of data, values A) shown were added to G. ...

Figure 4.16 Creep compliance (strain per unit imposed tensile stress) versus time for glassy polyvinylchloride after aging for various times after a quench from equilibrium at 90°C to a glassy state at 20°C. The master curve with many symbols is the superposition of all the curves and is obtained by a horizontal shift. The pluses were obtained by reheating to 90 C after 1000 days of aging, and then quenching again to 20°C, followed by one day of aging. This result shows that the aging process is thermoreversible. (From Struik 1976, with permission from the New York Academy of Sciences.)...

Most Australian playas have only a thin (centimetres to lm) surface halite crust that redissolves upon flooding and which reprecipitates by evaporation to dryness after flood-borne clastic deposition. By this mechanism the halite crust is preserved as the uppermost crust, with clastic sediment (up to 150 m thick) progressively accumulating beneath the halite crust (Figure 10.3A). This is an example where the strict relative age of superposition is challenged, at least with respect to the age of the solutes and salts. However, evaporite sediments commonly behave as their clastic equivalents. Hardie et al. (1978) and Smoot and Lowenstein (1991),... 

However, it was later discovered12 that, when aged, stretched fibers of sulfur were extracted with carbon disulfide, some of the reflections no longer appeared in the diffraction pattern. This result was explained13 on the basis that the original diffraction pattern was the superposition of two patterns, that of true fibrous sulfur, plus oriented crystals of one of the allotropes of S8. The earlier unit cell is thus clearly invalidated. 

Creep failure by accelerated aging with elevated temperature. The physical assumption in using this method is that the time-temperature superposition principle holds for the mechanical properties of the polymer over the time and temperature ranges of interest. 

In immiscible blends, the t-T principle does not hold. Eor immiscible amorphous blends it was postulated that two processes must be taken into account the t-T superposition, and the aging time [Maurer et al, 1985]. On the other hand, in immiscible blends, at the test temperature, the polymeric components are at different distance... 

Since there is a shift in the viscoelastic relaxation spectrum to longer times with aging time, aging can be followed using stress relaxation, creep or volume relaxation measurements. It has been shown that for aging experiments [Struik, 1978], momentary creep curves have a universal shape and a master curve can be constructed using either time-aging (t - y or time-temperature (t - T) superposition. 

Maurer et al. [1985] have examined the two-phase blend of acrylonitrile-butadiene-styrene copolymer, ABS, (Tg = 110°C) and polycarbonate of bisphe-nol-A, PC, (T = 151°C) using stress relaxation measurements. Four regimes of behavior were found. Below 70°C both (t - T) and (t - y superpositions were possible, because the aging rates p defined as ... 

Monte Carlo simulation results for the non-equilibrium and equilibrium d3oiamics of a glassy polymer melt are presented. When the melt is rapidly quenched into the supercooled state, it freezes on the time scale of the simulation in a non-equilibrium structure that ages physically in a fashion similar to experiments during subsequent relaxation. At moderately low temperatures these non-equilibrium effects can be removed completely. The structural relaxation of the resulting equilibrated supercooled melt is strongly stretched on all (polymeric) length scales and provides evidence for the time-temperature superposition property. 

Hgure 3 Time-tempoatiiie superposition of die diange in Active tmpoatuie versus log aging time data to a common a mptote in the glassy state. The rdieraioetempaatureis207.S C. Lines indicale the trends in the data... 

Time-aging time superposition was possible at all strains up to the yield strain and at all ternperamres smdied. The aging time shift rate, [t, was semi to vary systematically with both temperamre and strain. In the linear viscoelastic range, the shift rate remmned constant. At increasing strains the shift rate was seen to decrease, though this effect was less evident at higher ternperamres. The shift rate increased with increasing temperamre up to approximately 110 °C to 120 T, after which it rtqiidly decreased to zero at Tg. 

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