The molecular‐weight dependence of the glass‐transition temperature (Tg) of a series of atactic polyacrylonitriles (PAN)s was studied by inverse gas chromatographic (IGC) analysis. PANs having different molecular weights were prepared by either; (i) the addition of isopropyl alcohol as a chain‐transfer agent, or (ii) a scission reaction induced by the addition of alkali (NaOH) to a solution (N,N‐dimethylformamide solution, at 25 °C) of the resulting polymer. The intrinsic viscosity [η] was in the range of 10.9–0.1 (dl · g−1), which corresponds to a viscosity‐averaged molecular weight (Mv) of 1 590 000–3 000. As part of the results, a side reaction, which saw the conversion of the nitrile (CN) groups of PAN into amide (CONH2) and/or carboxylic acids (COOH) groups by alkali, was found to occur. The typical molecular‐weight dependence of the Tg in free‐radically prepared PAN was discussed in connection with a chain‐transfer mechanism in an aqueous medium.Molecular‐weight dependence of the Tg for PAN (WA). An error bar is given by a short vertical arrow.magnified imageMolecular‐weight dependence of the Tg for PAN (WA). An error bar is given by a short vertical arrow.
The uniaxial version of the viscoplasticity theory based on overstress is applied to the deformation behavior of Type 304 stainless steel at 650°C. The effects of strain rate, waveform, and position of hold-time are computed for a cyclic steady-state as well as the ratchetting behavior under zero-to-tension load control.
The computations of deformation behavior are used in correlating and predicting the low-cycle fatigue life at 593°C using the strainrange partitioning method as well as an incremental damage accumulation law developed previously. The results of the computations exhibit the appropriate trends, but can show deviations from actual life exceeding a factor of two. Considering all the uncertainties, the results are deemed acceptable and promising.
The incremental damage accumulation law permits application to arbitrary stress or strain histories. The effect of position of hold-time on the hysteresis loop is computed and shown to exhibit the appropriate trend.
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