Alternating stress conditions

Choices of alternative materials. Corrosion probes are carefully chosen to be as close as possible to the alloy composition, heat treatment, and stress condition of the material that is being monitored. Care must be taken to ensure that the environment at the probe matches the service environment. Choices of other alloys or heat treatments and other conditions must be made by comparison. Laboratory testing or coupon testing in the process stream can be used to examine alternatives to the current material, but the probes and the monitors can only provide information about the conditions which are present during the test exposure and cannot extrapolate beyond those conditions. 

Fatigue failure of metal under conditions of repeated alternating stress. 

Because of the symmetry of the monomer, it might be expected that the materials would be quite crystalline like linear PE. Although PIB crystallizes under stress conditions, but it does not crystallize under nonstressed conditions. This is because the geminal dimethyl groups on alternating carbons in the backbone cause the bond angles to be distorted from about the usual... 

Polymers which arc not cross-linked to form infinite networks can behave elastically under transient stressing conditions. They cannot sustain prolonged loads, however, because the molecules can flow past each other to relieve the stress, and the shape of the article will be deformed by this creep process. [Alternatives to cross-linking are mentioned on pages 20 and. 315.]... 

The dynamic viscosity r](cai) is conveniently defined under alternating shear-stress conditions. Assuming the fluid velocity along x and the velocity gradient along z, the solvent velocity at the position of the hth atom in the absence of the chain is... 

The model in Figure 5 includes formation of both soluble and insoluble complexes of sHsp and substrate. The formation of insoluble sHsp/substrate complexes is consistent with the in vivo transition of sHsps to an insoluble, structure-bound form under many stress conditions as discussed above. At present we can provide only speculative explanations for this insolubility in the context of the chaperone model of sHsp function. From in vitro studies, it is clear that the ability of sHsps to keep substrates soluble is dependent on the sHsp-to-substrate ratio, the rate of substrate denaturation, and other factors in vitro conditions can be manipulated to cause precipitation of sHsp and substrate, as well as to maintain substrate solubility. Thus, insolubilization could result from a type of overload of the soluble binding capacity of the sHsps. Since in vivo there is good evidence that the insolubilization is reversible, this leads to the intriguing question of the mechanism of resolubilization, and whether this is also a function of Hsp70 systems, or if additional components are required. Alternatively, sHsp insolubilization in vivo could result from interaction with insoluble components in the cell. 

Fig. 4.70 Fatigue curves of acrylonitrile-butadiene-styrene using regular specimens, specimens with holes (0 3 mm) as stress concentrator and dynamic weldline under alternating load conditions cTdai [O60ss].

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