Cyclic stress

Stress factors Sustained stress, cyclic stress, compression set (in rubbers) under continuous loading... 

Shimizu, T., Tsuda, A., Yokoo, H., Mizoguchi, K., Gondoh, Y., Matsuguchi, N. Tanaka, M. (1990). Effects of stress, non-stress cyclicity on hypothalamic noradrenaline release in rats. KurumeMed. J., 37,49-53. 

Characterization of modified electrodes can be carried out by electrochemical, spectroscopic, and microscopic methods. Of the electrochemical methods we stress cyclic voltammetry, chronocoulometry, and impedance, which combined together measure the number of redox centres, film conductivity, kinetics of the electrode processes, etc. Almost all the non-electrochemical techniques described in Chapter 12 have been employed for the characterization of modified electrodes. 

Environmental aging is usually less severe in service (laboratory tests tend to accelerate aging so that the testing can be completed in a reasonable time). However, the effects of the actual service environment are generally more complex. For example, there may be simultaneous exposure to cyclic stress, cyclic temperature, and humid environments. 

Pressure vessels are also subject to cyclic stress. Cyclic stress arises from pressure and/or temperature cycles on the metal. Cyclic stress can lead to fatigue failure. Fatigue failure, discussed in more detail in Module 5, can be initiated by microscopic cracks and notches and even by grinding and machining marks on the surface. The same (or similar) defects also favor brittle fracture. 

Thermal stress ratcheting is progressive incremental inelastic deformation or strain that occurs in a component that is subjected to variations of mechanical and thermal stress. Cyclic strain accumulation ultimately can lead to incremental collapse. Thermal stress ratcheting is the result of a sustained load and a cyclically applied temperature distribution. 

The stress below which a material can be stressed cyclically for an infinite number of times without failure. See S-N diagram. ... 

Annulus Fibrosis With its concentric laminated bands arranged in a helicoid manner, this structure functions as a universal joint between the fifth lumbar vertebra and the sacrum. Before degeneration of the disc occurred, it was able to resist the forces. When mechanical failure of a disc occurs due to sheer stress, torsional stress, cyclical loading and progressive slippage may occur. 

The fatigue limit is the stress below which a material can be stressed cyclically for an infinite number of times without failure. The fatigue strength is the cyclic stress a material can withstand for a given number of cycles before failure. The S-N diagram is the plot of stress (S) against the number of cycles (N) required to cause failure of similar specimens in a fatigue test of exactly the same conditions. 

The transition from thermal to mechanical failnre has been described in terms of a changeover stress level, which depends on test frequency, mean stress, cyclic waveform, and specimen surface area-to-volume ratio (24). An empirical relationship between the imiaxial changeover stress and test freqnency is shown in Figure 6 (24) and is given by... 

Hysteresis. The degree of lag in the reaction of a material to a change in the conditions (of mechanical, electrical, or magnetic stress) to which it is exposed. Ceramic ferro-electrics, for example, exhibit hysteresis when subjected to a changing external electric field hysteresis is also shown by plastic clay when it is stressed cyclically. 

An electron transfer mechanism is advanced for various classes of anticancer agents. The neoplasm is presumably destroyed by induction of oxidative stress. Cyclic voltammetry was performed on some of the main categories quinones (3-methoxy-o-benzoquinone, etoposide model), metal complexes [Cu(II)(3,5-diisopropylsalicylate)2] (Cu Dips) and iminium from bis(9-aminoacridines). Reduction potentials ranged from +0.28 to -0.88 V. Electrochemical behavior is related to structure and physiological activity. 

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