Fretting action

Mechanical effects Corrosion can often be initiated or intensified by the conjoint action of mechanical factors. Typical examples include the presence of inherent or applied stresses, fatigue, fretting or cavitation effects. Inhibitors that are effective in the absence of some or all of these phenomena may not be so in their presence. In fact it may not always be possible to use inhibitors successfully in these situations and other methods of corrosion prevention will be required. 

Majoul, I. (2004). Analysing the action of bacterial toxins in living cells with fluorescence resonance energy transfer (FRET). Int. J. Med. Microbiol. 293, 495-503. 

Evidently, fretting is worse in air than in an inert atmosphere.25 There is less damage in a humid atmosphere than in dry air since humidity can have a lubricant action, and the hydrated oxides are less hard than the dry oxides.25,90,93 Surfaces subjected to fretting wear have a characteristic appearance with red-brown patches on ferrous metals and adjacent areas that are highly polished because of the lapping quality of the hard iron oxide debris. 

The third possible mechanism results from the fretting action or small amplitude sliding between hammer and polymer induced as a result of vibrations in the impacting hammer. The surface temperature rise attributed to this effect may be estimated from (3) ... 

Any action in mitigating flow maldistribution must be preceded by an identification of possible reasons that may cause the performance deterioration and/or may affect mechanical characteristics of the heat exchanger. The possible reasons that affect the performance are [131,147] (1) deterioration in the heat exchanger effectiveness and pressure drop characteristics, (2) fluid freezing, as in viscous flow coolers, (3) fluid deterioration, (4) enhanced fouling, and (5) mechanical and tube vibration problems (flow-induced vibrations as a consequence of flow instabilities, wear, fretting, erosion, corrosion, and mechanical failure). 

FYom the multitude of intricate corrosion processes in the presence of mechanical action (friction, erosion, vibration, cavitation, fretting and so on) it is justified to touch upon corrosion types joined under a single failure mode induced by mechanical stresses. These are the stresses that govern the corrosion wear rate of metals during friction. Such processes are usually called corrosion stress-induced cracking in the case that the mechanical action is effective only in one definite direction, or otherwise termed corrosion fatigue in the case that compressive and tensile stresses alternate within cycles. In spite of the differences between the appearance of these corrosion types, they have much in common, e.g. fundamental mechanisms, the causes, and they overlap to a certain degree [19]. 

Mechanically assisted degradation can consist of the following types of corrosion erosion-corrosion, water drop impingement corrosion, cavitation erosion, erosive and corrosive wear, fretting corrosion, and corrosion fatigue (CF) (Fig. 1.14). Erosion-corrosion consists of the corrosion process enhanced by erosion or wear. Fretting corrosion consists of the wear process enhanced by corrosion. CF consists of the combined action of fluctuating or cyclic stress and a corrosive environment. 

Figure 8.21. Idealized model of fretting action at a metaiiic surface.

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