Corrosion fatigue characteristics

Thermal fatigue characteristically results from temperature cycles in service. Even if an alloy is con ectly selected and operated within normal design limits for creep strength and hot-gas corrosion resistance, it can fail from thermal fatigue. 

Corrosion fatigue, resulting from the combined effects of corrosion and cyclic stresses. Racks of Ihis type are characteristically Iranscrystalline. 

It is important to recognize that all materials will have problems in certain environments, whether they are plastics, metals, aluminum, or something else. For example, the corrosion of metal surfaces has a damaging effect on both the static and dynamic strength properties of metals because it ultimately creates a reduced cross-section that can lead to eventual failure. The combined effect of corrosion and stress on strength characteristics is called stress corrosion. When the load is variable, the combination of corrosion and the varying stress is called corrosion fatigue. 

The Nonzero Minimum-Life Case. In many situations, no failures are observed during an initial period of time. For example, when testing engine bearings for fatigue life no failures are expected for a long initial period. Some corrosion processes also have this characteristic. In the foUowing it is assumed that the failure pattern can be reasonably weU approximated by an exponential distribution. 

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