Corrosion fatigue loading frequency

Consequently, the parametric response of a material to corrosion fatigue loading may be quite complex, and the description of corrosion fatigue behavior must take into account not only the level of mechanical loading but also the load frequency and the shape of the cycles. Results should be expressed in terms of time related crack growth rate (dfl/dr) rather than the more frequently used cycle dependent crack growth rate (da/dn). 

Cyclic load frequency is the most important factor that influences corrosion fatigue for most material environment and stress intensity conditions. The dominance of frequency is related directly to the time dependence of the mass transport and chemical reaction steps involved for brittle cracking. 

Figure 9.16. Variation of cycle-dependent component of corrosion fatigue crack growth rate with inverse frequency (or loading period) for an AISI 4340 steel tested in water vapor (at 585 Pa) at room temperature [10].

Loading frequency and moderate variation of temperature have little effect upon the number of cycles to fracture in dry fatigue. These factors are more important in CF. The effect of frequency is significant because flie corrosion effect is time dependent, and the temperature is known to be an important factor in connection with corrosion. These two factors are mentioned at the same time because they both represent possible ways of accelerating CF tests. Reliable test results can, however, be obtained only if the fatigue acceleration factors are quantitatively known. 

Low cycle corrosion fatigue for strain-induced fatigue corrosion with low-frequency load cycles on materials and protective layers... 

FIG. 8—The varied effects of loading frequency on CF crack propagation rate in peak aged AA7075, 7017, 7475, and 7079 exposed to aqueous chloride eoiution (free corrosion) at constant AK and R. The fatigue crack is parallel to the plate rolling plane in the SCC sensitive S-L orientation [50]. 

Stress corrosion cracking and corrosion fatigue may have common features and there is a continuum of morphology and mechanisms between the two phenomena, CF becoming similar to SCC as the loading frequency is decreased. In the same way, the distinction between HE and SCC or CF is... 

The cyclic load frequency seriously affects corrosion fatigue. The service life of a component depends upon ... 

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