Corrosion fatigue occurs in metals as a result of the combined action of a cyclic stress and a corrosive environment. Corrosion fatigue is dependent on the interactions among loading, environmental, and metallurgical factors. For a given material, the fatigue strength generally decreases in the presence of an aggressive environment. The effect varies widely, depending primarily on the particular metal-environment combination. The environment may affect the probability of fatigue crack initiation, the fatigue crack growth rate, or both.

Corrosion Fatigue Crack Initiation:
Influence of environment on fatigue crack initiation of a material is illustrated in S-N curves(Stress vs Log of number of stress cycles to failure), which compare the smooth-specimen stresslife obtained from inert and aggressive environments. Because as much as 95% of the structure life is spent in crack initiation, S-N curve comparison provides a good indication of the effect of environment on crack initiation.

Corrosion Fatigue Crack Propagation:
Although the phenomena for corrosion fatigue are diverse, several factors are known to influence crack growth rate:

• Stress intensity range - In embrittling environments, crack growth rate generally increases with increasing stress intensity (DK);
• Load frequency - Cyclic load frequency is the most important variable that influences corrosion fatigue for most materials. The rate of brittle cracking above that produced in vacuum generally decreases with increasing frequency. Frequencies exist above which corrosion fatigue is eliminated.
• Stress ratio - Rates of corrosion fatigue crack propagation are typically increased by increase in the stress ratio. However, stress ratio has only a slight influence on fatigue crack growth rates in benign environments.
• Aqueous environment electrode potential - Strongly influences corrosion fatigue in aqueous environments. Controlled changes in the potential can result in either the complete elimination or the dramatic increase in brittle fracture cracking.
• Environment - Increasing the chemical activity of the environment decreases the resistance of the material to corrosion fatigue.

Effect of variables such as metallurgy, temperature, load history and waveform, stress state, and environment composition are unique to specific materials and environments.