Do You Know What Is Corrosion Fatigue?
Corrosion fatigue is said to occur when a metal mechanically degrades faster than expected under the combined action of cycling loading and corrosion. Just as its name suggests, it is simply defined as the fatigue experienced in a corrosive environment. Do you know that the most common cause of engineering failure is due to fatigue? And when corrosion is introduced, it makes matters worse because you are not guaranteed of a safe stress range.
What Causes Corrosion Fatigue?
Because of the joint action of corrosion and cyclic stress, the metal fractures and causes corrosion fatigue. Although not constant in all cases of corrosion fatigue, it can be said that the crack development is due to quick fluctuating stresses that are below the tensile strength. And when stress increases, the possibility of the fracture decreases.
The fatigue life accorded as a max stress value is also known as the fatigue strength. This fatigue strength will see a dip whenever a material is placed in an aggressive environment. To anticipate the possibility of corrosion fatigue, you have to look at environmental, loading, and metallurgical factors.
What Types of Metal Products can Corrosion Fatigue Occur in?
From small metal panels used in ship building to those used in manufacturing heavy industrial equipment, corrosion fatigue can happen in so many types of metal products. Basically, during a static loading, those materials that can repassivate are all considered to be vulnerable to repeated oxide film rupture. We can say that no metal is immune to a reduction in cyclic stressing resistance if you place that metal in a corrosive environment.
Stress Corrosion and Corrosion Fatigue are Not the Same Thing
Stress corrosion is crack initiation and crack development due to a sustained load or residual stress. This is different from corrosion fatigue and both entities should not be confused with one another. While corrosion fatigue features transgranular cracks, stress corrosion usually features intergranular cracks. In addition, corrosion fatigue can be prone to most materials (especially high strength alloys); stress corrosion is rarely seen in technical materials.
The Prevention of Corrosion Fatigue
As with most problems, there are always possible solutions. To prevent corrosion fatigue, what you need is through a reduction of different things, which include:
- Reduction of corrosion through the use of inhibitors and coatings to stall time before corrosion fatigue cracking starts
- Reduction of fatigue by controlling and bringing down the pressure and vibration fluctuations
- Reduction of corrosion through the use of high performance alloys which are resistant to corrosion fatigue
When you have understood what constitutes corrosion fatigue and the problems it can cause, you will also understand why fatigue tests are conducted in materials science. In a real-life example, by learning the crack growth characteristics of corrosion fatigue on marine and offshore structures, you will be able to design such structures more efficiently to prevent structure construction failures or collapses.