Why is the combination of pitting corrosion and oscillating stress a serious problem in a metal component?
Corrosion is the name given to a large set of chemical reactions whereby a pure metal is converted into a more stable oxide or hydroxide compound. The most commonly noticed form of electrochemical corrosion is the rusting of iron, which is responsible for the brown powdery material found on nails and iron sheets. Corrosion is associated with a considerable amount of damage to automobile parts, ships, railway lines, etc, and much research is being directed at techniques to mitigate the process.
Answer and Explanation: 1
Pitting corrosion is a type of wear of metal whereby the majority of the part is safe from corrosive attack except for a few locations where the corrosion-mitigating mechanism is not able to work. For example, if there is a crack in the paint applied on a metal, the entire intensity of the corrosive agent works at this weak point, causing the pit to grow very rapidly.
The presence of a deep pit on a piece of metal acts as a stress concentration point. All the load lines transferring stress have to concentrate around the pit, increasing the stress levels in the vicinity. The oscillating stress applied by the load causes fatigue failure at such a point much more rapidly than a monotonic load applied.
In short, the combination of corrosion pits and oscillating stresses greatly reduces the fatigue life of a piece of metal. Catastrophic failure may occur.
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fromChapter 20 / Lesson 6
Learn about corrosion. Understand the corrosion definition, what things or substances can be corroded, the factors that cause corrosion, and the ways to prevent it.