Corrosion Fatigue (new) [mechanical failure mode]
Corrosion Fatigue by definition is fatigue in a corrosive environment. An aggressive envronment can be harmful for the fatigue life of a structure, and protection against corrosion is necessary. Designers must consider corrosion in service, not only in view of fatigue. Corrosion is undesirable for reasons related to a safe and economic use of a structure during its service life. Corrosion can also be unacceptable in view of the apperance of a structure, i.e. for cosmic reasons. Usually, corrosion prevention is considered to be a matter of selecting a corrosion resistant material or applying a suitable surface protection, such as paint or cadmium plating, etc. Unfortunately, these operations do not guarantee good fatigue properties. Furthermore, several high-strenght materials have realatively poor corrosion resistance. Disastrous accidents have occured due to fatigue cracks starting from corrosion damage, in several cases corrosion pits. Whenever corrosion damage can occur to the material surface of a dynamically loaded structure, corrosion fatigue can be a serious problem.
(Fatigue of Structures and Materials Author: Jaap Schijve p.457)
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Blue Brittleness (old) -none
Blue Brittleness (new) [mechanical property]
This is a phenomenon that has been recognized in steels for many years. Its name is a result of the fact that it occurs in the temperature range(several hundred degrees centigrate above room temperature) where a "blue" oxide film is formed on the surface ot a steel specimen.
The term "blue brittleness" is somewhat of a minomer, as the metal does not become brittle in the normal sense. What actually happens is that the elongation in a tensile test undergoes a minimum at the blue brittle temperature. However, the reduction in the area of the tensile does not normally show a pronounced minimum at the blue brittle temperature. This signifies that the fracture is not brittle.
(Physical Metallurgy Principles Author: Reza Abbaschian,Lara Abbaschian,Robert E. Reed-Hill p.705)
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