will exhibit a substantial reduction in fatigue life when exposed to a corrosive
environment. In some cases, the reduction is severe, in other cases it is less
dramatic, but only a very few materials show a fatigue resistance in a corrosive
environments as great as that in dry air.
Corrosion fatigue is the
reduced ability of a metal to withstand repeated stress when exposed to the
combined action of stress and a corrosive environment as compared to the effects
of stress alone.
Mechanism of Corrosion Fatigue.
Fatigue resistance can be reduced by corrosion activity in many ways. In
materials that are susceptible to stress corrosion, fatigue resistance is
probably lowered by the rapid propagation of fatigue cracks after they reach the
size required for stress corrosion cracking. In materials not susceptible to
stress corrosion cracking, corrosion probably enhances crack propagation
through direct attack at the crack tips, or by the formation of stress risers
such as pits.
Corrosion fatigue is usually 4-20 more severe at low cycling frequency where the
longer time to failure allows more corrosion activity to occur.
Examples of Corrosion Fatigue.
High strength steels are susceptible to substantial reduction in fatigue
resistance in many environments. The endurance limit (stress below which fatigue
failure will not occur) is often reduced by a factor of ten from that measured
Cathodic protection can increase the resistance of steels to corrosion
fatigue, but care must be taken not to overprotect them as
embrittlement would then occur. Titanium alloys, which are not subject to
corrosion cracking, are particularly resistant to corrosion fatigue as are some
of the more corrosion resistance
alloys, such as Inconel 625 and Inconel 718.
alloys and stainless steels are also susceptible to corrosion fatigue
with a reduction of one-half in their endurance limit being common.
Appearance of Corrosion Fatigue.
Corrosion fatigue gives a fracture surface similar to ordinary fatigue except
that in some cases, corrosion products are present in the outer sections of the
In the simplest corrosion fatigue test, the electrolyte is simply dripped over
the surface of a rotating beam fatigue test specimen. In more sophisticated
tests, flat specimens are stressed as cantilever beams and only tensile stresses
are induced on the surface exposed to the corrosive environment. When cyclic
loading is a factor in design, fatigue data from tests that include the
corrosive environment must be used.
Source : "Corrosion Control" NAVFAC MO-307
Corrosion Types of Corrosion Forms
What is Corrosion?