Static fatigue describes how prolonged and constant

cyclic stress Cyclic stress is the distribution of forces (aka stresses) that change over time in a repetitive fashion. As an example, consider one of the large wheels used to drive an aerial lift such as a ski lift. The wire cable wrapped around the wheel exert ...

weakens a material until it breaks apart, which is called failure. It is sometimes called "delayed fracture". This damage happens at a smaller stress level than the stress level needed to create a normal

tensile In physics, tension is described as the pulling force transmitted axially by the means of a string, a rope, chain, or similar object, or by each end of a rod, truss member, or similar three-dimensional object; tension might also be described as t ...

fracture. Static fatigue can involve plastic deformation or crack growth. For example, repeated stress can create small cracks that grow and eventually break apart plastic, glass, and ceramic materials. The material reaches failure faster by increasing

. Static fatigue varies with material type and environmental factors such as moisture presence and temperature.

Applications

Static fatigue tests can estimate a material’s lifetime and hardness to different environments. However, measuring a static fatigue limit takes a long time, and it is hard to measure a material’s true static fatigue limit with full certainty.

Typical occurrence

Stress corrosion cracking

Stress corrosion cracking Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It can lead to unexpected and sudden failure of normally ductile metal alloys subjected to a tensile stress, especially at elevated temperature. SCC ...

(SCC) happens when a stressed material is in a corrosive (chemically destructive) environment. One example of SSC embrittlement is when moisture increases static fatigue effects in glass. SCC is also seen in hydrogen embrittlement, embrittlement of some polymers, and more.

Plastic Deformation (Plastic Flow)

Plastic deformation happens when stresses flatten, bend, or twist a material until it no longer returns to its original shape. This can create several cracks in the material and decrease its lifetime.

Examples of Static Fatigue and Stresses on Materials

Plastic pipes under water or other fluids experience hydrodynamic forces resulting in fatigue. The pipes reach failure sooner with higher temperature or increased exposure to aggressive substances. For static fatigue tests, rotating machines apply weight on the material under study causing it to bend in different directions, which weakens the material overtime.

References

{{Reflist Continuum mechanics Corrosion Deformation (mechanics) Fracture mechanics Materials degradation