What causes surface fatigue?

Surface fatigue is a common problem with gears. When gears with rough edges and insufficient lubrication come together repeatedly, they produce a cyclical stress. This cyclical stress can create discontinuities on the surfaces of the gear.

What are the three stages of fatigue failure?

There are three stages of fatigue failure: initiation, propagation, and final fracture.

What causes rolling contact fatigue?

The rolling contact fatigue phenomenon occurs in railways, gears, bearings, and other mechanical components involving rolling/sliding contact. RCF is caused by cyclic loading of the material and results in early fatigue damage called crack-like flaws.

What causes structural fatigue?

Structural fatigue, often originates in cracking in critical areas [2–4], is caused by the dynamic loads that are exerted by various effects with varying importance depending on machines element or structural component type.

What is surface fatigue?

Surface fatigue is the failure on the top layer of a body due to repeated loading. It can be differentiated from other types as it only occurs on the surface. It appears mainly in the form of microcracks and can propagate to other parts of the body, if left unchecked.

How do you prevent surface fatigue?

Selecting the right viscosity is key in reducing micropitting and surface fatigue. Higher loads will require higher viscosity, while lower loads allow for lower viscosities. Speed can also have an effect on micropitting and surface fatigue. At lower speeds, the film thickness will decrease.

What factors affect fatigue?

Fatigue life is affected by cyclic stresses, residual stresses, material properties, internal defects, grain size, temperature, design geometry, surface quality, oxidation, corrosion, etc.

How do I know if I have fatigue failure?

Fatigue failure is identified as starting at a stress raiser or defect, then the crack generates through the material before causing sudden failure. The crack progress is shown as smooth, rippled formation known as striations or beach marks, whilst the sudden failure is a classic brittle fracture with rough appearance.

What is Hertzian fatigue?

Hertzian Fatigue (Spalling) Spalling occurs when macropits form, then grow is size and coalesce into larger cavities on the gear tooth surface. Asperities and high pressures from variations in manufacturing tolerances. This form of macropitting quickly stops once the load redistributes.

What is shelling defect?

Shelling is an internal defect which generally initiates at a depth of 2-8 mm below the gauge corner of the high rails in curved track.

What causes fatigue in aircraft?

Possible causes of fatigue include sleep loss, extended time awake, circadian phase irregularities and work load. Despite regulations limiting flight time and enabling optimal rostering, fatigue cannot be prevented completely.

What causes fatigue in engineering materials?

Fatigue is defined as a process of progressive localized plastic deformation occurring in a material subjected to cyclic stresses and strains at high stress concentration locations that may culminate in cracks or complete fracture after a sufficient number of fluctuations.