Factors that influence fatigue strength of a component

Fatigue strength of metal components determined by:

Grain Size

When a material has a 'coarse grain' it has 'poorer' fatigue resistance than when it has a fine grain.

Component Shape

A fatigue crack often starts some point of stress concentration and so stress rising features such as an abrupt change of section e.g. sharp corners, keyways, etc., should be avoided if possible.

Surface Finish

Tooling marks act as stress raisers and so the fatigue resistance of a component can be improved by polishing etc.

Residual Stresses

Stressed produced by the machining operations will affect the fatigue resistance of a component. Tensile Stresses 'reduce' the resistance. Compressive Stresses 'improve' the resistance.

Corrosion

Corrosion produces a pitted surface and so introduces stress raisers. The fatigue strength of a component is reduced very considerably by corrosion.

Temperature

At high-temperature materials tend to lose their strength and also suffer 'grain growth' and so fatigue strength falls when the temperature is high.

Creep

The term 'Creep' is used to describe the 'slow plastic deformation' that occurs under prolonged loading, usually at high temperatures.