What is fatigue in materials science?

Fatigue is the progressive weakening of materials through the initiation and propagation of cracks caused by repeatedly applied cyclic loads. Although historically associated mostly with metal components like railway axles, most materials including plastics, composites, and ceramics experience fatigue-related failure. Damage often begins at stress concentrations when loads are well below the material's yield strength.

What we know

• Fatigue involves the initiation and propagation of cracks in a material due to cyclic loading. [1, 2]
• Microscopic cracks initiate at stress concentrations such as holes, grain boundaries, or composite interfaces when loads are below the yield strength. [2]
• Each loading cycle typically produces a striation that marks the incremental growth of a fatigue crack on the fracture surface. [2, 5]
• Some ferrous and titanium alloys have a distinct fatigue limit, whereas materials like aluminium and copper do not. [3]

Still open

• Early nineteenth-century theories attributed railway axle failures to metal crystallisation due to a brittle fracture appearance, but this explanation has since been disproved.

Where to go next

• how it workedWhat is a fatigue limit in engineering?
• how we knowHow do striations form on fracture surfaces?
• the bigger pictureHow is fracture mechanics applied to structural failures?
• whenWhy did nineteenth-century railway axles break suddenly?
• compared withHow do polymers differ from metals in fatigue resistance?
• an unexpected connectionWhat connects a scientific failure mode to a 1985 jazz fusion album?The engineering term metal fatigue shares its exact name with a 1985 musical album by Allan Holdsworth.

Sources

• [1]fatigue (Wikidata Q507234) · CC0 1.0
• [2]Fatigue (material) · CC BY-SA 4.0
• [3]Fatigue limit · CC BY-SA 4.0
• [4]Metal Fatigue · CC BY-SA 4.0
• [5]Striation (fatigue) · CC BY-SA 4.0