Fatigue Fracture
Definition
Fracture resulting from repeated cyclic loading, typically at stresses below the static yield strength. The fracture surface has characteristic markings (beach marks, striations) absent from single-load fractures.
- Cause
- Repeated cyclic loading, often below static yield strength
- Diagnostic markings
- Beach marks, striations
- Contrast
- Absent from a single-overload fracture
- Field
- Fractography, mechanical failure analysis
Common questions
How do beach marks and striations differ from each other on a fatigue fracture surface?+
Beach marks are macroscopic curved bands visible to the naked eye, reflecting changes in loading conditions or crack-growth rate over time, while striations are microscopic lines seen only under high magnification, with each striation typically corresponding to a single load cycle.
Why does identifying fatigue matter in a failure investigation?+
Recognising a fatigue origin points the investigator toward a design, material, or maintenance issue that allowed a crack to grow slowly over repeated cycles, which is a very different root cause and liability picture than a single overload event snapping an otherwise sound part.
Related terms
- Beach Marks
- Macroscopic curved bands on a fatigue fracture surface, visible without magnification, produced by changes in crack growth rate during service (load changes,...
- Fatigue Striations
- Microscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at...
- Multi-Site Damage (MSD)
- The simultaneous presence of fatigue cracks at multiple adjacent fastener holes or structural features, characteristic of ageing aircraft fuselage and other riveted...
- Ratchet Marks
- Radial steps or ridges on a fatigue fracture surface separating adjacent regions that initiated from separate sites. They run from the component...
- Stress Intensity Range (ΔK)
- The difference between the maximum and minimum stress intensity factor in one loading cycle, ΔK = K_max - K_min. The Paris law...