Definition
Fatigue is a damage mechanism in which repeated cyclic loading (even at stress levels far below the material's static ultimate strength) initiates and gradually grows a crack until the remaining cross-section fails suddenly. It is distinguished by its cyclic-loading cause and characteristic fracture surface, distinct from a one-time overload failure.
Key facts
- Caused specifically by repeated cyclic loading, not a single overload: it can occur well below the material's static breaking strength.
- Progresses through crack initiation, gradual crack growth, and final sudden fracture once remaining cross-section is too weak.
- Fracture surfaces typically show distinctive features (beach marks, striations) that distinguish fatigue from a single overload break.
- A key concept in rotating equipment (shafts, couplings) and any component subject to repeated stress cycling.
What does Fatigue reveal about failures?
Fatigue is a progressive material failure process driven by repeated cyclic stress (vibration, repeated starts and stops, rotating bending) that initiates a microscopic crack at a stress concentration point and grows it incrementally with each cycle until the remaining material cannot support the load and fractures suddenly.
How do teams use Fatigue in failure analysis?
Fatigue is recognized through its characteristic fracture surface pattern (often showing beach marks or striations that record incremental crack growth) combined with evidence of repeated cyclic loading in the component's operating history, distinguishing it from a single overload fracture or from corrosion-driven cracking.
FAQ
Frequently asked questions
What does material fatigue mean under repeated loading?
Material fatigue means repeated cyclic loading initiates and gradually grows a crack, even at stress levels well below the material's static breaking strength, until the remaining cross-section fails suddenly.
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