Fatigue Striations
Definition
Microscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at magnifications of 1,000-10,000x; striation spacing is proportional to stress intensity range.
- Visibility
- Visible on a fatigue fracture surface under SEM at magnifications of 1,000-10,000x.
- When they form
- During Stage II crack growth under repeated loading cycles.
- Spacing relationship
- Striation spacing is proportional to stress intensity range.
Common questions
What do fatigue striations look like under a microscope?+
They are microscopic parallel lines visible on a fracture surface under a scanning electron microscope (SEM) at 1,000-10,000x magnification. Each line marks the position where the crack stopped and started between individual loading cycles.
Why are striations spaced differently on the same fracture?+
The spacing between striations directly reflects how far the crack advanced during that loading cycle. Greater spacing means the crack grew more per cycle, usually because stress intensity was higher at that point in the failure history.
How do fatigue striations help investigators?+
They reveal the loading history of the component and confirm that failure occurred from repeated stress cycles rather than a single catastrophic load. The pattern of striation spacing can show how conditions changed over time before final fracture.
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,...
- Damage-Tolerant Design
- A structural-design philosophy that assumes cracks will form and specifies inspection intervals short enough to detect and repair cracks before they reach...
- Ductile Dimples
- Microscopic cup-shaped depressions visible on a ductile overload fracture surface under SEM, formed by nucleation, growth, and coalescence of microvoids at second-phase...
- Fatigue Fracture
- Fracture resulting from repeated cyclic loading, typically at stresses below the static yield strength. The fracture surface has characteristic markings (beach marks,...
- Fractography
- The systematic examination and interpretation of fracture surfaces to determine the mechanism, origin, and propagation direction of fracture; uses optical and scanning...
- MCAS
- Maneuvering Characteristics Augmentation System; the Boeing 737 MAX software feature that repeatedly commanded nose-down stabiliser trim based on a single AoA sensor...
- 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...
- Progressive Collapse
- A failure mode in which local structural failure triggers a sequence of failures in adjacent members, resulting in collapse disproportionate to the...
- Ratchet Marks
- Radial steps or ridges on a fatigue fracture surface separating adjacent regions that initiated from separate sites. They run from the component...
- River Patterns
- Fan-shaped or river-delta-like markings on brittle-cleavage fracture surfaces that indicate crack propagation direction; rivers diverge from the origin and converge toward the...
- S-N Curve
- A plot of cyclic stress amplitude (S) against the number of cycles to failure (N), used to characterise a material's fatigue life;...
- Safe-Life Design
- A structural-design philosophy where a component is retired from service before its predicted fatigue life is consumed; does not require crack detection...
Explained in these topics
- Fatigue Fracture: Beach Marks and StriationsMicroscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at magnifications of...
- Forensic Engineering: Failure Analysis and FractographyMicroscopic parallel lines visible on a fatigue fracture surface under SEM, each corresponding to one loading cycle; spacing reflects the crack advance per cyc...