Fractography
Definition
The systematic examination and interpretation of fracture surfaces to determine the mechanism, origin, and propagation direction of fracture; uses optical and scanning electron microscopy.
- Studies
- Fracture surfaces
- Determines
- Mechanism, origin, propagation direction
- Tools
- Optical and scanning electron microscopy
- Field
- Forensic engineering/materials failure analysis
Common questions
How does SEM add information beyond what optical microscopy shows on a fracture surface?+
SEM provides much higher magnification and depth of field than optical microscopy, revealing fine features like striations, dimples, and cleavage facets at the micron scale that identify the failure mechanism precisely, detail an optical microscope cannot resolve.
Can fractography determine the sequence of multiple fractures in a single failed component?+
Yes, through features like the fracture termination rule and ratchet marks, where a later-propagating crack leaves visible evidence of stopping at the free surface created by an earlier crack, letting examiners reconstruct the order fractures occurred.
What is the practical difference between fractography and fracture surface analysis as terms?+
They are closely related and often used interchangeably; fractography is generally the broader discipline covering methods and interpretation of fracture surfaces, while fracture surface analysis often refers to the specific act of examining one component's break to identify its failure mode.
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 Striations
- Microscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at...
- MCAS
- Maneuvering Characteristics Augmentation System; the Boeing 737 MAX software feature that repeatedly commanded nose-down stabiliser trim based on a single AoA sensor...
- Progressive Collapse
- A failure mode in which local structural failure triggers a sequence of failures in adjacent members, resulting in collapse disproportionate to the...
- 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...
- Stress-Concentration Factor (Kt)
- A dimensionless multiplier representing the ratio of the actual maximum stress at a notch, hole, or corner to the nominal stress in...
- Stress-Corrosion Cracking (SCC)
- A failure mode combining sustained tensile stress with a specific corrosive environment, producing branching, often intergranular cracks that grow at stress intensities...