Ductile Dimples
Definition
Microscopic cup-shaped depressions visible on a ductile overload fracture surface under SEM, formed by nucleation, growth, and coalescence of microvoids at second-phase particles; indicate substantial plastic deformation before fracture.
- Visible under
- Scanning electron microscope (SEM)
- Formation
- Microvoid nucleation, growth, coalescence
- Nucleation site
- Second-phase particles/inclusions
- Indicates
- Substantial plastic deformation before fracture
Common questions
How do examiners tell ductile dimples apart from brittle fracture features on a fracture surface?+
Ductile dimples appear as rounded cup-shaped depressions with a fibrous, matte texture, while brittle fractures show flat cleavage facets or a granular, shiny surface. The presence of dimples alone is treated as strong evidence of an overload failure mechanism rather than fatigue or brittle cracking.
Can dimple shape reveal the direction of loading in a failure?+
Yes, dimples elongated in one direction rather than equiaxed can indicate shear loading, and their orientation relative to the fracture edge helps reconstruct the local stress state at the moment of failure.
Related terms
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- Fatigue Striations
- Microscopic parallel marks on a fatigue fracture surface, formed during individual loading cycles in Stage II crack growth. Visible by SEM at...
- Fractography
- The systematic examination and interpretation of fracture surfaces to determine the mechanism, origin, and propagation direction of fracture; uses optical and scanning...
- MCAS
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- 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...