Stress-Corrosion Cracking (SCC)
Definition
A failure mode combining sustained tensile stress with a specific corrosive environment, producing branching, often intergranular cracks that grow at stress intensities well below the fracture toughness of the dry material.
- Fracture pattern
- Intergranular cracks with branching morphology
- Required conditions
- Sustained tensile stress and a specific corrosive environment
- Stress level
- Occurs below the material's static yield strength and fracture toughness
Common questions
What makes stress-corrosion cracking different from normal corrosion?+
SCC combines two conditions that amplify each other: a sustained tensile load and a corrosive environment. Either alone would be manageable, but together they cause cracks to form and grow at stress levels well below what would normally break the material. The cracks often grow along grain boundaries, producing a branching pattern.
Why does SCC happen at stresses below the material's yield strength?+
In a corrosive environment, sustained tensile stress accelerates damage at the atomic level, creating pathways for cracks to propagate. The corrosion weakens the material locally while stress concentrates at crack tips, allowing failure to occur at stress intensities below the material's fracture toughness.
How would a forensic engineer identify stress-corrosion cracking in a failed component?+
Look for intergranular fracture patterns and branching cracks. The fracture surface often shows a specific morphology tied to the corrosive environment. Fractography and knowledge of the operating conditions (load history and exposure to a specific corrosive medium) help confirm the 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,...
- Corrosion Fatigue
- Fatigue crack initiation and growth accelerated by a corrosive environment. Unlike SCC, it does not require a specific environment-material combination and can...
- Crevice Corrosion
- Corrosion in confined geometry , under gaskets, at lap joints, between fastener and plate , driven by oxygen depletion and acidification inside...
- 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...
- Fractography
- The systematic examination and interpretation of fracture surfaces to determine the mechanism, origin, and propagation direction of fracture; uses optical and scanning...
- Galvanic Corrosion
- Electrochemical attack that accelerates the dissolution of the more active (anodic) metal when two dissimilar metals are electrically coupled in an electrolyte.
- MCAS
- Maneuvering Characteristics Augmentation System; the Boeing 737 MAX software feature that repeatedly commanded nose-down stabiliser trim based on a single AoA sensor...
- Pitting Corrosion
- Localised attack producing narrow, deep craters where the passive film breaks down. Pitting is self-propagating once initiated because the pit interior becomes...
- 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...
Explained in these topics
- Corrosion Failure ModesA failure mode combining sustained tensile stress with a specific corrosive environment, producing branching, often intergranular cracks that grow at stress in...
- Forensic Engineering: Failure Analysis and FractographyA failure mechanism combining sustained tensile stress with a corrosive environment; typically produces intergranular fracture at stresses well below the mater...