Stress-Concentration Factor (Kt)
Definition
A dimensionless multiplier representing the ratio of the actual maximum stress at a notch, hole, or corner to the nominal stress in the undisturbed cross-section; higher Kt increases fatigue susceptibility.
- Symbol
- Kt
- Definition
- Actual peak stress over nominal stress
- Units
- Dimensionless
- Higher Kt effect
- Increased fatigue susceptibility
Common questions
Where on a failed part does Kt tend to be highest?+
Kt peaks at geometric discontinuities such as sharp notches, small-radius corners, drilled holes, and threads, which is why fatigue cracks in a fractographic examination so often originate at those features rather than on a smooth surface.
How does a failure analyst use Kt in practice?+
The analyst compares the part's design or as-built geometry against reference charts or finite-element results to estimate Kt at the fracture origin, then weighs that value against the applied nominal stress to judge whether the geometry alone explains a premature failure.
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...
- 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...
- 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-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...