Stress Intensity Factor (K)
Definition
A parameter, in MPa√m, describing the amplitude of the stress field near a crack tip for a given geometry and load. When K reaches the critical value K_IC, the crack propagates unstably.
- Symbol
- K
- Units
- MPa times root metre
- Describes
- Stress field near a crack tip
- Critical value
- K_IC, fracture toughness
Common questions
What happens once K reaches K_IC?+
The crack, previously stable or growing slowly under cyclic loading, propagates unstably and rapidly through the remaining material, which is the mechanism behind sudden catastrophic fracture rather than gradual fatigue failure.
How is K used in a forensic engineering investigation?+
An analyst calculates K for the crack size and loading present at the time of failure and compares it against the material's known K_IC, to determine whether the fracture was consistent with an overload event or with slow fatigue growth reaching a critical crack length.
Related terms
- Elastic-Plastic Fracture Mechanics (EPFM)
- The extension of fracture mechanics to ductile materials where significant plasticity occurs before fracture. The J-integral and crack tip opening displacement (CTOD)...
- Fracture Toughness (K_IC)
- The critical stress intensity factor measured under plane-strain conditions. It is a material property representing the maximum K a component can tolerate...
- Griffith Criterion
- The energy-balance condition derived by A.A. Griffith in 1921: a crack extends when the elastic strain energy released per unit area of...
- Linear Elastic Fracture Mechanics (LEFM)
- The branch of fracture mechanics valid when the plastic zone at the crack tip is small relative to the crack length and...
- Plane Stress vs Plane Strain
- In thin sections the crack-tip region contracts freely in the thickness direction (plane stress), giving higher apparent toughness. In thick sections that...