Linear Elastic Fracture Mechanics (LEFM)
Definition
The branch of fracture mechanics valid when the plastic zone at the crack tip is small relative to the crack length and component dimensions. Its central result is the K-K_IC comparison.
- Valid when
- Plastic zone is small relative to crack and part size
- Key result
- Comparison of stress intensity K to fracture toughness K_IC
- Field
- Fracture mechanics, failure analysis
Common questions
What happens when the plastic zone is not small enough for LEFM to apply?+
The linear assumptions break down and analysts must switch to elastic plastic fracture mechanics, which accounts for the larger zone of yielding around the crack tip that LEFM ignores.
What does comparing K to K_IC actually tell an investigator?+
If the calculated stress intensity factor K reaches or exceeds the material's fracture toughness K_IC, the crack was capable of propagating catastrophically under the load present, a key finding in a failure investigation.
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...
- 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...
- Stress Intensity Factor (K)
- A parameter, in MPa√m, describing the amplitude of the stress field near a crack tip for a given geometry and load. When...