Elastic-Plastic Fracture Mechanics (EPFM)
Definition
The extension of fracture mechanics to ductile materials where significant plasticity occurs before fracture. The J-integral and crack tip opening displacement (CTOD) are the EPFM equivalents of K_IC.
- Field
- Extension of fracture mechanics
- Applies to
- Ductile materials with plasticity before fracture
- Key parameters
- J-integral, CTOD
- Analogue in LEFM
- K_IC (stress intensity factor)
Common questions
Why can't linear elastic fracture mechanics be used for ductile metals?+
Linear elastic fracture mechanics assumes the material stays elastic right up to the crack tip, but ductile metals develop a significant plastic zone before they fracture, which invalidates that assumption and requires the J-integral or CTOD to properly characterise the failure.
How is EPFM applied in a forensic failure investigation?+
An examiner uses EPFM parameters to judge whether a fracture in a ductile component, such as a structural steel part or a pipe, is consistent with overload failure at the material's known toughness or points instead to a pre-existing flaw, fatigue crack, or degraded material property.
Related terms
- 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...
- 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...