What is fracture toughness and critical crack size?

Fracture toughness is a material property that quantifies a material's ability to resist crack propagation and failure under applied stress. It represents the critical stress intensity factor where crack propagation suddenly becomes rapid and unlimited. A crack continues to grow under cyclic loading until it reaches a critical size, which occurs when the stress intensity factor exceeds this fracture toughness limit.

What we know

• Fracture toughness is the critical stress intensity factor of a sharp crack where propagation suddenly becomes rapid and unlimited. [2]
• Plane strain conditions provide the lowest fracture toughness value, which serves as a true material property. [2]
• A fatigue crack grows with each loading cycle until it reaches a critical size when the stress intensity factor exceeds the material's fracture toughness. [5]
• G. Irwin found in 1957 that any loading state on a crack could be reduced to a combination of three independent stress intensity factors: opening, sliding, and tearing modes. [3]

Where to go next

• how it workedHow does linear elastic fracture mechanics characterize crack tips?
• the bigger pictureWhat happens during material fatigue and cyclic loading failure?
• compared withHow do plane strain and plane stress conditions affect fracture behavior?
• what caused itWhat is stress corrosion cracking?
• an unexpected connectionHow did nineteenth-century engineers misunderstand metal railway axle failures?

Sources

• [1]fracture toughness (Wikidata Q911969) · CC0 1.0
• [2]Fracture toughness · CC BY-SA 4.0
• [3]Fracture mechanics · CC BY-SA 4.0
• [4]Fracture · CC BY-SA 4.0
• [5]Fatigue (material) · CC BY-SA 4.0