Fracture Toughness

Critical value of the stress intensity factor for which crack extensions occurs. The fracture toughness Kc, is a measure of the resistance of a material to the propagation of a crack. It can be measured by loading a sample containing a deliberately-introduced crack of length 2c and then recording the tensile stress σ at which the crack propagates. Fracture toughness is then:


where
Y = geometric factor, near unity, which depends on details of the sample geometry.

Kc has well defined values for brittle materials (ceramic, glasses, many polymers and low toughness metals like cast iron).

In ductile materials, a plastic zone develops at the crack tip, which introduces new features into the way cracks propagate. This necessitates more complex characterisation.
Conversions
1 ksi in1/2=1.098843 MPa m1/2

See also: Crack, Fracture Stress, Fracture Testing.

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Subjects: Mechanical Engineering