The fracture toughness of a material that has thickness greater than some minmum calculated value.

Plane-strain fracture toughness. The minimum value of Kc for any given material and condition, which is attained when rapid crack propagation in the opening mode is governed by plane-strain conditions.

The minimum value of KC. Represents the fracture toughness of a material independent of crack length, or loading system. Units are MPa/m or ksi/in.