Fracture toughness is a property that describes the ability of a material to resist fracture and is one of the essential properties of any material for many design applications.
In materials science, fracture toughness is the critical stress intensity factor of a sharp crack, where crack propagation suddenly becomes rapid and unrestricted. The thickness of a component affects the constraint conditions at the tip of a crack, with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest value of fracture toughness, which is a material property. The critical value of the stress intensity factor under Mode I loading measured under plane strain conditions is known as the plane strain fracture toughness.