Fracture Toughness determines the amount of stress required to propagate an existing flaw or defect in specific materials. Since traditional methods of destructive testing cannot always predict how a material will behave with a defect, fracture toughness is very important in the design stage.
Crack-Tip Opening Displacement (CTOD) is used as a type of fracture toughness testing to determine if a material is appropriate for strenuous working conditions. CTOD testing is the measure of plastic deformation prior to failure in a pre-cracked sample. This type of test is a variation of fatigue testing that has load rates more representative of in-service conditions.