When designing with ductile high strength metals for safety critical cases, it is important to understand the behavior around defects and cracks, when otherwise just the basic tensile properties would be enough. Resistance to localized failure (as opposed to bulk tensile strength) is generally described by the umbrella term of fracture toughness. When that failure is more gradual than a sudden critical break, JIc is a toughness metric used to describe the point at which tearing starts.

The most prevalent application is in the power generation sector, where highly detailed modelling is expected and designs must provide for damage tolerance to flaws. That is to say failure without catastrophy – obviously a matter of the highest profile in nuclear power!