Engineering Calculation of Fracture Toughness of Materials with Chevron-Notched Specimens

A new method of crack resistance of metal materials is given for small-sized chevron-notched specimens. Specific fracture energy (SFE) is offered to be the main characteristic of fracture toughness. A relation for notch edges opening lambda(e) versus the applied external force, crack length and chevron angle was found theoretically. It makes it possible to evaluate variations of compliance of a specimen in the process of crack spreading without the "loading-unloading" regime. Unlike linear fracture mechanics, this technique does not require special conditions on the size of the plastic zone in the vicinity of the crack tip. It is shown that the measured displacement of the notch edges opening lambda contains the term lambda(p), which relates to some plastic deformation of a specimen and does not depend on the crack growth. In general, lambda = lambda(e) + lambda(p).