Crack-extension force release rate

Gc is a material property which is referred to as the toughness, critical strain energy release rate or crack extension force. It is effectively the energy required to increase the crack length by unit length in a piece of material of unit width. It has units of J/m. ... 

To obviate this inadequacy, Griffith s equation had to be modified to include the energy expended in plastic deformation in the fracture process. Accordingly, Irwin defined a parameter, G, the strain-energy-release rate or crack extension force, which he showed to be related to the applied stress and crack length by the equation ... 

If the material is not perfectly brittle, i.e., there are energy dissipating mechanisms in addition to the creation of new surfaces, then we introduce a term G, which is an energy (its units are J/m ) representing crack extension by all the available processes. You will find Gc referred to as total work of fracture, crack extension force, and strain energy release rate. 

Most fracture experiments are conducted under normal loading conditions (mode I) and the fracture properties are described in terms of the strain energy release rate, or crack extension force, Gj. If a steadily increasing load, P, is applied to a joint, a critical value. Pc will be reached at which crack extension will just begin. At this condition, Gi is referred to as the fracture energy, or fracture toughness, G. Various test specimen... 

G, [kNm" ] is the elastic stress energy release rate, meaning that it describes the rate at which the energy for crack propagation is supplied. Gj as equal to dV/dc is also called the crack extension force and is related to elastic properties of the material and element and to the applied load system. 

The energy release rate, or crack driving force, which is used to predict crack stability. The critical value of the energy release rate at which crack extension occurs, often referred to as the fracture toughness, or adhesion energy the subscript indicates that the quantity refers to the interface toughness (as opposed to a bulk material). 

When cracks extend in mode I loading in LEFM they release elastic strain energy in the surrounding stress field. The rate of release of such energy with crack extension can be considered as a generalized crack-driving force and is alternatively a direct representation of the work of fracture when a critical condition Gic for crack extension is reached. 

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