Elastic-plastic Fracture Mechanics Behavior of Graphite

4 Elastic-plastic Fracture Mechanics Behavior of Graphite 

Griffith derived his relationship for glass where R consists only of surface energy. In the case of metals, R is mainly plastic energy associated with the formation of a crack tip plastic zone. It is obvious from Eq. 9 that, for plane stress, 

That fraction of the applied work which is not consumed in the elastic-plastic deformation remains to create the new crack surface, i. e., the crack driving force. Therefore, a nonlinear fracture toughness,, may be defined as follows  

The difference between the work input and the elastic stored energy is the crack growth resistance, R, 

As with the purely elastic case, the energy values associated with elastic-plastic fracture may be ascertained from the load versus load-point deflection diagram for a cracked body as shown in Fig. 5. 

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