Griffith-Orowan criterion

The Griffith-Orowan criterion for spontaneous fracture is defined as the critical crack depth at which the slope dUj/da changes abruptly to negative values as shown in Fig. 6.1. Mathematically, this condition corresponds to... 

Figure 6.1 Griffith-Orowan fracture criterion. (Courtesy of Prof. A. T. DiBene-detto.)...

This approach was later modified independently by Irwin (51,52) and Oro-wan and Weld (53) and Orowan (54) by including a strain energy release rate term to account for changes caused by small-seale plastic deformations at the crack tip and surfaces. Below, an expression is derived using the modified Griffith criterion for the occurrence of spontaneous fracture of a brittle material depicted in Fig. 6.1. 

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