What does Griffiths formula measure?

[avito009]

What does this formula measure? c= \sqrt{2EY/\pi} This topic is from fracture mechanics. Does this formula tell you how much stress is required to cause the crack to increase?

 

[Simon Bridge]

What does this formula measure? [$C= \sqrt{2E\gamma /\pi}$] This topic is from fracture mechanics. Does this formula tell you how much stress is required to cause the crack to increase?

... no. It is an attempt to model the empirical constant in the relation between the stress at fracture, and the fracture length: \sigma_f/\sqrt a = C##
https://en.wikipedia.org/wiki/Fracture_mechanics