Griffith's equation

I teach Materials Science to undergraduate engineering students. We devote 2 or 3 lectures on Fracture where we mainly introduce Griffith's formula and the stress intensity formula. I face a difficulty in reconciling the two which I would lke to present here.

The Griffiths equation gives the fracture stress s for a given crack size c:

s=sqrt[2 E g/ (p c)] (1)

The stress concentration formula gives the max stress at the crack tip as

s=s0 [1+2 sqrt (c/r)] (2)