What is the crack-tip stress intensity factor of an embedded crack under mode II shear?

Hi, 

From textbook of fracture mechanics, we know that for an embedded crack subjected to mode I stress state, KI=(2/π)σ√πa, while 2a is the crack size.

But for a embedded crack subjected to a pure shear stress τ, what is the stress intensity factor at the crack-tip?

Thank you 

Ruitao