Fracure mechanics

Hi Every body,

I know that the crack propagation energy release rate G is by defination the release of elastic energy and potential energy of loads per unit area of crack extension and for a linear body loaded by a single load P is given by :

G=P^2/(2b)*dc/da

Any body know if instead of load P, moment M is being used what would be formulation?

I really need this one

Thank you,

Parisa