Effect of constraint on interface fracture toughness

Hi All,

I have a question in my mind, we all know that the fracture toughness of isotropic, homogeneous materials is dependent on state of stress (plane strain and plane stress). It is higher in case of plane stress and decreases as the constraint increases and attains a constant value which we call "plane strain fracture toughness". But, what about the fracture toughness in interfaces? or fracture of thin layer bonded between two substrates (adhesive type)? I am sure that it will be a function of this as well.

My question is, is anybody know of a study which shows this effect. How can we apply fracture toughness calculated in plane strain conditions to situations of plane stress or some constraint inbetween these two? I dont know whether my questions are meaningful but it would be great if some one can help.

Thanks,

Siva