Determination of mode I and II adhesion toughness of monolayer thin films by circular blister tests

Mechanical models are developed to determine the mode I and II adhesion toughness of monolayer thin films using circular blister tests under either pressure load or point load. The interface fracture of monolayer thin film blisters is mode I dominant for linear bending with small deflection while it is mode II dominant for membrane stretching with large deflection. By taking the advantage of the large mode mixity difference between these two limiting cases, the mode I and II adhesion toughness are determined in conjunction with a linear failure criterion. Thin films under membrane stretching have larger adhesion toughness than thicker films under bending. Experimental results demonstrate the validity of the method.