Effect of adhesion energy on the contact stiffness in nanoindentation

The effect of surface interaction on nanoindentation testing using a rigid conical indenter is analyzed. A relation between the indentation depth and the indentation load is established as a function of the adhesion energy between the indenter and the surface of an elastic material. A closed-form solution of the contact stiffness for adhesive contact is obtained. The contact stiffness in the presence of surface interaction is always less than that for contact without surface interaction at the same indentation depth, while it is always larger than that for adhesion-less contact subjected to the same indentation load. A lower bound is established, which determines the working zone to operate to avoid the effect of surface interaction in the characterization of the contact modulus.