Effect of adsorption on nanoindentation test

The contact stiffness widely used in nanoindentation test is based on the Hertzian contact theory for zero-interfacial friction (slip boundary condition), in which the effect of adhesion energy is ignored. However, in the real situation, the adhesion energy may not be negligible when the contact is adhesive. A solution of the contact stiffness is derived by using adhesive contact theory for both frictionless condition (the famous Johnson-Kendall- Roberts theory) and the sticky condition. The results show that the nominal contact stiffness depends on the adhesion energy and indenter size as well as the load applied to indenter. For a large size of indenter and small load, the adhesion energy controls the contact process; while for a large load, the elastic deformation dominates, in which the nominal contact stiffness approaches the result based on the Hertzian contact theory.