The use of the loading curve to assess soft coatings

A theoretical equation to determine the dependence of load P on the displacement h for plastic and elastic deformations under a Berkovich indenter is derived. This theoretical P–h relation was fitted to the experimental data for organic–inorganic hybrid coatings and glass and used to determine the elastic modulus and hardness. Either a plot of P/h2 vs. h2 (or h) or a plot of ∂P/∂h2 vs. h2 (or h) can be used to assess fracture. Advantages and disadvantages of these approaches are discussed.