3-D modeling of nanoindentation experiment on a coating-substrate system

The validity of indentation tests for the characterization of the mechanica l properties of coatings relies greatly on the indentation depth. Deep inde ntation concludes to unreliable results due to the substrate effect on the measured properties. At shallow depths the size effect can also be an impor tant error factor. The purpose of the present study is the determination of the critical ratio of coating thickness to indentation depth, up to which the substrate properties have a negligible effect on the force versus inden tation depth curve and thus on determined mechanical properties of the coat ing. The analysis required, was conducted using finite element method. A sp herical (ball) indenter was used and a three dimensional model of the inden ter/coating-substrate system was applied. The effect of the coating to subs trate Yield strength ratio, on the critical coating thickness to indentatio n depth ratio, was investigated for three different coating to substrate Yo ung's modulus ratios. The results of this work provide considerable insight for the determination of the confidence indentation depth during micro-ind entation for layered systems with different properties.