Modeling analysis of the indentation-derived yield properties of metallic multilayered composites

The determination of overall mechanical properties of small-scale composite structures, such as multilayered thin films, frequently relies on the indentation technique. In this study, finite element modeling is employed to examine the relationship between indentation hardness and overall yield strength of multilayered materials. For simplicity, the laminated composite is taken to consist of alternating layers of two elastic-perfectly plastic materials. The overall yield strength under uniform far-field loading is first quantified. Indentation loading of the layered structure is then simulated to cover a wide range of indentation depth well into multiple layers. The systematic hardness values thus obtained are converted to corresponding flow stresses using the numerically established relationship for homogeneous materials. It is found that the indentation-derived strength consistently underestimates the composite yield strength, within the scope of the present continuum-based approach. Friction at the contact surface is also found to play a significant role. Relevant issues on applying indentation techniques to probe overall mechanical properties of metallic multilayers are discussed.