Effect of material heterogeneity on the evolution of internal deformation during nanoindentation

Abstract

The effect of material heterogeneity on the indentation behaviour is studied numerically using the finite element method. The material system of concern is the aluminium (Al)/silicon carbide (SiC) multilayered thin films above the silicon (Si) substrate. The numerical model features the explicit composite structure indented by a conical diamond indenter within the axisymmetric simulation framework. Attention is devoted to the evolution of stress and deformation fields in the material during the indentation loading and unloading processes. It is found that the layered composite, consisting of materials with distinctly different mechanical properties, results in unique deformation patterns. Significant tensile stresses can be generated locally along certain directions, which offer a mechanistic rationale for the indentation-induced internal cracking observed experimentally. The unloading process also leads to an expansion of the tension-stressed area, as well as continued plastic flow in parts of the Al layers. The unloading response in this heterogeneous material is therefore much more complex than the conventional purely elastic recovery process in homogeneous materials.