Effect of the spherical indenter tip assumption on nanoindentation

One of the interests and challenges of nanoindentation is determining the shear stress at the onset of plastic yielding, which corresponds to dislocation nucleation. To extract this stress information from experimental load-displacement data, a spherical tip shape is usually assumed. However, it is well known that indenter tips have irregular shapes, especially at the small-length scales that are important for small loads. This will significantly affect the stress distribution under the indentation surfaces. In this work, an indenter tip shape is measured by atomic force microscopy. The measured indenter shape is input into a finite element analysis model for indentation simulations on 〈111〉-oriented single-crystal Al samples in the elastic regime. The resulting stresses, indentation force, and contact area are analyzed and compared to results from a fitted spherical indenter. The deviation of the assumed spherical indenter tip from the real measured indenter tip is studied.