A critical assessment of the effect of indentation spacing on the measurement of hardness and modulus using instrumented indentation testing

With the advances in instrumented indentation systems and testing methodologies, high speed indentation mapping with indents that take less than a second is now possible. This can be gainfully used to measure the local mechanical properties of multi-phase alloys and small volumes of materials with high throughput, which brings into question the minimum spacing between indents required to prevent interactions from neighboring indents. In this study, extensive indentation experiments (~50,000) and finite element simulations are carried out for a wide range of materials to systematically determine the minimum spacing of indents. It was found that a minimum indent spacing of 10 times the indentation depth is sufficient to obtain accurate results for a Berkovich indenter. This is less than half of the commonly followed criteria of spacing the indents three times the lateral dimension (or 20 times the depth). Similar results were also found for other indenter geometries. It was found that non-overlapping plastic zones are not a requirement for determining the minimum indent spacing and the new criteria is rationalized by simple energy arguments. These results significantly enhance the capabilities of indentation mapping technique which is recently being used as a critical characterization tool for accelerating materials development. Keywords: Hardness, Elastic property, Finite element analysis, Nanoindentation, Mapping