A method for measuring the contact area in instrumented indentation testing by tip scanning probe microscopy imaging

The determination of the contact area is a key step in deriving mechanical properties such as hardness or an elastic modulus by instrumented indentation testing. Two families of procedures are dedicated to extracting this area: on the one hand, post-mortem measurements that require residual imprint imaging, and on the other hand, direct methods that only rely on the load vs. penetration depth curve. With the development of built-in scanning probe microscopy imaging capabilities such as atomic force microscopy and indentation tip scanning probe microscopy, last-generation indentation devices have made systematic residual imprint imaging much faster and more reliable. In this paper, a new post-mortem method is introduced and further compared to three existing classical direct methods by means of a numerical and experimental benchmark covering a large range of materials. It is shown that the new method systematically leads to lower error levels regardless of the type of material. The pros and cons of the new method vs. direct methods are also discussed, demonstrating its efficiency in easily extracting mechanical properties with enhanced confidence.