Effect of surface detection error due to elastic–plastic deformation on nanoindentation measurements of elastic modulus and hardness

Elastic modulus and hardness are commonly measured using nanoindentation. Calculating these properties from measured force–displacement curves typically requires knowledge of the contact depth of the indenter into the specimen. However, surface detection methods in many nanoindentation experiments can lead to an error in the contact depth measurement and, subsequently, the measured properties. Here, the contributions of elastic and plastic deformations to surface detection errors in nanoindentation experiments are examined through experiments and modeling. The model is used to quantify errors in elastic modulus and hardness measurements due to elastic–plastic deformation during surface detection as a function of the specimen properties, indenter geometry, preload, and contact depth. Nanoindentation measurements on polystyrene, an aluminum alloy, and fused silica specimens with a Berkovich indenter are used to illustrate the effects of surface detection error and are compared to the model. The experiments and model both demonstrate that surface detection error can lead to measurement of apparent depth-dependent properties in homogenous materials.