Analysis of Microindentation Unloading Curves based on Representative Strain Approach with Closed-Form Applications

Indentation analysis based on the representative strain offers an effective way of obtaining material elastoplastic properties from the reverse analysis of indentation load-displacement curve. In this paper, its approach is employed to analyze the unloading force-depth curves obtained from a sharp microindentation test. By using the unloading work and residual penetration depth as parameters characterizing unloading, two different formulations of representative strain/stress are proposed, respectively, with very simple functional forms. When combined with the established framework of loading curves, the plastic properties and/or elastic properties of a material can be derived in closed-form using the loading curvature, unloading work, and residual depth measured from one sharp indentation test.