Abstract:One of the primary features of nano-indentation technique is that the contact area induced by an indenter is indirectly measured by a relationship between the penetration depth and the known geometry of the indenter. However, this indirect measurement occasionally leads to inaccurate properties of the indented material. The objective of this study is to investigate the effects of E^*/σ_r and the strain hardening exponents n of materials on the behaviors of pile-up and sink-in in nano-indentation and to predict n values of materials from the residual indentation impressions. The relations between the residual indentation profile and n value of the indented material were identified by dimensional analysis. Also, they were numerically formulated using FE analysis of nano-indentation for 140 different combinations of elastic-plastic parameters such as E, σ_y and n. The parameters of h_rp/h_m, h_erp/h_m, R_r/h_m and H_O&P/H_real were introduced as various dimensionless parameters to represent and quantify the residual indentation profile after indentation. They were subsequently characterized as dimensionless functions using n and E^*/σ_r values. Finally, the validity of these functions was verified through 3D FE analysis of nano-indentation for Al 6061-T6 and AISI 1010 materials.

Key words: nano-indentation; pile-up; sink-in; strain hardening exponent; FE simulation