Depth - sensing instrumented indentation with dual sharp

57 A methodology for interpreting instrumented sharp indentation with dual sharp indenters with different tip apex 58 angles is presented by recourse to computational modeling within the context of finite element analysis. The forward 59 problem predicts an indentation response from a given set of elasto-plastic properties, whereas the reverse analysis 60 seeks to extract elasto-plastic properties from depth-sensing indentation response by developing algorithms derived 61 from computational simulations. The present study also focuses on the uniqueness of the reverse algorithm and its 62 sensitivity to variations in the measured indentation data in comparison with the single indentation analysis on 63 Vickers/Berkovich tip (Dao et al. Acta Mater 49 (2001) 3899). Finite element computations were carried out for 76 64 different combinations of elasto-plastic properties representing common engineering metals for each tip geometry. 65 Young’s modulus, E, was varied from 10 to 210 GPa; yield strength, sy, from 30 to 3000 MPa; and strain hardening 66 exponent, n, from 0 to 0.5; while the Poisson’s ratio, n, was fixed at 0.3. Using dimensional analysis, additional closed67 form dimensionless functions were constructed to relate indentation response to elasto-plastic properties for different 68 indenter tip geometries (i.e., 50°, 60° and 80° cones). The representative plastic strain er, as defined in Dao et al. (Acta 69 Mater 49 (2001) 3899), was constructed as a function of tip geometry in the range of 50° and 80°. Incorporating the 70 results from 60° tip to the single indenter algorithms, the improved forward and reverse algorithms for dual indentation 71 can be established. This dual indenter reverse algorithm provides a unique solution of the reduced Young’s modulus 72 E∗, the hardness pave and two representative stresses (measured at two corresponding representative strains), which 73 establish the basis for constructing power-law plastic material response. Comprehensive sensitivity analyses showed 74 much improvement of the dual indenter algorithms over the single indenter results. Experimental verifications of these 75 dual indenter algorithms were carried out using a 60° half-angle cone tip (or a 60° cone equivalent 3-sided pyramid 76