An energy-based method to extract plastic properties of metal materials from conical indentation tests

Based on dimensional analysis and finite element computations, an energy-based representative strain for conical indentation in elastoplastic materials has been proposed to establish an explicitly one-to-one relationship between the representative stress σ_r, the indentation loading curvature C, and the ratio of reversible work W_e to total work W_t performed by the indenter, i.e., σ_r/C = F₀(W_e/W_t), where σ_r is the flow stress corresponding to the representative strain. The relationship provides a very simple method to evaluate the representative stress σ_r from the three directly measurable quantities W_e, W_t, and C. Numerical examples and further theoretical analysis reveal that a unique, stable solution can be obtained from the present method for a wide range of material properties, including both highly plastic materials (e.g., Ni for which E/σ_y = 1070) and highly elastic materials (e.g., materials for which E/σ_y = 25 and n = 0.5), using indenters with different tip apex angles. Based on the representative strains and stresses given by two indenters with different tip apex angles, e.g., (σ_r,80, ϵ_r,80) and (σ_r,65, ϵ_r,65), the plastic properties of materials, i.e., the yield strength σ_y and strain hardening exponent n can be further determined.