A new modified ECM approach on the identification of plastic anisotropic properties by spherical indentation

Abstract

This paper proposes a new approach on the identification of plastic anisotropic properties (σY, n, m), which is based on new modified expanding cavity model (ECM). The new ECM incorporates Hill's an anisotropic yield criterion in 1948 by equivalent transformation of stress expression form from spherical polar coordinate system to space rectangular coordinate system, and considers piling-up or sinking-in effect by introducing volume correction factor t as a semi-theoretical function. Through the indentation analysis for new ECM, the representative stress-strain method can characterize indentation mean pressure and uniaxial flow properties. Meanwhile, nonlinear functional relations between indentation response and plastic anisotropic properties are established. The effectiveness and reliability of new developed ECM approach are verified by the comparisons between identified properties and input properties in spherical indentation simulations, the comparisons between plastic anisotropic properties identified from instrumented indentation experiments and uniaxial compression experiments, and the comparisons between representative flow stress-strain points and compression experimental curves. The identified results are obtained by iterative calculations using the trust-region techniques based on the nonlinear least-square method. Excellent agreement is achieved. Finally, it is demonstrated that the proposed approach is reliable and useful for identification of plastic anisotropic properties of various anisotropic materials.