Understanding indentation-induced elastic modulus degradation of ductile metallic materials

Noticeable degradation of the measured elastic moduli of ductile metals has been found in meso-/macroindentation tests. Although this phenomenon has been exploited to estimate the fracture properties of ductile metallic materials, the mechanism of the indentation-induced damage is rarely studied. Finite element simulations show that the finite stiffness of an indentation system can cause a false degradation of the effective indentation modulus. However, the decay pattern is different from that due to the indentation damage. Through theoretical analysis and experimental measurements, it is shown that the elasticity degradation can be mainly attributed to the anisotropic damage caused by the shear deformation in the indentation test.