Evaluation of indentation tensile properties of Ti alloys by considering plastic constraint effect

The uniaxial tensile properties of metallic materials can be determined by representing the indentation stress and strain by the load/depth parameters from instrumented indentation tests using a spherical indenter. Here we propose a modified algorithm for evaluating the tensile properties of Ti alloys with low E/σy values by taking into account the plastic constraint effect in low-strain regions. The ratio of elastic modulus to yield strength, E/σy, can be interpreted as a measure of the amount of deformation plastically accommodated during indentation. For low E/σy materials, deformation is elastic-dominated, so less constraint occurs than in high E/σy materials. Finite element methods and spherical indentation tests were used to explore the constraint effect for a variety of materials characterized by different E/σy. The constraint factors were plotted as (E/σy)(a/R) based on expanding cavity model. The modified approach was experimentally verified by comparing tensile properties from uniaxial tensile test and instrumented indentation tests.