Study Of Hardness And Residual Stress Measurement Principles, Methods And Experiments Using Indentation Techniques Based On Energy Method

Nuclear main pump is the core component of the nuclear power equipment. Surface hardening and residual stress are important factors that affect the integrity of the surface of the pump. Thus, the development of indentation hardness and residual stress in indentation testing techniques has significant practical and academic value.Based on theoretical analysis of the indentation process, finite element simulation and experiment, we studied the effect of the indentation parameters and residual stress on indentation. In this paper, mechanical properties and residual stress was proposed in terms of using indentation techniques which are based on energy method.According to the Hertz contact theory and von Mises yield criterion, a semi-analytical model of the contact force, contact radius and contact depth was established on the basis of the finite element simulation. Based on the theory of the spherical cavity model, we established analytical model of stress, strain, and hydrostatic pressure.In addition, we analyzed the effect of material properties, the indentation parameters and residual stress on the material pile-up/sink-in. Then, a fitting function relationship between equivalent strain and pile-up/sink-in was established.Further, the elastic-plastic spherical indentation was analyzed using dimensional analysis method and the finite element simulation, the relationship among the indentation hardness, indentation work, and materials properties, indentation parameters was established, which is based on energy method and verified by experiments.Through the analysis of load-displacement curve, we detached the work of residual stress. Based on Hertz contact theory, we established a model between the indentation work and the residual stress as well. Acoording to the relationship among the dimensionless irreversible work, the equivalent strain and the residual stress, a solving method was established based on the equivalent strain and energy method.To verify the validity of the methods, we identated the typical materials by means of using the slow strain testing machine. Results showed that the accuracy meets the engineering requirements.In this paper, we proposed a theoretical and finite element analysis of the indentation response by using contact mechanics and elastic-plastic mechanics. Based on the energy method, the constraints model among the indentation response and the hardness, residual stress were established. According to this model, the hardness and residual stress can be quickly and efficiently measured. This method was proved to provide a strong assurance to the component surface integrity and residual life assessment.