The Research Of Mechanical Properties For The Surface Modification Layer With Indentation Method And Experiment

Constructing a surface modification layer(SML)is the core of anti-fatigue manufacturing technology.Characterization and measurement of the mechanical properties of SMLs are the foundation of anti-fatigue manufacturing technology.The indentation methods adopted in the commercial equipment are based on the solutions of classical contact problems for isotropic homogeneous materials.They are inappropriate for the measurement of SMLs with depth-wise inhomogeneous properties.In this thesis,inverse analysis of mechanical properties with different shapes of indenter based on the contact theory of inhomogeneous materials is developed for testing and characterizing the mechanical properties of 18CrNiMo7-6 after carburizing heat treatment.The main contributions of this thesis are as follows:(1)Methods of measuring the elastic modulus of SMLs with different shapes of indenter(spherical indenter,conical indenter,flat indenter)were proposed based on the gradient material contact theory,which was verified by finite element analysis.(2)The elastic modulus of 18CrNiMo7-6 steel alloy after carburizing heat treatment was determined by the proposed measurement method with a spherical indenter.The elastic modulus tested by the proposed method with gradient contact theory was validated by the Vickers indentation method which was performed on the cross section and top surface of samples under different loads.(3)Empirical formulas for the hardness of SMLs were obtained for the test on the top surface and the cross section,respectively.The formulas can be used to evaluate the hardness under different depths.