| Anti-fatigue manufacturing is an advanced manufacturing technology that controls surface integrity,uses fatigue performance as the main criterion and improves fatigue strength.It is different from the currently used "forming" manufacturing.The key point of anti-fatigue manufacturing technology is to build surface-modified layer(SML).The measurement of the mechanical properties of the SML is of great significance to the development of anti-fatigue manufacturing.The mechanical properties and raw materials of the surface-modified layer formed after heat treatment and forging are different.In this paper,a characterization method for analyzing the anisotropic elastic-plastic properties of the SML was proposed,which is based on the cut-off indentation test and inversion analysis.We performed indentation characterization and testing on the anisotropic elastic-plastic properties of the 18 Cr Ni Mo7-6 alloy steel after heat treatment.The main contents are as follows:(1)An indentation method is proposed to characterize the anisotropic elastic modulus of the SML.Based on the existing analytical solution of the contact problem between conical indenter and transversely isotropic material,we used the finite element method(FEM)to verify that it can replace the applicability of the analysis of contact problem between pyramid indenter and transversely isotropic material,and introduced the correction coefficient.With the existing instruments and equipments,we proposed the indentation characterization method for the elastic modulus of transversely isotropic materials.The indentation test was carried out on the SML with different depths after peeling,and the indentation modulus in the isotropic and anisotropic surface of the SML was obtained.Through the inversion analysis,the elastic modulus in the longitudinal and vertical directions of the surface modified layer was given,and the characterization method of the anisotropic elastic modulus of the SML was established.Finally,the elastic modulus of the SML of 18 Cr Ni Mo7-6 alloy steel after heat treatment was characterized by the method proposed in this paper.(2)An evaluation method of plastic parameters(yield strength,hardening exponent and yield strength ratio)of transversely isotropic material after delamination treatment was proposed based on indentation method.For the indentation contact model of transversely isotropic materials,we used the FEM to analyze effects of plastic parameters on the indentation response.Based on the sensitivity analysis,we established dimensionless functions to analyze the yield strength,hardening exponent and yield strength ratio.We peeled the SML and carried out indentation test on the SML with different depths.Then,according to the indentation response,using the established dimensionless functions to invert the plastic parameters of the SML,we can obtain the yield strength,hardening exponent and yield strength ratio of different depths of the SML.A method for characterizing the anisotropic plastic parameters of the SML was established.Finally,the SML of 18 Cr Ni Mo7-6 alloy steel after heat treatment was also characterized. |
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