Testing And Characterization Of The Elastic-plastic Properties Of Surface-modified Layers

Advanced mechanical equipment is the leader in the machinery industry and occupy the core position of the manufacturing industry.The service life of key components is an important indicator to measure the advanced degree of advanced mechanical equipment.The fatigue life of key components can be greatly improve thought the Anti-fatigue manufacturing technology and its essence is to construct the surface-modified layers.Heat treatment,shot peening,water jet,rolling and other strengthening means can produce surface-modified layer on key components.The characterization and testing of the mechanical properties of the surface-modified layer is of great significance for the research of anti-fatigue manufacturing of key components.In this paper,the elastoplastic properties of the mechanical properties of the carburized heat-treated 18CrNiMo7-6 alloy steel surface-modified layer were studied by stripping sheet tensile test and the reverse analysis of indentation.The main research contents are as follows:(1)A test method for obtaining the elastoplastic properties of the surface-modified layer by stripping sheet tensile test was given.The traditional tensile test was carried out on the thin-layer tensile specimens and the stress-strain curve of the thin layer sample of the surface-modified layer was obtained,and the elastic modulus,yield strength and strain hardening exponent of the surface-modified layer were analyzed.By using the method,the mechanical properties of the surface-modified layer of 18CrNiMo7-6 alloy steel with carburizing heat treatment were obtained,and the empirical formula of the mechanical properties of the surface-modified layer along the depth was given.(2)The finite element analysis model of the plastic properties of surface-modified layer was established.The influence of elastoplastic properties such as elastic modulus,strain hardening exponent and yield strength of surface-modified layer on indentation load-displacement was analyzed by finite element method.Thehigh throughput finite element simulation of the indentation model of different properties was carried out and the indentation load-depth curve database of the gradient material plastic properties of metal materials was established,which was the foundation of the reverse analysis method of plastic properties of surface-modified layer.(3)Combining the indentation test and the database of plastic properties analysis of the gradient material,the reverse analysis method of the plastic properties of the gradient material was established.By using the reverse analysis method proposed in this thesis,the plastic properties of the substrate material of the alloy steel18CrNiMo7-6 and the surface-modified layer of the carburized heat-treated alloy steel 18CrNiMo7-6 were analyzed and the plastic properties were also given.