Experimental Research On The Density Method Of Fatigue Damage Dependent Upon Strain Rate Of Q235 Steel

An irreversible changes have often occurred in the internal structure of the material in project,because of the cold and hot working process,the change of load and temperature,the effect by chemistry,radiation and other environmental factors.The change of the microstructure of this kind materials is manifested by the formation and development of micro voids and microcracks,not only lead to the appearance of macroscopic cracks,but also weaken the overall mechanical properties of the material,such as:the reduction of strength,stiffness and fracture toughness of the material,therefore,the structural strength is obviously weakened,and the service life is shortened.The gradual deterioration of material properties before fracture is generally called damage.A large number of facts show that materials will be damaged in the process of use,when the damage accumulated to a certain extent will cause the failure of the material.Because of the wide application of metal materials in national defense and civil industry,the research on the safety and reliability of the structure has been paid more and more attention by the domestic and foreign researchers.The research on the fatigue damage of metal has gradually become a hot research topic in the field of mechanical,chemical,textile,architecture,commodity and the other industries,shows more and more broad application prospects.The current research about the mechanical problems of fatigue damage of metal is not comprehensive,to the metal,the change of material properties with strain rate,loading frequency,stress/strain level and loading time need to be studied through the experiment of fatigue damage.On this basis,the constitutive model of metal fatigue damage which depend on the stain rate is established,and the damage degree of the member is calculated by the model,thus the remaining life of the component can be predicted.At the same time the density test method is used,to the connection of medal damage on the different strain rates and the change in internal density of material,which is of great theoretical value and practical significance for us to understand the physical properties of metals and to make rational and efficient use of metals.Therefore,the related research work not only has the important academic significance,but also has certain reference value to the engineering design department.In this paper,taking key projects of Hunan Province Department of Education deformation characteristics of microstructure,and the deformation mechanism is analyzed.Combing with the analysis of the fatigue damage and fracture in the literatures,the influence of strain rate on the internal structure of the material is studied.Through the density test method,this paper provides important experimental basis under the different stain rates of the fatigue damage about Q235 steel.At the same time,further understanding of the changes of metal microstructure mechanism and mechanical properties by optical microscopy and scanning electron microscopy,and provide a useful reference for further research and application in the future.