Microstructure Mechanics Analysis And Brittle Fracture Mechanism Of Metal Materials

As one of the three pillars of modern civilization,material has been closely related to human life.As the main engineering structural materials,metal materials are widely used in petrochemical,aerospace,nuclear power plant and other fields.With the increasingly complex service environment of various engineering equipment,accidents caused by brittle fracture of metal materials are common.The research on brittle fracture of metal materials at home and abroad can be roughly divided into two aspects: macroscopically,fracture parameters and criteria of materials are studied by using fracture mechanics theory model,and microscopically,the microstructural and geometrical characteristics of materials and their effects on the macroscopic properties of materials are explored.However,it is difficult to explain the fundamental reasons for the deterioration of material properties only from the macro-mechanical analysis of materials.And it is difficult to clearly describe the damage process of materials by discussing the influence of macroscopic properties of materials only from the aspect of metallographic structure changes.In order to further analyze the brittle fracture mechanism of metal materials,it is necessary to combine macro-mechanical properties with micro-structural changes to predict and estimate the macro-mechanical properties of materials through micro-structural changes.According to the microstructural characteristics of austenite and pearlite in metal materials,numerical analysis models of austenite and pearlite microstructures are established respectively in this paper.And the effect of austenite grain boundary arrangement angle,grain boundary thickness,austenite grain size as well as pearlite lamellar spacing and pearlite aggregate size on the microstructural stress and strain of austenite and pearlite materials was studied by finite element method.Based on the grain boundary characteristics and the theory of non-equilibrium grain boundary segregation of solute atoms under elastic stress,the effects of micro-parameters on the macro-properties of materials are discussed,which have better consistency with the experimental results.The crack module is established in the austenite micro-model,the distribution of grain boundary tension stress around a single grain boundary crack and the stress intensity factor at crack tip under multiple grain boundary cracks calculated by using finite element method and fracture mechanics theory.The results show that when there is only one grain boundary crack,the tensile stress on the grain boundary near the crack and consistent with the direction of crack propagation will continue to increase with the crack propagation under the action of tensile stress.When multiple grain boundary cracks appear,these cracks will promote each other and grow together.According to the calculation results in this paper,the cumulative behavior of micro-damage of austenitic materials under tensile stress is discussed,and the micro-mechanism of stress corrosion cracking of austenitic stainless steel under tensile stress is described.The research results have important reference value for damage analysis of metal materials.