Research On Fatigue Damage Characterization Based On Maximum Entropy Principle And DIC

Fatigue failure is one of the main forms of failure of industrial metal components,and fatigue failure is the most dangerous of all kinds of failure forms.Therefore,the research on the fatigue reliability of mental materials has always been the focus of mechanical,mechanical,aviation and materials researchers.Due to many uncertain factors（such as component geometry,material performance,action load,etc.）that affect metal fatigue fracture,the fracture behavior is particularly complex.As a result,it is really difficult for researchers to accurately evaluate the fatigue damage of metal materials.,For most of the traditional fatigue damage research methods,due to the complexity of fatigue problems,can only be used under specific conditions,and lack a set of general and more accurate research methods to predict fatigue damage.In order to better predict the fatigue damage and failure behavior of metal materials,An analysis method of fatigue damage evolution of metal materials is established.This method is based on the progressive damage model that combines the multilinear kinematic hardening and the Maximum Entropy Fracture Model（MEFM）,combined with the Digital Image Correlation（DIC）.Through the comparative analysis of the experimental and simulation results,the fatigue damage failure behavior of copper T2 was studied,and the effectiveness of the maximum entropy fatigue damage evolution analysis method was verified by analysis.First,two kinds of experimental samples（unilateral notch and bilateral notch specimens）were designed using copper T2 as the material,and the mechanical properties parameters of the material were obtained through the tensile section information of the unilateral notch fatigue test.During the acquisition of material parameters,digital image correlation（DIC）and inversion analysis methods are used.According to the theoretical formula of the multilinear kinematic hardening,the relevant mechanical parameters obtained by inversion are fitted into the constitutive model parameters c and^?in the MATLAB program.Based on DIC,the displacement field and strain field information of the single-sided notched specimen during the fatigue test were obtained.Combining the information of the finite element model and data from the testing machine,the displacement boundary conditions of the model and the experimental load displacement of the single-sided notched specimen Response curve were obtained.Through the trend of the hysteresis curve of the single-sided notched specimen,the change rule of the damage during the fatigue experiment was analyzed.Then,the multilinear kinematic hardening and the maximum entropy fracture model are programmed,and the non-local averaging and the cyclic jump method are used to solve the grid dependency problem and the calculation time length problem,respectively.According to the theoretical formula of the maximum entropy fracture model,it is known that the damage of the material particles is related to the cumulative plastic dissipation of the entire material.Combining with the experimental information of the single-sided notched specimen,finite element simulation analysis and inversion,the damage accumulation parameter ^k?was obtained.The experimental and simulated load-displacement response curves,the load-displacement curve under a single cycle,the field information on the characteristic points and the crack trend are compared and analyzed,which proves the accuracy of the numerical simulation of fatigue,and further illustrates the feasibility of the fatigue research method.Using the same experimental method as the one-sided notched specimen,the test load-displacement response curve of the two-sided notched specimen and the boundary conditions of the finite element model are obtained.Combining the model parameters（constitutive parameters and damage accumulation parameters）obtained during the simulation of the unilateral notch and the finite element model of the bilateral notch,the fatigue simulation of the bilateral notch specimen is completed.The bilateral notch experiment is compared with the simulation results in many ways,and the matching between the two is high,which verifies the versatility of the fatigue damage research method proposed in this thesis.Finally,the fatigue research method is applied to the field of microelectronic packaging,A failure experiment of interconnection solder joints in chip devices under cyclic loading was carried out.Based on the shear fatigue test results of the micro-connected solder joints,the same method was used to obtain the model parameters,and the applicability of the method in the micro-field was verified through the comparison between the experiment and the simulation.The research results show that the fatigue damage research method proposed in this thesis provides a new idea for the fatigue damage research and life prediction of macro metals and micro solder joint alloys.