The Study Of Multi-Scale Analysis For Macroscopic Failure Induced By Microdefects Of Nickel-based Materials

In recnet years,cross-scale numercial as s hot topic in the field of mechanical research has attracted many researchers'attention.The failure process of materials coupling multiple scale,and the connection between scales is progressive step by step.In order to have a deep understanding of the phenomenon,we should know the different study method at different scale and connect the failure process of different scale to form a cognitive whole by means of multi-scale methods.In this paper,the multiscale was divided into electronic scale,atomic scale and macroscopic scale,and the corresponding analysis methods are the first principle method,molecular dynamics method and extended finite element method.The influence of element doping on the mechanical properties of materials is studied on the electronic scale,which provides a basis for numerical simulation at atomic and macroscopic scales.The mechanism of material deformation and defect evolution at atomic scale is studied to provide theoretical guidance for material deformation and failure behavior at macroscopic scale.At the macroscopic scale,the mechanical parameters in the process of material failure are calculated by using the extended finite element method.The first principle method based on density functional theory was used to study the formation heat and different elastic constant of Co,Ru,Re,Ta,W,Mo doped Ni3Al alloy materials under different pressure.We got the results that element dope could strength the materials,there was a possible that Ru and Re elements can be replaced partial,which would not reduce the mechanical properties obviously to achieve the purpose of lowering the cost of the development of high temperature nikel based alloy.Molecular dynamic methods was used to analysis the grain size and cooling rate to the influence of transformation temperature and phase transformation mechanism.The result shows:when the cooling rate is-5 K/ps,as the grain size decrease from 17.5nm to 8.5nm,the Martensite start temperature decrease from 230 K to 80 K,the number of nucleation point also decrease gradually and only nucleate inside the grain,the Martensite grow towards the grain boundary in the process of cooling.When the grain size decreases to 4.1nm,the transformation was suppressed.In the process of heating,the nucleation point of Austenits nucleates near the grain boundary and grows towards inside of the grain.When the cooling rate increase from-5 K/ps to-15 K/ps,the finish transformation temperature of Martensite decrease from 190 K to 20 K,the degree of grain got refined increased and also the transformation hysteresis width(A_f-M_f)decrease with the increase of cooling rate in the model with grain size of 17.5 nm.The effect of cooling rate on martensitic phase growth mechanism is relatively small.A molecular dynamics model is used to simulate the compressive loading process along different crystal orientations of nano-twinned Ni with void defect at the twin boundaries.The loading angle is defined as the angle between the loading direction and the twin boundary,loading angles of 0,15,30,45,60,75,and 90owere investigated in this study.The effects of different loading directions on the mechanical properties and the dislocation glide mechanisms were investigated.The dislocation glide process during the initial stage of plastic deformation for different loading directions was also studied.The results show that the dislocation glide mainly occurs along the{111}plane that is inclined to the twin boundaries when the loading direction is 0o.The dislocation glide process is constrained by the twin boundaries and,therefore,slips along the twin layers.As the loading angle increases from 0oto 45o,the dislocation gradually shifts and slips along the(111)slip plane that is parallel to the twin boundaries and twin migration and twinning occur.As the loading angle continues to increase to 90o,the dislocation slips along the{111}plane again during the loading process.In addition,the dislocation slips toward the adjacent twin layers because they are strongly hindered by the twin boundaries.Finally,simulated the I model crack propagation process of Ni3Al combined with Finite element method and molecular dynamic method.At the established platform from macroscopic to microscale,the stress intensity factor as the connection of mascroscopic and mesoscopic and the displacement as the connection of mesoscopic and microscopic,simulated the crack progation process.Compared with the Stress-strain curve in our results and references,we got ideal simulation results and verify the correctness of the simulation method.