A Study On The Fatigue Damage Properties On The Interface Of Nanocrystalline Materials

The mechanical properties of nanocrystalline(nc)materials(strength,hardness and wear resistance)are better than coarse-grain materials due to their unique microstructure.It is known that the unique microstructure and deformation mechanism of nc materials make the crack initiation and propagation different from the conventional coarse grained materials.Here,based on a full understanding of materials crack initiation and propagation,combined of theoretical analysis and numerical simulate,the mechanical properties on the interface of ncmaterial is studied.The research contents are summarized as follows:(1)Review the research processes,effects of parameters,mechanical properties and deformation mechanism of nc and nanotwinned materials.(2)The first work is concerned with the analysis of the crack initiation on the interface of nanotwinned materials using the strain gradient theory and semi-quantitative relationship,established the theoretical model of crack initiation on the twin boundary of nanotwinned materials.Based on the strain gradient theory,weestablished the relationship between the strain and grain size on dislocation pill-up area of twin boundary,and calculated the number of dislocation pill-up on the twin boundary.A semi-quantitative relationship was established between crystallographic orientation and stacking fault energy,and derived the expression of critical crack initiation on the twin boundary based on the number of dislocation pill-up.This part mainly discussed the effect of grain size and twin lamellar thickness on crack initiation of nanotwinned materials.(3)In the second work,the I type fatigue crack propagation of nc material was studied as a theoretical model of grain size and misorientation angle,which was based on dislocation theory.This part mainly discussed the effect of grain size and misorientation angle on fatigue crack growth of nc material.(4)The established theoretical models were analyzed and discussed.The simulation results were compared with recent experimental findings,and demonstrate the established theoretical models.