Study On Fatigue Crack Blunting Of Nano-twin Materials

Due to its special microstructure,nanocrystalline materials exhibit excellent properties such as high strength,high hardness,and high electrical conductivity.However,experimental data shows that when the grain size of nanocrystalline copper is reduced,its strength is increased,along with a decrease in plasticity,and when the grain size of nanocrystalline copper is reduced,its strength is increased,and plasticity is not lost..At the same time,the twin scattering ability of the twin boundaries is very small,which means that the introduction of a large number of twin boundaries can not only increase the material strength but also not affect the conductivity of the material.This provides us with important clues for further study of nanocrystalline materials.In this paper,on the basis of fully understanding the mechanical behavior and deformation mechanism of nanocrystalline materials,we discussed the distribution of dislocations near the crystal crack tip,studied the effect of grain size on the crack blunting,and constructed nanocrystalline twin fatigue.The model of the dislocations at the crack tip is discussed.The influence of the dislocation emission on the crack blunting of the twinning material is discussed.The key issues studied and the progress achieved are as follows:(1)We theoretically show that for the grain size models of nanocrystals and ultrafine crystals at room temperature,the cracks are highly sensitive to blunting caused by lattice dislocation emission,especially the grain boundary acting at the crack tip at the same time.Dislocation emission and the resulting blunt of nanometals.When the nanocrystal grain size decreases,the material tends to exhibit brittle behavior(2)Based on continuous dislocation theory,we study the distribution of stress and dislocation near the single crystal crack tip.It is generally believed that dislocations nucleate directly at the crack tip.However,in the case of shear stress,not only at the crack tip,but also dislocations must appear at the same time.In the field of dislocation nucleation.(3)Based on the mechanism of crack initiation and energy analysis,we established a twin-boundary dislocation emission model,studied the growth conditions of blunting cracks and the blunting dislocation emission,compared with the previous experimental data,and analyzed the rationality of the model.