Molecular Dynamics Study On Fatigue Cracks Of Nickel Metal Under Hyper-Gravity And Cyclic Loading

Nickel-based superalloys are widely used in the aerospace field and are the main raw materials for turbine blades.In actual working conditions,their mechanical properties are affected by cyclic loads and hypergravity environments and are quite different from static mechanical properties.In this paper,the molecular dynamics method is used,and the supergravity load is introduced innovatively,and the evolution process of the fatigue crack of metallic nickel is studied.The specific research contents are as follows:Firstly,the fatigue crack growth behavior of the single crystal nickel [001](010)crack model in the hypergravity environment was simulated at 1 K,300 K,600 K and900 K.By applying different magnitudes of hypergravity strength to the model,namely 1? 1012 g,3? 1012 g,6? 1012 g and 8? 1012 g,it was found that the greater the supergravity strength,the greater the stress gradient generated by the crack model,resulting in a rapid decrease in fatigue life.The model transitions from brittleness to ductility at temperatures from 1 K to 300 K,with brittle fracture at low temperature,and the crack propagation mechanism at high temperature changes to passivation effect and pore nucleation,accompanied by a large number of dislocations and slip bands.produce.In addition,the critical stress intensity factor is greatly affected by the supergravity intensity and temperature.The higher the temperature,the greater the supergravity intensity,and the lower the critical stress intensity factor.Secondly,the deformation mechanism of the crack model near the tip and the evolution process of the internal microstructure under different supergravity strengths at room temperature are analyzed.It is found that different loading directions lead to different propagation mechanisms of the crack model.The crack tip will form a symmetrical dislocation line,and it will move near the tip for a long time,which relieves the stress concentration and increases the crack growth rate slowly.The propagation mechanism of cracks at room temperature is passivation effect,and the increase of supergravity strength will lead to the advance of the time when the tip emits the plastic slip band.Finally,the uniaxial stretching of polycrystalline nickel under hypergravity load was simulated,and it was found that the slip bands and dislocations generated by polycrystalline nickel cracks grew within a single grain,and when they grew to the grain boundary,they would stop expanding due to the resistance of the grain boundary.,which in turn emits slip bands from the remaining grain boundaries to relieve stress.The main crack expands through the cleavage mechanism,and the pores grow along the grain boundary and combine with the main crack to cause fracture;the super-gravity strength will make the expansion path of the grain boundary inclined to the tensile stress region.In this paper,the dynamic evolution process of metal nickel fatigue cracks in a hypergravity environment is simulated,and the effects of temperature,loading direction,and the interaction between grain boundaries and hypergravity on the fatigue crack propagation mechanism are discussed.The understanding of the evolution mechanism has laid a theoretical foundation for studying the service performance of materials in the hypergravity environment.