| 304 stainless steel is an important manufacturing material in modern industry due to its good comprehensive properties.The service life of components made of 304 stainless steel under alternating loads is closely related to the high-cycle fatigue performance of the material.In addition,defects such as holes and inclusions are inevitable in the production or use of components,and the existence of these defects directly affects the service life of the components.To address these issues,this paper uses the crystal plasticity fini te element method to evaluate the fatigue life of 304 stainless steel.The main research contents and conclusions are as follows:(1)A polycrystal model reflecting the microstructure of 304 stainless steel is established using the Voronoi diagram method.The effects of grain quantity and mesh quantity on the calculation results of the polycrystal model are analyzed.Uniaxial tension simulation is conducted to obtain the stress-strain curve.By continuously adjusting the parameters until the simulated curve closely matched the experimental curve,the parameters of the crystal plasticity constitutive model are finally determined.(2)The S-N curve of the material is obtained by conducting fatigue tests on 304 stainless steel specimens using the up-and-down method.The polycrystal model of 304 stainless steel is subjected to cyclic loads with different stress amplitudes,and the micro stress field and micro deformation distribution under different fatigue loads are analyzed.The fatigue crack initiation life of 304 stainless steel under different stress amplitudes is studied.The fatigue life of304 stainless steel is predicted based on the accumulated plastic strain fatigue indicator parameter.The results show that with the increase of stress amplitude,the cumulative plastic strain of the polycrystal model of 304 stainless steel under the same cycle increases,and the fatigue crack initiation life decreases significantly.The predicted results of the fatigue indicator parameter based on accumulated plastic strain are in good agreement with the experimental results.(3)A polycrystal model with a pore or an inclusion is established,and the micro stress field and micro plastic deformation distribution of two defects under cyclic loads are analyzed.The influence of two defects on the fatigue crack initiation life of 304 stainless steel is studied.The results show that defects are prone to cause stress concentration,and the accumulated plastic strain near a pore is significantly higher than that of an inclusion.(4)The influence of the size of different types of defects on the fatigue crack initiation life of 304 stainless steel is studied by applying the same cyclic load to polycrystal models with different pore sizes or inclusion sizes.The results show that with the increase of pore size,the influence on the fatigue crack initiation life becomes greater,but when the pore size increases to a certain extent,the influence on the fatigue crack initiation life is no longer obvious.The size of the inclusion has a great influence on the fatigue life,and inclusions with smaller size have longer fatigue crack initiation life. |
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