| 304 stainless steel is widely used in people’s daily household items,medical appliances,ships and aviation components because of its excellent comprehensive performance and relatively affordable price.At present,many scholars have done a lot of research on 304 stainless steel fatigue,and achieved many significant results.However,there are few studies on fatigue of 304 stainless steel with different grain sizes.Therefore,this topic takes 304 stainless steel with different grain size as the research object,through fatigue experiment in many aspects to study the influence of size effect on its fatigue performance.Firstly,scanning electron microscopy(SEM)was used to observe the macroscopic and microscopic morphology of the fatigue fracture at different magnification times,and the influence of grain size on the fatigue fracture morphology was analyzed.Secondly,the finite element software and fatigue life calculation software were used to simulate the fatigue life of stainless steel specimens with different grain sizes to analyze the feasibility of the simulation and the influence of grain size on the simulation results.Finally,the fatigue lives of fatigue specimens with different grain sizes were predicted under different reliability because of the dispersive fatigue lives under the same stress level.The main research contents and conclusions of this paper are as follows:(1)In view of the long cycle and high cost of high cycle fatigue test and the influence of grain size change on the simulation results,etc.By using Abaqus and Fe-safe software,finite element simulation of 304 stainless steel fatigue specimen life with different grain sizes is carried out.The simulation results can replace the experimental results,which can greatly shorten the experimental period and reduce the experimental cost.The results show that the sample with large grain size needs more mesh than that with small grain size,and the precision of the simulation results of large grain size is smaller than that of small grain size.The results show that the number of mesh in the fatigue specimen with the same grain size is more than that in the condition of high stress than low stress.(2)Aiming at the problems of dispersive fatigue life and small number of specimens in high-cycle fatigue under the same stress level,an improved gray estimation method was proposed to estimate the parameters of Weibull model.The fatigue data of this test which conforms to Weibull distribution at the same stress level are brought in for verification analysis,and it is concluded that the accuracy of Weibull model parameter estimation using the improved method is higher than that using the gray estimation method alone in a small sample size.(3)The observation and analysis of the fatigue fracture morphology of 304 stainless steel specimens with different grain sizes show that the fatigue specimens with different grains have the same macro fracture morphology.The difference is that with the increase of the fatigue life cycle,the proportion of the crack growth zone in the whole fracture area will increase.Through the observation and analysis of the fatigue fracture morphology of stainless steel specimens with different grain sizes,it is concluded that the change of grain size has an obvious effect on the morphology of crack source region,crack growth region and transient fracture region.By observing and analyzing the fatigue fracture morphology of the same structural specimens,it is concluded that the change of stress level also has an obvious influence on the micro-fracture morphology of the above three areas. |
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