Analysis Of Stress Concentration Factor And Relative Stress Gradient Of Surface Topography

The failure type of high-end mechanical parts is often the fatigue failure which is not easy to detect.Areas with large changes in the surface topography of parts can not avoid the phenomenon of local increase in stress during service,and these areas become a high incidence of parts failure.Therefore,it is very important to study the stress distribution of surface topography.From the perspective of stress concentration and stress gradient,this paper analyzes the surface topography of round bar samples with different stress concentration factors(SCFs),mainly including the following research contents:(1)Machined the round bar sample of K_t=1,and measured the main size,shape and position tolerance,and surface topography in sequence.The surface evaluation of the round bar sample for fatigue evaluation was made against fatigue.For the surface topography of the measured sample,noise reduction was carried out according to the Murakami model,data was filled for the unmeasured area,and the topography of the round bar surface was fitted to the topography on the plane and surface topography was reconstructed.The perturbation method was used to analyze the three-dimensional surface topography.The empirical formula of Sa,Sz and average SCF,average relative stress gradient(RSG)were given.The joint probability density function of SCF and RSG was obtained.In addition,the distribution of the stress field of the gradient structure is solved by the proper generalized decomposition method,which provides a theoretical basis for the further study of the problem of stress concentration on the rough surface of gradient structure.(2)The finite element model of the notched specimen with surface topography was established to reconstruct the three-dimensional surface topography.A finite element method(FEM)for calculating the SCF and RSG of the round bar specimen is presented and compared with the perturbation method.The FEM of surface topography was applied to solve the SCF and RSG of the surface topography of notched samples at K_t=2.Based on the surface topography of sample K_t=1 and notched sample K_t=2,the surface topography with different surface roughness was simulated by FEM,and the required minimum mesh size was obtained,which provided a reference for the sample spacing required for the actual measurement of surface topography.