Study On The Influence Of Surface Roughness On Fatigue Life Of Aluminum Alloy

Fatigue damage on the surface of parts is usually caused by surface defects and stress concentration from surface topography during the manufacturing process.The fatigue strength of engineering components increases with the decrease of surface roughness.This article will study the effect of surface roughness on the fatigue life of aluminum alloy from the perspective of surface stress concentration.The main research contents of this paper were as follows:?1?The influence of surface micro-notch characteristics on the stress concentration coefficient was studied by simulation.Simplify the surface roughness into a series of elliptical micro-notches.The depth of the dents b is between 1 and 12?m.The width-depth ratio a/b is between 2 and 10,and the spacing between the multi-notches center d is between2?10 notches width a.The effects of the single and multiple micro-notch parameters on the stress concentration coefficient were studied separately,and the relationship between the stress concentration coefficient and the micro-notch parameters was established for data fitting.Several groups of micro-notch parameters were randomly selected for simulation analysis,and the simulation results were compared with the fitted values.The maximum errors of single micro-notch and multi-micro-notch were 1.41%and-4.35%,respectively,illustrating the validity of the established relationship.?2?Research on micro-notch parameters and mathematical definition of related surface roughness parameters,R_z,S,R_smwere selected to convert the micro-notch parameters,and then the relationship between the surface roughness parameter and the stress concentration factor were established.?3?Four different surface roughness specimens were fabricated,and model reconstruction based on real surface topography through microscope observation were completed,stitching,calibration,edge extraction,etc.Then,the stress concentration factor was compared between FEM analysis and numeric.Results showed that the maximum error between the two was only 1.25%,indicating that the simplified notch model can effectively reflect the true stress concentration of the test piece.At the same time,fatigue tests were carried out to obtain the fatigue life corresponding to different surface roughness test pieces.The results showed that the smaller the surface roughness,the larger the fatigue life value of the test piece.?4?With the stress concentration factor as the intermediate parameter,the relationship between surface roughness and fatigue life was established through the estimation of basic parameters.At the same time,the fatigue test results were compared with the prediction results.It was found that the change trends of the two were basically the same,and the maximum error was-15.65%.It further explained that the fatigue life prediction was simplified by simplifying the surface roughness into a gap model and establishing the corresponding relationship was reasonable and effective.