STUDY ON SIMPLIFIED CHARACTERIZATION FORM OF LOCAL WIDE AND SHALLOW CORROSION PITS

In order to evaluate the reasonable simplified form of local wide and shallow corrosion pits on 24 steel specimens,two commonly used simplified characterization methods of semi⁃ellipsoid and spherical cap shape were selected respectively.Firstly,the calculation formulas for the volume of corrosion pits and the curvature radius of the profile of the cross section were derived.Then,the test errors of electrochemical accelerated corrosion were analyzed,and the uniaxial tension finite element analysis results of four typical steel specimens with corrosion pits were compared with their actual fatigue fracture situations.The results show that under a certain power on time,compared with the predetermined rust volume calculated by Faraday′s law,the maximum deviation of the semi⁃ellipsoidal corrosion pits′volume obtained from the measured sizes of corrosion pits reaches 53.2%,with an average deviation of 20.26%,while the maximum deviation of the spherical cap shaped corrosion pits′volume is only 32.3%,with an average deviation of 12.8%.The maximum stress points of the semi⁃ellipsoidal corrosion pits are located at the edge of the top,while the maximum stress points of the spherical cap shaped corrosion pits are mostly located at the bottom.Only when the ratio of depth to radius is larger,it is located on the trisection point of the connecting line between the bottom and the top,near the pit mouth.The danger areas indicated by the spherical cap shaped corrosion pits are in better agreement with the initiation positions of the main cracks in the fatigue fracture process of the specimens.Under two simplified forms,the differences between the pits corrosion volume and the curvature radius of the cross section profile on the specimens increase with the decrease of the ratio of depth to radius,and the relative deviation of the latter can be more than 90%,which is the main reason for the larger differences in the stress distribution.