| In actual engineering,some steel structures have been in the offshore environment for a long time,and corrosion fatigue occurs under alternating loads such as wind loads and waves,which seriously reduce the safety,durability and reliability of steel structural members and buildings.Q345 B steel is widely used in steel structures,but there are few research data on corrosion fatigue characteristics.The main research contents of this paper based on Q345 B steel are as follows:(1)Based on the dry-wet ratio of Qingdao marine environment,the salt spray test corrosion conditions were designed.The corrosion rate of the corrosion test specimens was calculated and the salt spray accelerated corrosion kinetics model was fitted.The salt spray test accelerated corrosion is 25.6 times of the normal atmospheric exposure test corrosion rate,achieving a better acceleration effect.(2)Through the indoor normal temperature tensile test,the ultimate strength and yield strength of the Q345 B steel after corrosion decreased significantly,and the yielding platform in the steel constitutive curve gradually shortened.Based on the Shi Yongjiu model,the parameter ? was introduced to modify the constitutive relationship model of the steel after corrosion,and the correction results were in good agreement with the experimental data.(3)Through the fatigue test,the fatigue life curve(S-N curve)of Q345 B steel at different corrosion rates was obtained to characterize the fatigue characteristics of steel,and the influence of corrosion rate and stress ratio on the fatigue life of steel was studied.As the corrosion rate increases,the fatigue life of steel decreases sharply;when the stress ratio increases,the fatigue life of steel increases.The graphs are drawn according to the fatigue life and corrosion rate corresponding to different stress amplitudes,and the different corrosion rate intervals are divided into three stages.(4)Because the fatigue test has large discreteness and long period,it is necessary to measure the complete fatigue S-N curve time and economic consumption of different materials.This paper introduces the gray system theory to process small sample data and establish a GM(1,1)model,which can accurately predict the steel S-N curve through limited test data.The GM(1,1)prediction model is used to correct the tail residual error,which makes up for the defect that the error of the prediction model tail segment is getting larger and larger.(5)Through the fatigue crack propagation test,based on the Paris formula,two parameters of the data are used to fit the parameters C and m of the Paris formula of Q345 B steel.The influence of corrosion and thickness on the fatigue crack growth rate of steel was studied. |
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