| In recent years,with the continuous popularization of the assembly building,high-strength bolted joints have been more and more widely used in the steel structure.High-strength bolted joints have the advantages of easy installation and high construction efficiency in the actual project.But in the steel structure directly bearing the dynamic load(steel structure bridge,space structure with suspension crane,elevator shaft in steel frame structure and steel structure tower with wind turbine),the high-strength bolted joints are often used in a large scale.In this paper,M20 torsional shear high-strength bolts as the object of study,the main study in the eccentric tension of the amplitude of fatigue performance,respectively,the use of experimental research and finite element simulation methods,the main work and conclusions are as follows:1.With the help of the AMSLER fatigue testing machine of Switzerland,the variable amplitude fatigue tests of 10 groups of M20 torsional shear high strength bolts under eccentric tension were completed.The loading regime was "low → high".The variable amplitude fatigue test results were converted into the equivalent constant amplitude fatigue test results,and the S-N curves and logarithmic curves with the equivalent stress amplitude parameters were plotted.The allowable stress amplitude of 2 × 106 cycles was calculated,which was slightly higher than the equivalent stress amplitude of constant amplitude fatigue.2.ABAQUS finite element software is used to analyze the stress distribution of high-strength bolts,single high-strength bolt,H-shaped steel beam end plate and intermediate short column,and the stress variation curves of each key part with external load are drawn.Based on the eccentric state of the high-strength bolts,the stress variation law with external load is obtained.Then the influence of the diameter of the high-strength bolts(M20,M24,and M30)and the wall thickness of the intermediate short column(10mm,12 mm and 18 mm,respectively)on the stress of each part of the high-strength bolts is analyzed by changing the diameter of the high-strength bolts(M20,M24,and M30)and the wall thickness of the intermediate short column(10mm,12 mm,and 18mm).3.The fatigue fracture mechanism of M20 high strength bolts was investigated by macroscopic and microscopic methods based on the analysis of 8 groups of test results.The results of fracture analysis show that the fatigue fracture of M20 torsional shear high strength bolts has typical fracture characteristics,that is,the fracture location of high strength bolts is located at the first screw tooth.The results of high power SEM showed that the crack origin and extension of high strength bolts were complicated,the texture trend was obvious and the dimple holes were obvious.The fractures can be divided into two types: the first type is fast fracture(5 groups in total)at high stress amplitude loading and the second type is stable fracture(3 groups in total)at low stress amplitude loading cycle.High-strength bolts with stable fracture type have good toughness,large crack propagation area and sufficient crack development.4.The fatigue life of M20 torsional shear high strength bolts is estimated by the cumulative damage rule.The results show that the D values calculated by the two rules are all dependent on the chosen constant amplitude fatigue life calculation formula.Although the Cortan-Dolan rule makes up the shortcoming that the Miner rule is not sensitive to the stress amplitude loading level,it is more accurate to estimate the variable amplitude fatigue life of the high strength bolts with large stress amplitude.Because the stress amplitude of the test in this paper varies greatly,the Miner rule is more reasonable to estimate the variable amplitude fatigue life of the test. |
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