| Pinned connections are widely used in various spatial structures as an ideal form of hinge connection.Whether the stress state of joints could meet the requirements of strength and stiffness is the key to the mechanical performance of the space structure.Fatigue failure of the bolt pin in pinned connections in the large-span steel structure may happen under reciprocating dynamic loading,causing a great threat to the overall reliability and safety of the structure.The relevant domestic and foreign regulations and research for pinned connection are mostly limited to structural design requirements and static bearing performance.However,there is still a lack of adequate explanations and reports on its fatigue strength and failure characteristics under reciprocating dynamic loading.Therefore,jointly funded by the National Natural Science Foundation of China(No.51708384),Shanxi Province Overseas Researchers’Science,and Technology Activities Funding Project(No.DC1900000602)and Shanxi Basic Research Youth Fund Project(No.201901D211017),this paper took the M36bolt pins in pinned connection as the research object and discussed the constant amplitude fatigue performance and the influence of related factors through experimental research and numerical simulation methods.The main research contents and relevant conclusions are as follows:(1)The static tensile tests of 3 specimens of bolt pins and the hardness tests of 6specimens were carried out.The mechanical performance parameters of the batch of specimens were obtained;(2)A reasonable fatigue loading device was designed and a scientific constant-amplitude fatigue test program was formulated.Based on these,the constant-amplitude fatigue tests of 9specimens of M36 bolt pin in pinned connection were carried out.According to the loading parameters of the test and the corresponding fatigue cycles,the S-N curve of the bolt pin specimens under constant-amplitude fatigue loading was fitted and the fatigue life estimation formulas under constant amplitude were obtained.The corresponding nominal fatigue strength at 2×10~6 cycles is 42.39Mpa,which were 84.79%and 42.39%of the recommended values of allowable fatigue strength of component Z11 and J2,respectively,namely the axial-tensile fatigue and shear fatigue of normal bolts stipulated in Chinese national standard for the design of steel structures;(3)The fractures of the 9 bolt pin specimens all showed typical fatigue failure characteristics.Through the macro and micro analysis of the fatigue fracture of two typical specimens,the constant-amplitude fatigue failure mechanism of the bolt pin was revealed.The fracture positions of the 9 specimens were summarized and classified to analyze the force characteristics of each area when the bolt pin was subjected to reciprocating loading along the axis of the ear plate;(4)The finite element analysis software ABAQUS was used to analyze the stress condition of the specimen under the elastic state when subjected to the static loading along the axial direction of the ear plate.The stress distribution and stress concentration position of the surface of the specimen under static force were obtained;(5)n Code Designlife software was used to simulate the fatigue performance of the bolt pins in pinned connection.The experimental group of fatigue simulations and the control group of the fatigue tests were established referring to the loading program of the constant-amplitude fatigue tests.The corresponding nominal fatigue strength of the bolt pin under fatigue simulation at 2×10~6 cycles is 39.73Mpa,which is 93.7%of the corresponding value of the test.The reliability of the simulation method was verified;(6)The fatigue numerical simulation parametric analysis of 32 models with 4 factors of the bolt pin was carried out based on this reliable fatigue simulation method.Through the univariate analysis,it is found that the constant-amplitude fatigue performance of the bolt pin is positively correlated with two parameters of the loading stress ratio and the bolt diameter,negatively correlated with the initial growth of the pin hole clearance,and substantially independent of the spacing between the ear plates.The most unfavorable position for the fatigue of the bolt pin is the compression area between the pin-holes of the inner and outer ear plates and the surface of the bolt pin.Besides,the fatigue damage in the tensile area in the middle of the bolt pin is more likely to happen with the increase of pin-hole clearance,the ear plate spacing,or the decrease of the diameter of the bolt pin.Through orthogonal analysis,it is found that the ranking of the sensitivity of the factors affecting the constant-amplitude fatigue performance of the bolt pin is:the clearance of pin-hole→the bolt diameter→the loading stress ratio→the ear plate spacing. |
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