| Prefabricated steel structure building has been widely used in civil and industrial buildings due to its many advantages.The beam-column end plate connection in assembly type is a common type of joint connection,and the mechanical performance of the joint is directly related to the mechanical performance of the whole structure.As the main part of end plate connection,the fatigue performance of high strength bolt is very important.In addition,considering the high strength bolt in the actual construction process,the bolt underscrew probability is high,and in the subsequent use of the pre-tightening force loss,etc.,all of the above circumstances lead to the pre-tightening force does not meet the requirements of the specification.At present,in terms of the factors affecting the fatigue performance of high strength bolts,the existing literatures have mainly studied the specifications of bolts,thread forms,loading stress amplitude and loading stress ratio,etc.,while less attention has been paid to the influence of the preloading force of high strength bolts on their fatigue performance.Supported by the National Natural Science Foundation of China(51708384),the Youth Foundation for Basic Research of Shanxi Province(201901D211017)and the Science and Technology Activities for Overseas Students of Shanxi Province(DC1900000602),this paper takes the tensile connection of 8.8-class M24 high-strength bolts with the material of 35 K as the object to conduct fatigue test research and relevant numerical simulation analysis.The main work contents and methods are as follows:1)Based on the fatigue test loading device designed by the research group,a test scheme suitable for this study was put forward.Three groups of high-strength bolts with constant amplitude fatigue tests(R=0.3/0.5/0.8)and each group of 8,a total of 24 M24 were carried out on the MTS Lankmark370.50 servo hydraulic fatigue testing machine.Under the premise of the same stress ratio R and the same stress amplitude Δσ,the constant amplitude fatigue life data obtained under different preload F were analyzed statistically,and the corresponding constant amplitude fatigue S-N curves were obtained respectively.The influence of preload on the fatigue strength of bolts was quantitatively analyzed;2)For the constant amplitude fatigue specimen,the dynamic strain gauge was used to monitor the strain change of the specimen throughout the whole process,and the strain change was indirectly verified with the MTS test specimen and reflected the change of the fatigue damage law of the bolt specimen to some extent;3)Using phenom scanning electron microscope and other instruments and equipment,the fracture morphology of 24 high strength bolts with constant amplitude fatigue in the test was photographed and recorded.The macro and micro fracture analysis(SEM)of 6 groups of bolts with complete fracture was carried out one by one,The influence of pre tightening torque interval of 100 N·m on the fracture characteristics of high strength bolt fatigue failure;4)The finite element model of bolt and loading device in line with fatigue test was established by using ABAQUS finite element analysis software.The strain size at bolt bar obtained from numerical simulation was compared with the measured value of bolt test to verify the validity of numerical simulation.The stress distribution of high strength bolts under different preload was discussed,and the influence mechanism of preload on the static and fatigue properties of high strength bolts was revealed. |
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