| China as a "grid power" country, the high speed of its development, thewide range of application both claim the top spot in the world. Grid structurewith bolt spherical joints, that is convenient, fast and easily disassembled toconstruction and other characteristics, has been widely used and comes to thefirst among so many forms of the grid structural joint.The study on the fatigue performance of bolted spherical space grid undersuspended crane is a hot issue which is urgently to be solved in academia andengineering at home and abroad. And the key to space grid with bolt sphericaljoints is the fatigue problem of high strength bolt at hanging point. In thispaper, the high strength bolts of bolted sphere space grid as the research object,the following research work is carrying out.(1) By using3D3S and Midas structure design and analysis softwares tomodel the overall bolt sphere space grid structure under the action of suspendedcrane. For the stress amplitude of the members which are near the hangingpoints when there is a suspended crane or not is obvious, the fatigue problem isprominent. So designing a trajectory of the crane, it studies the cycle index ofsome members in every stress amplitude level. Then find out effective stress amplitude, verify the safety of the space grid using the fatigue test in the designreference period. Calculated the fatigue life through crack propagation theory,the hanging points are proved to be safe in the design reference period.(2) Through the fatigue tests of the high strength bolts of bolted spherespace grid, it obtained that constant amplitude fatigue test data of three M3940Cr high strength bolts, and the shortest life of the bolt is more than thecorresponding members of the proposed space grid structure. So it is consideredthat the space grid is safe in the design reference period. At the same time, itcarried out that the macro and micro analysis of the fatigue fracture of the boltby electron microscope, studied the failure mechanism of the bolt, and alsoutilized crack propagation theory to estimate the life of bolt.(3) Using ABAQUS finite element software to theoretically analyze thehigh strength bolts of bolted sphere space grid, it obtained that the stressconcentration coefficient decreased with the increase of the radius of thread atthe end of the transition arc under axial tension, and within specification limits,it generally has the linear relationship. Meanwhile, the stress concentrationcoefficient of first trend towards smaller trend with the increase of the numberof exposed thread, and this trend gradually slow down. It can be considered that"false twist" is weakened to static strength of bolts, but has little effect onfatigue strength. In addition, the metallographic analysis on M27and M39highstrength bolts further confirmed the hardenability of core cannot exist in largediameter high strength bolts, and put forward measures to improve the fatiguestrength of high strength bolts, especially for large diameter high strength bolts.Through the analysis of this research, it not only will provide someexperimental and theoretical bases to fill deficiencies and blanks of the fatiguecalculation regulations for space grid structure, but also further promote thewide application of space grid structure with suspended crane in industrialplants. |
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