Analysis Of Stress Concentration With Bolt-Sphere Joints

Bolt sphere space Grid is a new kind of structure. As a joint, bolt-sphere joint is used for transferring three-dimensional flow in space grid or shell grid. It directly affects the quality of the installation of the grid. Similarly, fatigue of bolt-sphere joints is a major problem of the bolt sphere space grid, the critical of which is fatigue of high strength bolt. Stress concentration is a major problem of high strength bolt which always fracture because of fatigue.Firstly, the mechanism of metal fracture, fatigue factors of high-strength bolts were summarized systematically in the paper. Then finite element analysis software is used for creating models of bolt-sphere joins for stress concentration analyzing .The paper including the following contents:(1). Creating models of 15 kinds of high-strength,analysed bolts root stress of bolt thread from single gap to multi-gap, the first bolt transition the maximum fillet stress; different stress concentration coefficient is obtained ,which concerned with different number of thread teeth and different diameter, stress distribution under multi-threaded teeth was obtained; the formulae of stress concentration coefficient including single gap and multi-gap are concluded which changes with d/d_r(d_r is diameter of bottom of screw-thread, d is diameter of bolt);(2). Through matching M22, M27, M30, M39 with Bolt Sphere of eight different diameter bolts , the effect of bolt-sphere joggle joint's optimize combination on stress distribution was analyzed;(3).Studying the effect of detail size of sealing-plate on load-bearing capacity of joints;(4).Discussing the impact of different bolt shape with stress concentrate;(5).Based on the above, measures which can improve fatigue behavior of Bolt Sphere Space Grid were given.Through the study of the paper, it will provide some references respect to joins reasonable design , improve fatigue strength of space grid and degree of security.