13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- In this paper the calculation model is a double board lap connected by high strength bolt with tension load impacting on the axis of it. The joints has a top and a bottom board and one middle connection plate And thickness of joining board is 12 mm &Q345q steel, the connecting slab is 24 mm. the magnitude of bolt is 10.9 specification.&M20. Friction type aperture of the high strength bolts is 1.5~2mm more than bolt stem nominal diameter .During the calculation process bolt aperture takes 22 mm. In the process of computation, steel plate and bolts are assumed for isotropic elastic material, characteristic parameters of material see table 1. For material fatigue properties, there are many scientific research data as a reference, material fatigue properties in this paper using literature [5], [6] research data. Table 1 Material parameter table Member 2 ( ) ENmm− g 3 ( ) kg m ρ − g μ 2 ( ) yf N mm− g 1 ( ) Cα − o Gusset plate 201 7850 0.3 420 1.4e-7 Connected plate 201 7850 0.3 420 1.4e-7 High-strength bolts 206 7850 0.3 942 1.4e-7 3.2 Unit selection and boundary conditions Because screw, nut, washer are the same material, in order to reduce the contact surface analysis and unit number to increase the simulation efficiency ,the bolt model ignored the contact among screw, nut and washer ,built whole bolt. This paper we simulated high strength bolt and ignored the impact of tightening the nut on the bolt lever torque. The cell division of the finite element model is shown in Figure 1. The model is divided into seven entities part by regular hexahedron unit . the Meshing number is 1333 unit. Bolts and nuts adopted bound connection contact , reaction in the form of a confrontation between two binding contact area designated as the two roles are equal and opposing. Nut with connecting plate and connected to the backplane, connected to the base plate and connecting plate using frictional contact, this contact before the relative sliding can assume a certain level of shear stress in the two contact surfaces. Freedom at one end of the adapter plate, the intermediate connecting both DON stress is applied at one end of the freedom of the upper and lower splicing plates fixed constraints. The simulation consider different temperatures, temperature load is applied at the same time. Fig 1 3D Single lap connecting slab model Fig 2 Boundary condition and the load finite element grid partition Different friction coefficients were chosen 0.35,0.40,0.55, many studies were studied for the effects of temperature, this taking into account the temperature difference between the bridge actual working environment, respectively, of -45 a working temperature of -25, 0, 25, 45, etc., fatigue performance simulation. 4 Results analysis
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