The Test On Constant Amplitude Fatigue Behavior Of Space Grid Structure With Crossed Plate-Welded Hollw Spherical Joints

With increasing amount of the steel and the expansion of Steel structures’ application, the grid structure is widely used in large public and industrial buildings. Due to wildly application of Suspension crane in industry, the fatigue problem of grid structure is becoming a major problem in industrial and academic area. The behaviour of grid structure joints is complex, and stress concentration is obviously, the fatigue problem became the major content in the fatigue problem of grid structure. Because the research are not systemic in fatigue problem, technicians’structural of fatigue design is without theoretical base. The fatigue testing is the most effective research method. The thesis takes the crossing board-welding air ball joints(which is wildly used in grid structure) as the research object, the research content includes:1. Using the ANSYS software, analyzing the crossing board-welding air ball joints by fnite element method (FEM), under the action of axial force, understand the stress distribution of the crossing board-welding air ball joints, and calculate the stress concentration coefficient of the board-ball joints.2. Do the static fatigue experiment about the crossing board-welding air ball joints, collect the strain in every measuring point, and get the values for the stresses in every measuring point. Contrasting the stress concentration coefficient from the experimental data with the theoretical values, and analyzing the reason of error.3. According to the fatigue experiment about the crossing board-welding air ball joints, we get observed fatigue test values. Through regression between this experimental data and experimental data which we’ve got, we get fatigue S-N curve which is more perfect. At last, founding fatigue design method which takes the nominal stress range as the basic parameter.4. Using the magnifier and electron microscope, the fatigue fracture is analyzed from macroscopic and microscopic aspects, studying the fatigue failure mechanism of crossing board-welding air ball joints. According to the analysis about the factor which influences the broken of the crossing board-welding air ball joints, we sum up the effective measures which can enhance the fatigue strength.