Research On Low Cycle Fatigue Performance Of Sealing Plate Connection In Aluminum Alloy Bolt-sphere Joints

Aluminum alloy is widely used in space grid structures because of its low density,good corrosion resistance,and high strength.However,the light gravity makes the structure more sensitive to wind load,and the fatigue property of aluminum alloy is relatively weak after the operation such as solution treatment.Therefore,under the action of fluctuating wind,the fatigue property of aluminum alloy spatial grid structures should be fully considered.In this paper,the low cycle fatigue performance of the boltsphere joints of aluminum alloy spatial grid structure is studied,which mainly includes the following four aspects:1.To investigate the cyclic hardening/softening property,hysteretic curve and fatigue life of the material,the low cycle fatigue test of 6061-T6 aluminum alloy standard specimens under 13 strain amplitude was completed.The cyclic stress-strain curves and strain-life curve of the material was obtained,which provides the material foundation for the estimation of low cycle fatigue life of sealing plate connection in aluminum alloy bolt-sphere joints.2.The low cycle fatigue test of sealing plate connection specimens with 4 specifications under five load classes was completed.The low-cycle fatigue failure mode,hysteretic curve and fatigue life of the specimens were studied considering the influence of the thickness of the sealing plate and the diameter of aluminum alloy tube.The results showed that the fracture of the specimens occurred at the junction of the sealing plate and the aluminum alloy tube,showing brittle failure.The fatigue life of the specimens increased with the increase of the thickness of the sealing plate and the diameter of the aluminum alloy tube.3.Numerical simulation of sealing plate connection specimens with 4 specifications(add 2 specifications on the basis of the experiment)is carried out using ABAQUS,and the stress and strain distribution in the elastic range is obtained.The results showed that there is a serious stress concentration at the junction of extruded and non-extruded regions in the bottom thread root of the aluminum alloy tube,which is consistent with the fracture position of the specimen in the test.The stress decreases as the thickness of the sealing plate and the diameter of the aluminum alloy tube increases.Based on the simulation results,the theoretical stress concentration factor and fatigue notch factor were calculated,and the fatigue life of the specimens was estimated by local strain approach.4.Taking K6 aluminum alloy double-layer reticulated shell structure as an example,the dynamic performance of the structure under the action of strong wind was studied using ANSYS.The vibration-load history curves of the key members were obtained,and based on the above experimental and theoretical studies,the low-cycle fatigue properties were evaluated by the local strain approach according to the obtained curves.