The Identification Of Weld Damage And Fatigue Life Caused By Wind Of The Space Truss Structure

Space truss structure is made up of welded hollow spherical joints and members,Welded hollow spherical joints are the weak links of the structure.This kind of structure which has dense frequencies includes a mass of joints and members,it is sensitive to wind load and will produce fatigue damage under wind loads.During the service period,the joints in the welds are prone to damage,The presence of joint weld damage will accelerate the fatigue failure of the space truss structure under random wind loads.In the event of sudden fatigue failure,it will inevitably cause serious damage to property and even casualties.Therefore,it is necessary to identify the degree of damage and the fatigue life of the space truss structure with welds injury.This article uses the fuzzy model recognition methods based on strain mode difference to identify the degree of damage and the fatigue life of the space truss structure.The main contents are as follows:1.Establishing fine finite element model of joint with welds injury by using ANSYS software to obtain the correspondence between the joint stiffness and the degree of weld damage,then establishing equivalent finite element model of the space truss structure with different weld damage degree by using Matrix 27 unit as equivalent unit.2.Using harmonic wave superimpose method to simulate fluctuating wind speed time history based on Davenport power spectrum,then obtain the simulated wind load of the space truss structure according to the transformational relation between the wind speed and wind pressure.3.Using local stress-strain method to estimate fatigue crack formation life of the space truss structure with different weld damage degree.First,determining the fatigue dangerous node of the structure,obtaining the local stress-strain spectrum,using the rain flow counting method to extract strain cycle of the fatigue dangerous node,then according to the Manson-Coffin formula to calculate the fatigue life under a single cycle,calculating the fatigue cumulative damage combined with the Miner linear cumulative damage criterion to obtain the fatigue crack formation life of the space truss structure with different weld damage degree.4.Using the fuzzy model recognition methods to identify the degree of damage and the fatigue life of the space truss structure with different weld damage degree.Taking strain mode difference as the index,establishing fuzzy model library based on the key link of strain mode difference,then creating an appropriate membership function to get the membership degree of the mode to be identified with respect to the fuzzy model library,finally identifying the degree of damage and the fatigue life of the space truss structure according to the maximum membership principle.Taking a space truss structure with weld damage as example,this paper uses the fuzzy model recognition methods based on strain mode difference to identify the degree of damage and the fatigue crack formation life under random wind loads.It is suggested that this method has good recognition effect.