Experimental And Theoretical Study On Static And Constant Amplitude Fatigue Behavior Of Welded Cross Plate-hollow Sphere Suspension Joints In Space Frame Structures

Aiming at the space frame structure with suspension crane,the fatigue problem of suspension joints is the key to the fatigue of the space frame structure.The welded cross plate-hollow sphere joint("plate-sphere" joint for short)is one of the most commonly used suspension joints,however,the fatigue design theory and method in the current code and manual is not clear,which caused that suspension crane can not be widely used in space frame structure,therefore,it is particularly important to research the fatigue problem of this kind of joints! This paper was supported by National Natural Science Foundation Project(51578357)and Natural Science Foundation Project of Shanxi(2015011062),aiming at commonly used suspension joints—"plate-sphere"joints,experimental and theoretical study on static and constant amplitutde fatigue behavior was conducted,the main research work and conclusions are as follows:1.Based on field investigation around Taiyuan,combining with design code and manual related to suspension joints,adopting orthogonal experimental design method,using cross plate width B,cross plate thickness t,welded hollow sphere diameter D and wall thickness ? as variables,which were considered at three values,9 joint specimens were designed and finished.2.Based on MTS testing machine,static tests of 8 specimens of joints were conducted,static finite element analysis of 9 joints were analysed by ANSYS and ABAQUS,stress distribution and location of hot spot stress in the joint were presented;aiming at "plate-sphere" joints,main factors related to stress concentration were discussed,influence degree and correlation of different factors were presented;formula of hot spot stress concentration factors considered reduced factor by leg size of fillet weld was established,and taking value interval is from 3.59 to 5.41.3.Fatigue behavior testing with constant amplitude in higher stress range of 8 "plate-sphere" joints were completed by MTS testing machine,through which 7 effective constant fatigue testing data were obtained;combined with the existing 19 constant amplitude fatigue test data,rejected 3 abnormal point,S-N curve with 95%confidence interval was acquired by linear regression analysis,and nominal allowable stress amplitude of joint was calculated,namely[??]2×106 =19.05MPa.4.Constant amplitude fatigue life of "plate-sphere" joints were estimated through fracture mechanics method,which was lower than fatigue life by test;emphasis on discussing the influence of different initial crack length on the crack propagation life,concluded that if the initial crack size increases ten times,the fatigue life of the crack propagation is reduced by about 70%.5.Finite element analysis about "plate-sphere" joints with or without weld was conducted by XFEM technology of ABAQUS,concluded that crack initiation and propagation direction were affected by weld;compared with test results,the suggested values about the key control parameters of this kind of joint with the constant amplitude fatigue test were presented:recommended displacement value of joint with crack initiation is 5%?U;displacement value of specimen failure is 10%?U.