Research On Fatigue Property Of Typical Circular-to-Circular And Circular-to-Rectangular Welded Tubular Joints

Hollow section structure is widely used in all aspects of society, in the process of using structures are subjected to a variety of fatigue loading, the fatigue loading will induce the joints' fatigue damage which sometimes may cause serious accidents. So the previous design method which only considered merely the carrying capacity of structure will become unsafe, we must also check the fatigue life of the hollow section structure. Welded tubular Joint is the common connection in the hollow section structure, which has many types, including circular hollow section joint, rectangular hollow section joint, hybrid hollow section joint. For the previous research, the fatigue characteristics of circular and rectangular hollow section joint are widely analyzed, but the research of hybrid hollow section joint is lacked. In this paper, a variety of welded structure fatigue analysis method were used to analyze the fatigue property of typical circular-to-circular and circular-to-rectangular welded tubular joints for engineering use. The main contents are as follows:(1) At first, we comprehensively describe the common research methods of welded structure fatigue analysis, the hot spot stress approach, effective notch stress approach, the local stress and strain approach.(2) The reliability of using finite element method to analyze the stress concentration factor of hollow section joint was verified. A series of analysis about the stress concentration factor of welded circular tubular N-joint under balanced axial load was produced, the effect of some main geometrical parameters on the stress concentration factor of N-joints under balanced axial load is investigated and the parametric equations to calculate the stress concentration factor of N-joint under balanced axial load have been proposed.(3) The effect of some main geometrical parameters on the stress concentration factor of circular-to-rectangular(CHS-to-RHS) Y-joint under axial load is investigated and the parametric equations to calculate the stress concentration factor of circular-to-rectangular Y-joint under axial loads have been proposed.(4) The effect of some main geometrical parameters on the stress concentration factor of circular-to-rectangular(CHS-to-RHS) K-joint under balanced axial loads is investigated and the parametric equations to calculate the stress concentration factor of circular-to-rectangular K-joint under balanced axial loads have been proposed.(5) The effective notch stress approach was used to investigate the fatigue property of circular-to-rectangular(CHS-to-RHS) T-joint under axial load, which proved to be practicable, we get the parameter formula of circular-to-rectangular T-joint under axial load to calculate the notch stress concentration factor. At the same time, the fatigue life of the hot spot stress approach shows good agreement with the effective notch stress approach.(6) At last, the local strain approach was used to investigate the fatigue life of circular-to-rectangular(CHS-to-RHS) T-joint under axial load, and the modified Neuber method was adopted to calculate the local elastic-plastic stress and strain of the T-joint, the results got by local strain approach are consistent with experiments.