Numerical Analysis Of Fatigue Crack Forbird Beak X- And K- Joints

The bird-beak square hollow section(SHS)welded joints have the advantages of aesthetically appealing,releasing the lateral load,high rigidity,and great bearing capacity so that they can be used in bridge structures,building structures,and ocean structures,etc.However,the fatigue behaviors and corresponding fatigue design methods of bird-beak SHS joints are far from complete.This thesis focuses on the fatigue crack propagation of both square and diamond bird beak joints under repeated loads.The contents are as follows:(1)Finite element model for both square and diamond bird beak X-and Kjoints was established by using the solid elements.Static analysis considering brace axial forces and brace in-plane bending forces was performed with the aims of obtaining hot-spot stresses at weld toes.The stress concentration factors(SCFs)were calculated by means of quadratic extrapolation method,and the critical locations prone to fatigue crack initiation have been identified for such types of innovative tubular joints.(2)The fatigue crack growths of considered bird beak joints were simulated by using the software of FRANC3 D in conjunction with ABAQUS,in which the linear elastic fracture mechanics(LEFM)was involved.By inserting an initial crack in the most critical hot-spot location,the entire process of crack propagation from the initiation until the failure was numerically revealed.The simulation results were also validated by the available experimental data,which suggests the constructed models are accurate and efficient.(3)By using the validated models,a parametric study was further carried out by considering different hot-spot stress ranges and various initial crack lengths.The influences of these important parameters on the fatigue crack propagation life and propagation length were revealed,based on which some useful recommendations regarding fatigue design of bird-beak joints have been presented.