In the service process of marine engineering steel structures,under the influence of extreme cyclic loads such as wind,waves,currents,or earthquakes,ultra-low-cycle fatigue fracture failures are prone to occur,causing casualties and property losses.Therefore,the analysis and prediction of ultra-low-cycle fatigue fracture are crucial for the safety assessment of marine structures.However,at present,various ultra-low-cycle fatigue life prediction models based on cumulative damage theory cannot achieve unified predictions for multiscale joints,resulting in inconvenience in practical engineering applications.Prediction of ultra-low-cycle fatigue life of X-shaped circular tube joints based on cyclic pore expansion model is conducted.Firstly,a VUSDFLD program based on the cyclic pore expansion model is developed,which realizes the joint application of ABAQUS and FORTRAN subroutines.The effectiveness of the cyclic pore expansion model in the analysis of ultra-low-cycle fatigue fracture of X-shaped circular tube joints is verified by finite element analysis.Secondly,based on multiple sets of finite element analysis results of ultra-low-cycle fatigue fracture of X-shaped circular tube joints,a prediction formula for ultra-low-cycle fatigue life based on the Manson-Coffin equation is proposed at the macroscopic level.Finally,according to the Miner theory,the prediction formula for ultra-low-cycle fatigue life applicable to constant amplitude loading is extended to variable amplitude loading conditions,and the applicability of various ultra-low-cycle fatigue formulas under different joint sizes is verified,providing a theoretical basis for engineering applications.
X-shaped circular tube jointcyclic pore expansion modelcrack initiationfracture failurefatigue life
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