Abstract:

To address the problem of life assessment for thin-walled cracked steel circular tube under tension-torsion composite fatigue loading， this paper conducts a study on the fatigue crack propagation mechanism. Firstly， based on the maximum circumferential stress criterion and the Paris equation， a analysis model for crack propagation of pre-cracked thin-walled steel circular tube subjected to tension-torsion biaxial proportional in-phase cyclic loading is established. Secondly， based on existing fatigue tests， the interactive techniques of finite element software ANSYS and FRANC3D is jointly used to simulate the crack propagation behavior of steel circular tube， validate this paper's proposed composite crack propagation analysis model. Finally， based on the finite element model， parameter analyses are conducted on factors such as shear-to-tensile stress ratio， diameter-to-thickness ratio， and initial damage size. The results demonstrate that this paper's proposed analysis model accurately predicts crack propagation behavior of thin-walled steel circular tube （with diameter-to-thickness ratios exceeding 10） under tension-torsion composite fatigue loading. Under tension-torsion in-phase proportional fatigue loading conditions， the composite cracks in thin-walled steel tubes quickly evolve into opening-mode （Mode I） cracks， with the crack propagation angle determined by the maximum nominal shear-to-tensile stress ratio. The shear-to-tension stress ratio and initial damage length were identified as the primary factors on the composite crack propagation behavior of the steel circular tubes under small-scale yield condition with the identical maximum principal tensile stress and stress ratio.

Key words: tension-torsion composite fatigue, thin-walled steel circular tube, crack propagation, in-phase proportional cyclic loading, shear-to-tension stress ratio