Finite Element Numerical Simulation And Experimental Study On Tension-Compression Fatigue Damage Of Steel Structure Member

Fatigue damage often appeared in steel structures at low stress and low deformation, thus the damage showed more concealment and led to huger losses. According to statistical of engineering failure cases, about 50%-90% cases of fracture failure were caused by fatigue damage, which showed the importance of analysis on fatigue damage.In this paper, based on elastic plastic fracture mechanics and finite element theory and combined with previous studies, corrections of Lemaitre damage constitutive relation was proposed and applied in fatigue damage analysis and then high and low cycle fatigue damage constitutive equation was put forward; user subroutine based on fatigue damage constitutive equation was constructed under ANSYS USERMAT subroutine to implement programmed design on fatigue damage.Based on theoretical analysis, tension-compression fatigue test was carried out with round shoulder specimens and round slot specimens to simulate the type of stress distribution in which fatigue damage of steel structure member was easy to occur. Combined with fatigue damage constitutive equation subroutine proposed in this paper, stress response and fatigue life of specimens were calculated and compared with test results, and then correctness and applicability of finite element method were verified.According to analysis results, the calculation results of finite element method proposed in this paper was approximately the lower limit of test results, meanwhile, the failure mode of fatigue damage was highly centralized:in the whole cycle life of specimens, damage appeared just locally, and initiated differently by the position of specimens. With the decreasing of concentration degree of stress distribution in material, the cycle life with carrying capacity decreasing significantly cause by damage would increase correspondingly, therefore the decrease of stress concentration degree increased the fatigue limit of material.Finite element method proposed in this paper used increment-type constitutive equation and was suitable for both proportional and non-proportional loading, meanwhile the subroutine included USERMAT subroutine based on fatigue damage and ANSYS macro file based on APDL language, thus this method was suitable for programmed design in engineering problems, providing certain reference for engineering design.