Fracture Method Based On Material Damage And Its Applications In Fracture Analysis Of Tubular Joints

Tubular joints are widely used in space structures because of their simple structure and good mechanical properties.Fracture is a common failure mode of tubular joints and fracture of tubular joints can easily lead to structural collapse.Therefore,it is necessary to accurately predict the fracture behavior of tubular joints.However,the existing fracture prediction methods are difficult to predict the crack growth process and need high-precision mesh,less considering material damage,which make them difficult to reasonably predict the joint fracture process and load limit state in finite element analysis.In this paper,DCLC-based continuous damage mechanics model(D-DCLC model)was established from the micro-fracture mechanism.The accuracy of this method in predicting crack growth was proved by theory and finite element analysis.The applicability of D-DCLC model and VGM-based continuum damage mechanics model in fracture analysis of tubular joints was verified.The specific contents of this paper are as follows:(1)The basic principles and application methods of void growth model(VGM)and VGM-based continuum damage mechanics model for monotonic load,as well as cyclic void growth model(CVGM)and DCLC formula for ultra-low cycle fatigue load were summarized.(2)The crack growth process of tubular T-joints under monotonic load was predicted by using VGM-based continuous damage mechanics model.The loaddisplacement curve of T-joints were in good agreement with the experimental results,which verifies the applicability of the model in fracture analysis of tubular T-joints under monotonic loading.(3)DCLC formula was improved,and through theoretical analysis,considering reduction of mechanical properties of element due to damage caused by crack propagation,DCLC-based continuous damage mechanics model(D-DCLC model)was established.Based on DCLC formula and D-DCLC model,the VUMAT subroutine of ABAQUS finite element software was compiled to simulate crack growth by deleting failure elements.(4)Using DCLC formula and D-DCLC model,the crack growth process of unilateral notched members under ultra-low cycle fatigue load was predicted,and the fracture process was in good agreement with the predicted results of CVGM,which verified the accuracy of D-DCLC model in predicting the crack growth under ultra-low cycle fatigue load.(5)Using CVGM,DCLC formula and D-DCLC model,the crack growth process of tubular N-joints under ultra-low cycle fatigue load was predicted.The ultimate bearing capacity of the joints obtained was similar to the experimental results,which verified the applicability of D-DCLC model in fracture analysis of tubular joints under ultra-low cycle fatigue load.The D-DCLC model established and validated in this paper has great application value for fracture analysis of tubular joints under ultra-low cycle fatigue load.