Quantitative Research On The Crack Tip Opening Displacement During Crack Propagation

Crack tip opening displacement(CTOD)is one of the main parameters to evaluate crack propagation of ductile material,the construction of modern ships and marine structures requires a great deal of steel,fracture is one of the common forms of steel structure failure.The dynamic process of crack propagation increases the complexity of the stress and strain field at crack tip region.so far,the research on crack tip opening displacement is carried out mainly in the case of static crack,and the finite element method is one of the main methods to study such problems.This paper is based on elastic-plastic fracture mechanics.In this paper,the changing rule of crack tip opening displacement amplitude(?CTOD)is studied under cyclic loading with theory of elastic-plastic fracture mechanics and finite element numerical simulation technology,finally,a simple model for calculating ?CTOD is presented,it provides reference value for fracture evaluation and crack propagation of materialsThe main work of this paper is summarized as follows.Firstly,the maximum crack opening displacement(MCOD)parameter is introduced.In the case of constant cyclic tensile loading,it is proved that there is an internal connection between the maximum crack opening displacement amplitude(?MCOD)and ?CTOD with theoretical analysis,then,the ?CTOD calculation model based on ?MCOD is established with finite element numerical simulation.And then the influence of large scale yield,plate width,initial crack length,stress ratio,material properties(yield strength,elastic modulus and material hardening)on the established model is further analyzed,and correspondingly,the formula is modified according to the influence of these parameters for a wider range of applications.Subsequently,based on the results in constant amplitude cyclic tensile loading scenario,the effect of tensile overload is investigated.The results show that the tensile overload significantly increases ?CTOD,after that,the displacement of crack tip is gradually reduced with the crack propagation,and finally,it gradually returns to the stable value before the overload.The decrease of ?CTOD after overload explains the overload hysteresis effect of crack propagation,and the stable value of ?CTOD can be evaluated by the previous formula.Finally,based on the results in constant amplitude cyclic loading scenario,the effect of compressive load section on ?CTOD is studied,and a calculation formula for ?CTOD under cyclic tensile-compressive load is established based on ?MCOD,then the influence of external load,material properties(yield strength,elastic modulus and material hardening)and the ratio of plate width to initial crack length were further investigated,and correspondingly,the formula is modified according to the influence of the above parameters for a broader range of applications.