Quantitative Study On Crack Tip Opening Displacement Considering Thickness Effect

Crack tip opening displacement(CTOD)is one of the important parameters to evaluate whether crack propagation occurs in a cracked component.At present,most of the researches on CTOD are focused on the two-dimensional plane strain state,and there are few studies on the influence of thickness effect on CTOD,which inevitably leads to some errors between the final results and the actual size.Therefore,it is necessary to study the crack tip opening displacement quantitatively.In this paper,a CTOD quantitative model considering thickness effect is established for a finite thickness plate with a central through crack by using finite element method,which provides a basis for fatigue crack propagation and fracture assessment.The main work of this paper is summarized as follows:Firstly,the CTOD calculation model of three-dimensional hull plate with central through crack under static load is established by using finite element method,and the maximum crack opening displacement(MCOD)is introduced.Through the theoretical derivation of fracture mechanics,it can be known that there is a quantitative relationship between CTOD and MCOD when the plate thickness is considered.After finite element analysis and sorting,and combined with the least square method,the quantitative relationship between the normalized CTOD and MCOD is obtained.On the basis of this function,the crack half length(a),the applied stress are considered(),the influence of plate width effect,material properties(yield limit,Poisson’s ratio and Young’s modulus)and plate thickness on the formula is discussed.Next,the thickness reduction factor is introduced to further study the relationship between the normalized CTOD and MCOD at different positions along the thickness direction when the thickness is determined,and the quantitative formula of CTOD applicable to different thickness positions is obtained.Secondly,based on the three-dimensional cracked plate under uniaxial tensile loading,the calculation formula of crack tip opening displacement considering the thickness effect under cyclic loading is studied.When the calculation formula of crack tip opening displacement considering the thickness effect under cyclic loading is studied,the calculation formulas of crack tip opening displacement under unloading and second loading are given in this paper.At the same time,combined with the second chapter,the thickness reduction factor is introduced,and the calculation formula of the crack tip opening displacement at the position of the nonplate midplane is obtained.Then,the calculation formula of crack tip opening displacement under variable amplitude cyclic loading considering plate thickness effect is studied.In this paper,two different loading methods are considered,which are high-low and low-high loading.Through numerical calculation and data fitting,the calculation formula of crack tip opening displacement under variable amplitude cyclic loading considering plate thickness effect is obtained.Finally,this paper explores the calculation formula of crack tip opening displacement at the middle plane of plate thickness under the action of ballast load.The external stress is considered(),the effects of crack half length(a),plate width effect and material properties(yield limit,Poisson’s ratio and Young’s modulus)on the functional relationship are discussed.