Research On The Interface Strength Of Steel-aluminum Joint Based On Cohesive Zone Model

At present,more and more ships adopt aluminum alloy superstructure.In the traditional ship structure,aluminum alloy and steel is connected by riveting or bolt connection.And the use of steel-aluminum joint,has the advantages of improving the construction conditions,reducing labor intensity and improving the water tightness and corrosion resistance of the connected part.As one of the most important structures of ships,steel-aluminum joints have attracted widespread attention from ship design and users.The cohesive zone model based on the theory of damage mechanics has a strong advantage in dealing with the interface problem of composite materials.Therefore,based on the cohesive zone model,this paper studies the interface strength of the steel-aluminum joint.However,there is no mature cyclic cohesive zone model theory and numerical simulation technology,and the cohesive zone model is rarely used to study the interface of steel-aluminum joints.In order to further improve the engineering applicability of cohesive zone model,and provide guidance for the preparation of steel-aluminum joint,and provide assessment methods for the safety status of steel-aluminum joint during the process of using,this paper studies on the theory of cohesive zone model,the development of UMAT subroutine of the monotonous cohesive zone model and the cyclic cohesive zone model,and the accuracy of the subroutine is verified.On the basis of the subroutine,the interface strength of steel-aluminum joint is studied.Firstly,the monotonous cohesive zone model is introduced,and the constitutive relationship of the bilinear cohesive zone model under mixed-mode fracture is explained.The principle of constructing the cyclic cohesive zone model based on the monotonous cohesive zone model is explained.And the core contents of the UMAT subroutine for cohesive zone model based on ABAQUS is explained.Secondly,the accuracy of the UMAT subroutine of the monotonous cohesive zone model was verified by single-cell model from three aspects of pure normal,pure tangential and mixedmode.The monotone cohesive zone model was used to simulate the type I crack of the double cantilever beam,the type II crack of the end-notch flexure specimen and the type I and II composite crack of the mixed-mode bending specimen.Then,the effects of load amplitude,load frequency,load ratio,number of load cycles and the parameters of the fatigue damage model on the cyclic cohesive zone model were studied respectively.Next,the trabecular bending specimen for fatigue test,the split specimen for fatigue test,Four-point end-notch flexure specimen and the mixed-mode crack specimen were simulated to verify the accuracy of the cyclic cohesive zone model in predicting the crack growth life.Finally,the pre-and post-processing techniques of the numerical simulation for the interface of steel-aluminum joint were studied,including the establishment of the wave interface,the automatic generation of the zero-thickness cohesive elements and the acquisition of the interface crack growth length.The effects of the wave interface with different shapes and the modulus of the materials above and below the interface on the static interface strength and fatigue interface strength of the steel-aluminum joint were studied.