Fatigue Crack Propagation Research Of Ship Stiffened Plate Under The Combined Load

Fatigue strength is a key factor for the evaluation of hull structure performance.Fracture mechanics method is paid more and more attention to analyze the fatigue strength of hull structure.At present,single load is considered in most assessment based on fracture mechanics.However,the stiffeners of the hull are subjected to not only longitudinal load,but also local load such as cargo and equipment pressure.So,the combined axial-lateral load should be considered in this case.In order to effectively analyze the fatigue strength of stiffened plates under combined axial-lateral load,the crack propagation of stiffened plate under combined axial-lateral load is studied.The main works are as follows:1.The methods of crack propagation analysis are briefly introduced.The characteristics of several crack growth rate models and fracture criterion are analyzed.Different methods for stress intensity factor calculation are compared.Then,the Paris model is selected for numerical and experimental analysis of the crack propagation under combined axial-lateral load.2.The finite element method is applied to calculate the stress intensity factor.The method for stress intensity factor calculation of the stiffened plate crack tip under combined axial-lateral load is researched.The boundary conditions and load forms are reasonably defined.The effect of residual stress on stress intensity factor is analyzed.3.The fatigue crack propagation tests of stiffened plates under combined axial-lateral load are conducted.Through the tests of fatigue crack propagation under several combined axial-lateral loads with different phases,the corresponding a-N curve is obtained.Numerical simulation result is compared with test result to verify the accuracy of numerical simulation method.4.The numerical method is applied to check the fatigue strength of ship stiffeners.The stress intensity factors of the stiffener crack tip with different lengths are calculated.The process of fatigue crack propagation of stiffener is analyzed.Then,the fatigue life of target stiffener can be assessed.