| Always,port machinery and equipment are intermittent operating machinery and equipment,with repeated,cyclical cycle characteristics.And due to the processing technology and other reasons,there is an initial defect in the metal structure.It's easy produce more fatigue cracks under the action of alternating load.Therefore,it is of great significance to analyze the mechanism of the fatigue crack propagation based on the fracture mechanics method for the safe operation of the port equipment.In traditional fracture mechanics,the crack tip stress field is mainly dominated by the singularity of the stress intensity factor.However,further studies have found that the constant term has an effect on the crack tip stress field,especially the non-singular terms containing T-stress.In this thesis,the numerical simulation of 2D and 3D cracks is carried out,and based on the numerical results,the crack propagation characteristics are analyzed.Then the mode I fatigue crack propagation is analyzed based on the experimental method.Finally,under the condition of T-stress,the fatigue propagation life of mix-mode crack is analyzed.The main research work is as follows:(1)The stress intensity factor and T-stress of 2D and 3D cracks are numerically calculated by the interaction integral method.Then,based on the numerical results,T-stress is numerically fitted,and the relevant fitting formula is obtained.And this lays the foundation for the analysis of the influence of T-stress on crack propagation and life calculation.(2)Based on the results of numerical calculation,the influence of T-stress on crack propagation is analyzed.The effects of T-stress on fracture toughness and propagation angle are analyzed respectively for mode I crack and I-? mix-mode crack.(3)The finite element method is used to simulate the crack propagation,and the 2D edge crack and mix-mode crack propagation are simulated respectively.Then,based on the Ramberg-Osgood elastoplastic model and the biaxial load model,the effect of T-stress on crack propagation was analyzed.(4)Taking the three-point bending beam specimen of high-strength structural steel as the experimental object,the propagation of mode I crack under fatigue load is analyzed,and obtain the propagation life curve and the parameters of the relevant Paris formula.Based on the numerical simulation results,the life of the specimen is calculated,and verified the validity of the numerical simulation method by comparing the numerical simulation results and experimental results.(5)Under the condition of T-stress,the mathematical model of life prediction of I-? mix-mode crack propagation is established,and verified the validity of mathematical model based on the numerical results.Then,the mathematical model of fatigue life calculation based on energy release rate was established,and the simulation results are compared with the traditional Paris formula,which verifies its effectiveness and provides the theoretical basis for fatigue crack propagation life calculation. |
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