| Ship and marine engineering because of its complex structure, at the same time, in the harsh working environment,can lead to fatigue crack initiation in the local area to ship and ocean engineering structures, the fatigue crack growth rate reaches a certain value, the ship and ocean engineering structures will be some damage occur through the fatigue crack propagation therefore, through the research on fatigue crack propagation of ship and ocean engineering, in order to ensure the safety of ship and ocean engineering structures. So it is of certain significance to fatigue crack steel expansion of ship and ocean engineering structures.This paper is divided into four parts to study:(1)A detailed analysis of the metal Q235 structure crack in fatigue crack damage at different stages of initiation, and described the different characteristics of each stage of crack initiation, crack fatigue damage mechanism is analyzed from the fundamental. Detailed discusses the commonly used in solving the problem of structural fatigue method, including the model test method, the numerical simulation method, the fracture mechanics method,evaluation method of S-N fatigue curve, as the crack opening displacement theory for fatigue strength analysis done to pave the way based on the. At the same time, a detailed analysis of the study on the growth rate model for different crack tip, and the different models in the performance results are compared and analyzed, the calculation of crack propagation rate is a better model selection.(2)The fatigue crack growth rate tests on steel for shipbuilding steel, to determine the crack growth rate and the crack tip opening displacement. Determination of the crack length by compliance method, and 50 times optical reading microscope detection results were compared and analyzed, validated the feasibility by optical methods to measure the length of crack extension. Analysis and calculation of the fatigue crack growth rate da/dN, the application of the method to the traditional seven point incremental polynomial method, and the data were analyzed. In the test of fatigue crack propagation rate of crack mouth opening displacement,through the conversion CTOD, and the calculation of linear Q235 steel fatigue crack growth rate of the regression formula, to follow through the crack tip opening displacement method provides a basis for the calculation of ship fatigue strength.(3)The foundation through the fatigue crack propagation rate of the test, on the fatigue crack propagation in the material parameters of C and m were statistical analysis it is found that there are some dispersion, and the dispersion that conforms to the laws of a certain statistical distribution. The fatigue crack propagation by Paris formula fitting, the fitting parameters of C and m has certain statistical correlations. The parameter C can be based on the parameters of m normal distribution on the correlation to determine the. Parameters of C obeys the lognormal distribution based on m in order to determine the parameters of. The follow-up analysis of structure fatigue hull provides average Paris formula better reliability.(4)To simulate the regional structure of hull structure crack by finite element modeling,according to the calculation method of fatigue crack propagation criterion of CTOD crack opening displacement is studied based on the fatigue life of crack, and the S-N curve method based on the results of comparative analysis. |
