Estimation Of Stress Intensity Factor Solutions For Cracks In Tubular Joints Based On Crack Opening Displacement

Tubular joints are widely applied in the offshore platforms as part of supporting structures. Because of cyclic loads caused by seawater wave and wind, Tubular joints which are the weakest structures to become fatigue failure can easily come into being the surface cracks in the weld toe. Fracture Mechanics based on stress intensity factor is a rational method to estimate residual life of such damaged structures. Thus, the accurate calculation of stress intensity factor for cracks in offshore tubular joint is foundation of estimation residual life of offshore structures. So it is significant to estimate stress intensity factor solutions for weld toe surface cracks in offshore tubular joints accurately and rapidly in engineering.Crack opening displacement can be meansured by some methods. In this paper, it sets up a relationship between stress intensity factor and crack opening displacement, surface crack shape, tubular joint shape. So it can calculate stress intensity factor for tubular joint rapidly if structure parameters can be measured. The main work in the thesis is outlined as follows;Firstly, it is a review of background of this essay and detection technology, the content of the study is presented. In the Chapter two, the concept of stress intensity factor and the method of calculation are introduced.Chapter three and Chapter four are main part of the thesis. In Chapter three it discusses how to make a finite element model for weld toe cracks in offshore typical tubular K-joint. Based on the foundation supposition, it discusses the precision to calculate stress intensity factor along with the length of the first element in crack tip and the grid density of the whole model. In the Chapter four, it calculates stress intensity factor with different geometric parameters, and it provide a relationship with the method of BP neural network between stress intensity factor and crack opening displacement, surface crack shape, tubular joint shape. So it can estimate stress intensity factor for weld toe cracks rapidly if it can detect the the surface crack opening displacement.It's turn out that the gap between the method metioned in this essay and numerical anslysis can be less than 1%. Because of its high efficiency, simpleness, the method can be applied to engineering.