Probability distribution models for geometric and crack shape factors of SIFs in tubular K-joints under balanced axial loads

The stress intensity factor (SIF) is one of the crucial parameters in evaluating the fatigue reliability of offshore tubular joints based on the fracture mechanics (FM) approach. The value of SIF is a function of the crack size, nominal stress, and two modifying coefficients known as the crack shape factor (Yc) and geometric factor (Yg). These coefficients exhibit considerable scatter which calls for greater emphasis in accurate determination of their governing probability distributions. As far as the authors are aware, no comprehensive research has been carried out on the probability distribution of geometric and crack shape factors in tubular joints. What has been used so far as the probability distribution of these factors in the FMbased reliability analysis of offshore structures is mainly based on assumptions and limited observations, especially in terms of distribution parameters. In the present paper, results of parametric equations available for the computation of Yc and Yg have been used to propose probability distribution models for these factors in tubular K-joints under balanced axial loads. Based on a parametric study, two samples were prepared for Yc and Yg; and the density histograms were generated for these samples using Freedman-Diaconis method. Ten different probability density functions (PDFs) were fitted to these histograms. The maximum likelihood (ML) method was used to determine the parameters of fitted distributions. In each case, Kolmogorov-Smirnov test was used to evaluate the goodness of fit. It was concluded that Birnbaum-Saunders and Gamma distributions are the best probability models for the geometric and crack shape factors in tubular K-joints under balanced axial loads, respectively.

کلیدواژه ها:

Tubular K-joint ، Stress intensity factor (SIF) ، Geometric factor ، Crack shape factor ، Probability density function (PDF)