Study on SN-based and FCP-based Fatigue Assessment Techniques for T-Shaped Tubular Welded Joint

Abstract

Full-scale fatigue tests of the land structure's T-shaped tubular welded joints are conducted. Three-dimensional finite element (FE) fatigue crack propagation (FCP) analyses based on VCCM with tetrahedral elements are performed in order to obtain the reference SIF solutions. The preciseness of the FE FCP analyses is demonstrated by comparing calculated and measured crack propagation behaviors. Hot spot stress (HSS)-based fatigue assessments are carried out by using various fatigue design codes for tubular joints, and the safety margin of each HSS determination techniques are compared. The crack propagation lives are also predicted by carrying out FCP analyses based on Mk factor method. HSS determination techniques examined in the fatigue assessment are adopted to determine the stress concentration factor (SCF) and the degree of bending (DOB) in Mk factor calculations. It is found that the Mk factor-based FCP results show good agreement with the FE FCP results and the measurements when the HSS determination technique with the smallest safety margin is chosen. Based on these results, the method for selecting SCF and DOB calculation procedure for Mk factor-based FCP analysis is proposed. It is also shown that the difference between the fatigue test results and the HSS SN-based fatigue assessment results becomes smaller when the SIF estimated by Mk factor method agrees with the SIF calculated by the FE fracture analysis.