Stress intensity factors for ship and offshore structural details

Abstract

Fatigue is responsible for a great proportion of crack occurring in ships and offshore structures. Fatigue strength assessment is mandated to evaluate and develop procedures for estimating the fatigue strength and providing recommendations. The traditional approach to the fatigue analysis of notched structural components has been based on the classical S-N curve. The empiricism of this approach has led to the exploration of recently developed disciplines, fracture mechanics and low cycle fatigue, to develop methods for more rational and accurate analyses. The objective of the current study is, therefore, not only to extend the understanding to the fatigue evaluation by linear elastic fracture mechanics approach, but also to apply this method on the evaluation the weld root cracking for doubler-plate reinforced joints. Evaluation of stress intensity factor by finite element method has been calibrated against reported numerical and experimental results. For the purpose of standardized and simplified crack mesh generation, an automatic crack mesh generator program has been developed. Studies have been carried out on the weld root cracking of load-carrying cruciform joint, and comparison between the obtained results and reported results has been carried out for calibration purpose. Studies have been carried out on the weld root cracking of doubler-plate reinforced joints. Comparison between weld root cracking and weld toe cracking as well as between 2-D analyses and 3-D analyses have been carried out to identify the governing condition. Parametric studies have been carried out on the weld root SIF of doubler-plate reinforced joints. More than 900 analyses have been carried out on the doubler-plate reinforced plate connections on near 200 different geometric configurations. Another 120 analyses have been carried out on doubler-plate reinforced circular hollow section (CHS) X-joints on 60 different geometric configurations. The parametric study has identified the critical position in terms of root cracking, as well as determined the influences of the major geometric parameters.