PFM is widely applied in the fatigue reliability analysis of offshore structures. However some fuzzy uncertainties concerned In the prediction of offshore structure fatigue are not considered by PFM such as uncertainty in the evaluation of flaw size distribution form and parameters, fuzziness in failure criteria, subjective factor involved in design, fabrication and inspection, and so on. The paper presents a new method --- FPFM (fuzzy probabilistic fracture mechanics) to predict the fatigue reliability of offshore structure when fuzzy factors exist. Which is developed by combining fuzzy system theory and PFM. By the new method, all uncertainties (randomness and fuzziness) may be considered in fatigue reliability investigation. Some applications of FPFM are also discussed.
Probabilistic fracture mechanics (PFM) is a useful tool which IS widely applied to predict fatigue failure probability of offshore structures (Lidiard, 1979, Kirkemo, 1988). Evaluation of offshore structure fatigue and fracture is complicated by many uncertain factors (Wirsching. 1984. Martindale & et al. 1983. Karadeniz & et al. 1982). Which may be classified as two types: randomness and fuzziness. The randomness In fatigue analysis of offshore structures may be dealt with effectly be PFM (Paliou, 1986. Chen. 1986, Marshall, 1982). Using the new method life distribution of a fuzzy fatigue failure event and fatigue distribution when some parameters are fuzzy variables can be determined. In order to investigate fatigue reliability of offshore structures by PFH where both randomness and fuzziness exist, we developed a new approach --- FPFM, based on fuzzy system theory, by which the fuzzy fatigue and fracture reliability analysis can be made and the application area of PFM IS extended also. The principles of FPFM and Its applications to the fuzzy fatigue reliability analysis of offshore structure are discussed in the paper.