An interval failure assessment diagram method for analyzing the reliability of structure containing crack defect

The failure assessment diagram (FAD) is the most widely used method for analyzing the reliability of structure containing crack defect. In practical engineering, the failure assessment point (FAP) and failure assessment curve (FAC) are impossible to be determined accurately. Therefore, an interval failure assessment diagram (IFAD) method is proposed in this paper to analyze the reliability of structure containing crack defect when the FAP and FAC cannot be obtained accurately. Firstly, based on the interval method and FAD method, an interval failure assessment diagram (IFAD) model is established by considering the FAP and the failure critical point (FCP) as interval variables. And then the FAP and FCP intervals are converted into the normalized region to design the IFAD reliability index [Formula: see text] according to the relationship between the limit state function and the normalized region. The structural arbitrary state can be described by the IFAD reliability index [Formula: see text]. In addition, 10 cases are given as examples to clearly expound the IFAD method, and the analysis results are compared with the FAD method, which confirms that the IFAD method is feasible and valid to analyze the structural reliability with the bounds of FAP and FCP. Finally, the IFAD reliability analysis of a certain propellant storage tank ellipsoidal bottom containing surface crack is taken as an application example to verify the practicability of the proposed method. And the results show that the IFAD reliability index can be obtained without the exact value of parameters.