Strength-based reliability and fracture assessment of fuzzy mechanical and structural systems

In most mechanical and structural systems, a certain amount of uncertainty exists in both strength and load values. The uncertainty of these values must be taken into consideration when quantifying the safety and reliability of a system. Fuzzy set theory has been used for the description and analysis of such systems. A means for comparing fuzzy strength and load values is needed to determine the safety and reliability of fuzzy mechanical and structural systems. The concepts of fuzzy bounds and subsethood are used here to define a safety index for mechanical or structural systems based on fuzzy load and strength values. Similarly, a criticality index for fracture damage assessment is defined based on fuzzy stress intensity factors. The concept of a fuzzy factor of safety is also introduced. The proposed safety and criticality indices and the fuzzy factor of safety could provide useful measures for rating designs in terms of strength-based reliability and damage tolerance. The application of the proposed measures in the assessment of damage as reported by online structural damage detection systems is also suggested.

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