Reliability Based Optimization for Quality Assurance

The present paper proposes a concept of Reliability Based Optimization (RBO) for quality assurance. In general the RBO approach is viewed as a minimization of the expected total cost of the structure including initial costs and costs due to failure, weight minimization with respect to reliability constraints, etc. The aim of the reliability based optimization is to find the best compromise between cost reduction, safety and reliability. Nevertheless, it is well-known that structures will normally degrade their structural performance during lifetime in a way that depends on their nature. Typical degrading phenomena under normal operational conditions are corrosion and fatigue effects. This leads to the development of an inspection and repair program which is known as maintenance. One of the most widely used methods for inspection is Nondestructive Inspection (NDI). Hence, in order to maintain the structural components in a good condition, NDI is required at regular intervals and the results can be used for maintenance to mitigate fatigue risk. In order to take into account the effect of NDI into an RBO concept, the parameters of inspection and repair activities are to be optimized, i.e. aimed at the minimization of the overall lifetime costs. In this paper the effect of inspection quality on the probability of failure at each inspection interval is considered. By using the proposed framework, the optimization procedure for fatigue analysis in order to derive an appropriate quality assurance program can be obtained. A numerical example of inspection planning using the proposed method is presented and discussed.