A two-stage reliability optimization approach for solving series-parallel redundancy allocation problem considering the sale of worn-out parts

Redundancy allocation is one of the methods of enhancing the reliability of a system. The components are specified and located based on a non-linear problem. In all problems, a few subsystems are selected to add the parts. Then, the allocation takes place and the new value of reliability is measured. Designers considered a constraint for reliability, and problem-solving at zero time is not the best strategy. Since the reliability decreases over time, this study focused on an approach for two stage reliability optimization to solve series-parallel redundancy allocation problem considering sale of worn-out parts. One a portion of the budget will be spent on maximizing reliability as the system is launched. Other; the reliability reaches its minimum acceptable value, while the remaining budget will be spent on replacement of system's parts. When a component of the system is replaced earlier than its lifetime, the available budget can be expanded based on the book value of the component. In fact, this model allows the sales of components used in this model. Moreover, the replacement time is calculated based on the constraint set for the level of reliability. It has also highlighted that the cost is significantly reduced with the proposed approach. In this model, both the solution and results are used at zero time. Finally, the mathematical model is examined by an example.