Maintenance and Spares Optimization

Joint optimization of inspection, maintenance, and inventory for repairable systems

We developed mathematical models to find simultaneously the optimal periodic inspection interval as well as maintenance actions for systems with hidden failures. Two types of system were considered: a k-out-of-n system and a multi-component system with soft and hard failures. The developed optimization models find the optimal inspection interval and decide whether a failed component should be minimally repaired or replaced. The paper "Joint maintenance and inspection optimization of a k-out-of-n system", written based on this work received the best paper award of the 2016 American Society for Quality (ASQ)-Reliability Division (RD). We have also extended these models to the case of non-periodic inspection. Moreover, we developed optimization models to simultaneously find the optimal inspection interval and the inventory level for a k-out-of-n system. The paper "Optimizing simultaneously inspection interval and inventory levels (s, S) for a k-out-of-n system", written based on this work received the third best student paper award of the 2014 Annual Reliability and Maintainability Symposium (RAMS).

Inspection optimization of repairable systems

We developed several optimization models for inspection of multi-component systems subject to hard and soft failures. Hard failures are either self-announcing or the system stops when they take place; so, they are fixed instantaneously. Soft failures are unrevealed and can only be detected at inspections, but they do not stop system functioning. First, we developed an inspection optimization model for a multi-component system subject to periodic and opportunistic inspections. The paper "Optimum Inspection Interval for a System under Periodic and Opportunistic Inspections", written based on this work, until recently, was listed by IIE Transactions as one of the most read articles of all time, and is highlighted in Industrial Engineer Magazine. Then, we developed a model assuming that the components with hard failure are preventively replaced at periodic inspections. In addition, we developed a mathematical model to find the optimal inspection interval for a k-out-of-n load-sharing system, in which the failure of a component increases the work load on the remaining components. We also developed inspection optimization models for non-periodic inspection of k-out-of-n and multi-component systems.