Performance and cost analysis of repairable systems under imperfect repair

Operating systems do not consistently perform their intended function or mission due to improper maintenance and degradation, and thus eventually fail. Upon failure, they are either repaired or replaced; critical and non‐expensive systems are usually replaced, whereas expensive and non‐critical systems are repaired. Repair can be perfect, where the failed system becomes as good as new, or imperfect. In imperfect repair, a failed system is repaired several times before complete replacement. In this paper, the behaviour of complex repairable systems undergoing imperfect repair is examined. In this regard, an optimisation model is developed with the objective of minimising system's cost at a desired level of availability. Analytical expressions for availability and the optimal cost are derived for simple and non‐complex systems; however, simulation is used for assessing complex systems. The analysis revealed that optimal solutions are highly dependent on the structure of the configuration and the desired level of performance.