Bi-criteria maintenance policies for a system subject to competing wear and δ -shock failures

Abstract

We consider a deteriorating system subject to dependent competing failure modes, which fails either because its deterioration exceeds a predetermined failure threshold L (irreparable deterioration failure) or because the interval between two successive shocks is less than a threshold δ (repairable δ-shock failure). The system gradual deterioration is modelled by a Gamma process and the shocks occur following a Poisson process. The duration of a shock itself is negligible so it does not affect the system deterioration, while the δ-shock failure causes a non-negligible interruption to the production process. The threshold δ is dependent on the deterioration level. The deterioration state of the system can only be observed by inspection. The shock can be detected once it has occurred. In order to avoid the δ-shock failure caused by the shocks, a scheduled halt of the system is planned after a shock occurrence and two maintenance policies introducing the possibility of such a scheduled halt are proposed and their performances are studied. The effect and the benefit of introducing a scheduled halt of the system as a protective maintenance measure is evaluated by Pareto multi-objective optimization and Pareto front according to both cost and availability criteria.